{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

-}


{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE LambdaCase #-}

{-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

-- | Typechecking instance declarations
module GHC.Tc.TyCl.Instance
   ( tcInstDecls1
   , tcInstDeclsDeriv
   , tcInstDecls2
   )
where

import GHC.Prelude

import GHC.Hs
import GHC.Rename.Bind ( rejectBootDecls )
import GHC.Tc.Errors.Types
import GHC.Tc.Gen.Bind
import GHC.Tc.TyCl
import GHC.Tc.TyCl.Utils ( addTyConsToGblEnv )
import GHC.Tc.TyCl.Class ( tcClassDecl2, tcATDefault,
                           HsSigFun, mkHsSigFun, findMethodBind,
                           instantiateMethod )
import GHC.Tc.Solver( pushLevelAndSolveEqualitiesX, reportUnsolvedEqualities )
import GHC.Tc.Gen.Sig
import GHC.Tc.Utils.Monad
import GHC.Tc.Validity
import GHC.Tc.Zonk.Type
import GHC.Tc.Zonk.TcType
import GHC.Tc.Utils.TcMType
import GHC.Tc.Utils.TcType
import GHC.Tc.Types.Constraint
import GHC.Tc.Types.Origin
import GHC.Tc.TyCl.Build
import GHC.Tc.Utils.Instantiate
import GHC.Tc.Instance.Class( AssocInstInfo(..), isNotAssociated )
import GHC.Core.Multiplicity
import GHC.Core.InstEnv
import GHC.Tc.Instance.Family
import GHC.Core.FamInstEnv
import GHC.Tc.Deriv
import GHC.Tc.Utils.Env
import GHC.Tc.Gen.HsType
import GHC.Tc.Utils.Unify
import GHC.Builtin.Names ( unsatisfiableIdName )
import GHC.Core        ( Expr(..), mkApps, mkVarApps, mkLams )
import GHC.Core.Make   ( nO_METHOD_BINDING_ERROR_ID )
import GHC.Core.Unfold.Make ( mkInlineUnfoldingWithArity, mkDFunUnfolding )
import GHC.Core.Type
import GHC.Core.SimpleOpt
import GHC.Core.Predicate( classMethodInstTy )
import GHC.Tc.Types.Evidence
import GHC.Core.TyCon
import GHC.Core.Coercion.Axiom
import GHC.Core.DataCon
import GHC.Core.ConLike
import GHC.Core.Class
import GHC.Types.Var as Var
import GHC.Types.Var.Env
import GHC.Types.Var.Set
import GHC.Data.Bag
import GHC.Types.Basic
import GHC.Types.Fixity
import GHC.Driver.DynFlags
import GHC.Driver.Ppr
import GHC.Utils.Logger
import GHC.Data.FastString
import GHC.Types.Id
import GHC.Types.SourceFile
import GHC.Types.SourceText
import GHC.Data.List.SetOps
import GHC.Types.Name
import GHC.Types.Name.Set
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Types.SrcLoc
import GHC.Utils.Misc
import GHC.Data.BooleanFormula ( isUnsatisfied )
import qualified GHC.LanguageExtensions as LangExt

import Control.Monad
import Data.Tuple
import GHC.Data.Maybe
import Data.List( mapAccumL )


{-
Typechecking instance declarations is done in two passes. The first
pass, made by @tcInstDecls1@, collects information to be used in the
second pass.

This pre-processed info includes the as-yet-unprocessed bindings
inside the instance declaration.  These are type-checked in the second
pass, when the class-instance envs and GVE contain all the info from
all the instance and value decls.  Indeed that's the reason we need
two passes over the instance decls.


Note [How instance declarations are translated]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is how we translate instance declarations into Core

Running example:
        class C a where
           op1, op2 :: Ix b => a -> b -> b
           op2 = <dm-rhs>

        instance C a => C [a]
           {-# INLINE [2] op1 #-}
           op1 = <rhs>
===>
        -- Method selectors
        op1,op2 :: forall a. C a => forall b. Ix b => a -> b -> b
        op1 = ...
        op2 = ...

        -- Default methods get the 'self' dictionary as argument
        -- so they can call other methods at the same type
        -- Default methods get the same type as their method selector
        $dmop2 :: forall a. C a => forall b. Ix b => a -> b -> b
        $dmop2 = /\a. \(d:C a). /\b. \(d2: Ix b). <dm-rhs>
               -- NB: type variables 'a' and 'b' are *both* in scope in <dm-rhs>
               -- Note [Tricky type variable scoping]

        -- A top-level definition for each instance method
        -- Here op1_i, op2_i are the "instance method Ids"
        -- The INLINE pragma comes from the user pragma
        {-# INLINE [2] op1_i #-}  -- From the instance decl bindings
        op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
        op1_i = /\a. \(d:C a).
               let this :: C [a]
                   this = df_i a d
                     -- Note [Subtle interaction of recursion and overlap]

                   local_op1 :: forall b. Ix b => [a] -> b -> b
                   local_op1 = <rhs>
                     -- Source code; run the type checker on this
                     -- NB: Type variable 'a' (but not 'b') is in scope in <rhs>
                     -- Note [Tricky type variable scoping]

               in local_op1 a d

        op2_i = /\a \d:C a. $dmop2 [a] (df_i a d)

        -- The dictionary function itself
        {-# NOINLINE CONLIKE df_i #-}   -- Never inline dictionary functions
        df_i :: forall a. C a -> C [a]
        df_i = /\a. \d:C a. MkC (op1_i a d) (op2_i a d)
                -- But see Note [Default methods in instances]
                -- We can't apply the type checker to the default-method call

        -- Use a RULE to short-circuit applications of the class ops
        {-# RULE "op1@C[a]" forall a, d:C a.
                            op1 [a] (df_i d) = op1_i a d #-}

Note [Instances and loop breakers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Note that df_i may be mutually recursive with both op1_i and op2_i.
  It's crucial that df_i is not chosen as the loop breaker, even
  though op1_i has a (user-specified) INLINE pragma.

* Instead the idea is to inline df_i into op1_i, which may then select
  methods from the MkC record, and thereby break the recursion with
  df_i, leaving a *self*-recursive op1_i.  (If op1_i doesn't call op at
  the same type, it won't mention df_i, so there won't be recursion in
  the first place.)

* If op1_i is marked INLINE by the user there's a danger that we won't
  inline df_i in it, and that in turn means that (since it'll be a
  loop-breaker because df_i isn't), op1_i will ironically never be
  inlined.  But this is OK: the recursion breaking happens by way of
  a RULE (the magic ClassOp rule above), and RULES work inside stable
  unfoldings. See Note [RULEs enabled in InitialPhase] in GHC.Core.Opt.Simplify.Utils

Note [ClassOp/DFun selection]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
One thing we see a lot is stuff like
    op2 (df d1 d2)
where 'op2' is a ClassOp and 'df' is DFun.  Now, we could inline *both*
'op2' and 'df' to get
     case (MkD ($cop1 d1 d2) ($cop2 d1 d2) ... of
       MkD _ op2 _ _ _ -> op2
And that will reduce to ($cop2 d1 d2) which is what we wanted.

But it's tricky to make this work in practice, because it requires us to
inline both 'op2' and 'df'.  But neither is keen to inline without having
seen the other's result; and it's very easy to get code bloat (from the
big intermediate) if you inline a bit too much.

Instead we use a cunning trick.
 * We arrange that 'df' and 'op2' NEVER inline.

 * We arrange that 'df' is ALWAYS defined in the sylised form
      df d1 d2 = MkD ($cop1 d1 d2) ($cop2 d1 d2) ...

 * We give 'df' a magical unfolding (DFunUnfolding [$cop1, $cop2, ..])
   that lists its methods.

 * We make GHC.Core.Unfold.exprIsConApp_maybe spot a DFunUnfolding and return
   a suitable constructor application -- inlining df "on the fly" as it
   were.

 * ClassOp rules: We give the ClassOp 'op2' a BuiltinRule that
   extracts the right piece iff its argument satisfies
   exprIsConApp_maybe.  This is done in GHC.Types.Id.Make.mkDictSelId

 * We make 'df' CONLIKE, so that shared uses still match; eg
      let d = df d1 d2
      in ...(op2 d)...(op1 d)...

Note [Single-method classes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the class has just one method (or, more accurately, just one element
of {superclasses + methods}), then we use a different strategy.

   class C a where op :: a -> a
   instance C a => C [a] where op = <blah>

We translate the class decl into a newtype, which just gives a
top-level axiom. The "constructor" MkC expands to a cast, as does the
class-op selector.

   axiom Co:C a :: C a ~ (a->a)

   op :: forall a. C a -> (a -> a)
   op a d = d |> (Co:C a)

   MkC :: forall a. (a->a) -> C a
   MkC = /\a.\op. op |> (sym Co:C a)

The clever RULE stuff doesn't work now, because ($df a d) isn't
a constructor application, so exprIsConApp_maybe won't return
Just <blah>.

Instead, we simply rely on the fact that casts are cheap:

   $df :: forall a. C a => C [a]
   {-# INLINE df #-}  -- NB: INLINE this
   $df = /\a. \d. MkC [a] ($cop_list a d)
       = $cop_list |> forall a. C a -> (sym (Co:C [a]))

   $cop_list :: forall a. C a => [a] -> [a]
   $cop_list = <blah>

So if we see
   (op ($df a d))
we'll inline 'op' and '$df', since both are simply casts, and
good things happen.

Why do we use this different strategy?  Because otherwise we
end up with non-inlined dictionaries that look like
    $df = $cop |> blah
which adds an extra indirection to every use, which seems stupid.  See
#4138 for an example (although the regression reported there
wasn't due to the indirection).

There is an awkward wrinkle though: we want to be very
careful when we have
    instance C a => C [a] where
      {-# INLINE op #-}
      op = ...
then we'll get an INLINE pragma on $cop_list but it's important that
$cop_list only inlines when it's applied to *two* arguments (the
dictionary and the list argument).  So we must not eta-expand $df
above.  We ensure that this doesn't happen by putting an INLINE
pragma on the dfun itself; after all, it ends up being just a cast.

There is one more dark corner to the INLINE story, even more deeply
buried.  Consider this (#3772):

    class DeepSeq a => C a where
      gen :: Int -> a

    instance C a => C [a] where
      gen n = ...

    class DeepSeq a where
      deepSeq :: a -> b -> b

    instance DeepSeq a => DeepSeq [a] where
      {-# INLINE deepSeq #-}
      deepSeq xs b = foldr deepSeq b xs

That gives rise to these defns:

    $cdeepSeq :: DeepSeq a -> [a] -> b -> b
    -- User INLINE( 3 args )!
    $cdeepSeq a (d:DS a) b (x:[a]) (y:b) = ...

    $fDeepSeq[] :: DeepSeq a -> DeepSeq [a]
    -- DFun (with auto INLINE pragma)
    $fDeepSeq[] a d = $cdeepSeq a d |> blah

    $cp1 a d :: C a => DeepSep [a]
    -- We don't want to eta-expand this, lest
    -- $cdeepSeq gets inlined in it!
    $cp1 a d = $fDeepSep[] a (scsel a d)

    $fC[] :: C a => C [a]
    -- Ordinary DFun
    $fC[] a d = MkC ($cp1 a d) ($cgen a d)

Here $cp1 is the code that generates the superclass for C [a].  The
issue is this: we must not eta-expand $cp1 either, or else $fDeepSeq[]
and then $cdeepSeq will inline there, which is definitely wrong.  Like
on the dfun, we solve this by adding an INLINE pragma to $cp1.

Note [Subtle interaction of recursion and overlap]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this
  class C a where { op1,op2 :: a -> a }
  instance C a => C [a] where
    op1 x = op2 x ++ op2 x
    op2 x = ...
  instance C [Int] where
    ...

When type-checking the C [a] instance, we need a C [a] dictionary (for
the call of op2).  If we look up in the instance environment, we find
an overlap.  And in *general* the right thing is to complain (see Note
[Overlapping instances] in GHC.Core.InstEnv).  But in *this* case it's wrong to
complain, because we just want to delegate to the op2 of this same
instance.

Why is this justified?  Because we generate a (C [a]) constraint in
a context in which 'a' cannot be instantiated to anything that matches
other overlapping instances, or else we would not be executing this
version of op1 in the first place.

It might even be a bit disguised:

  nullFail :: C [a] => [a] -> [a]
  nullFail x = op2 x ++ op2 x

  instance C a => C [a] where
    op1 x = nullFail x

Precisely this is used in package 'regex-base', module Context.hs.
See the overlapping instances for RegexContext, and the fact that they
call 'nullFail' just like the example above.  The DoCon package also
does the same thing; it shows up in module Fraction.hs.

Conclusion: when typechecking the methods in a C [a] instance, we want to
treat the 'a' as an *existential* type variable, in the sense described
by Note [Binding when looking up instances].  That is why isOverlappableTyVar
responds True to an InstSkol, which is the kind of skolem we use in
tcInstDecl2.


Note [Tricky type variable scoping]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In our example
        class C a where
           op1, op2 :: Ix b => a -> b -> b
           op2 = <dm-rhs>

        instance C a => C [a]
           {-# INLINE [2] op1 #-}
           op1 = <rhs>

note that 'a' and 'b' are *both* in scope in <dm-rhs>, but only 'a' is
in scope in <rhs>.  In particular, we must make sure that 'b' is in
scope when typechecking <dm-rhs>.  This is achieved by subFunTys,
which brings appropriate tyvars into scope. This happens for both
<dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
complained if 'b' is mentioned in <rhs>.



************************************************************************
*                                                                      *
\subsection{Extracting instance decls}
*                                                                      *
************************************************************************

Gather up the instance declarations from their various sources
-}

tcInstDecls1    -- Deal with both source-code and imported instance decls
   :: [LInstDecl GhcRn]         -- Source code instance decls
   -> TcM (TcGblEnv,            -- The full inst env
           [InstInfo GhcRn],    -- Source-code instance decls to process;
                                -- contains all dfuns for this module
           [DerivInfo],         -- From data family instances
           ThBindEnv)           -- TH binding levels

tcInstDecls1 :: [LInstDecl GhcRn]
-> TcM (TcGblEnv, [InstInfo GhcRn], [DerivInfo], ThBindEnv)
tcInstDecls1 [LInstDecl GhcRn]
inst_decls
  = do {    -- Do class and family instance declarations
       ; stuff <- (GenLocated SrcSpanAnnA (InstDecl GhcRn)
 -> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo]))
-> [GenLocated SrcSpanAnnA (InstDecl GhcRn)]
-> TcRn [([InstInfo GhcRn], [FamInst], [DerivInfo])]
forall a b. (a -> TcRn b) -> [a] -> TcRn [b]
mapAndRecoverM LInstDecl GhcRn -> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
GenLocated SrcSpanAnnA (InstDecl GhcRn)
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
tcLocalInstDecl [LInstDecl GhcRn]
[GenLocated SrcSpanAnnA (InstDecl GhcRn)]
inst_decls

       ; let (local_infos_s, fam_insts_s, datafam_deriv_infos) = unzip3 stuff
             fam_insts   = [[FamInst]] -> [FamInst]
forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[FamInst]]
fam_insts_s
             local_infos = [[InstInfo GhcRn]] -> [InstInfo GhcRn]
forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[InstInfo GhcRn]]
local_infos_s

       ; (gbl_env, th_bndrs) <-
           addClsInsts local_infos $
           addFamInsts fam_insts

       ; return ( gbl_env
                , local_infos
                , concat datafam_deriv_infos
                , th_bndrs ) }

-- | Use DerivInfo for data family instances (produced by tcInstDecls1),
--   datatype declarations (TyClDecl), and standalone deriving declarations
--   (DerivDecl) to check and process all derived class instances.
tcInstDeclsDeriv
  :: [DerivInfo]
  -> [LDerivDecl GhcRn]
  -> TcM (TcGblEnv, [InstInfo GhcRn], HsValBinds GhcRn)
tcInstDeclsDeriv :: [DerivInfo]
-> [LDerivDecl GhcRn]
-> TcM (TcGblEnv, [InstInfo GhcRn], HsValBinds GhcRn)
tcInstDeclsDeriv [DerivInfo]
deriv_infos [LDerivDecl GhcRn]
derivds
  = do th_stage <- TcM ThStage
getStage -- See Note [Deriving inside TH brackets]
       if isBrackStage th_stage
       then do { gbl_env <- getGblEnv
               ; return (gbl_env, bagToList emptyBag, emptyValBindsOut) }
       else do { (tcg_env, info_bag, valbinds) <- tcDeriving deriv_infos derivds
               ; return (tcg_env, bagToList info_bag, valbinds) }

addClsInsts :: [InstInfo GhcRn] -> TcM a -> TcM a
addClsInsts :: forall a. [InstInfo GhcRn] -> TcM a -> TcM a
addClsInsts [InstInfo GhcRn]
infos TcM a
thing_inside
  = [ClsInst] -> TcM a -> TcM a
forall a. [ClsInst] -> TcM a -> TcM a
tcExtendLocalInstEnv ((InstInfo GhcRn -> ClsInst) -> [InstInfo GhcRn] -> [ClsInst]
forall a b. (a -> b) -> [a] -> [b]
map InstInfo GhcRn -> ClsInst
forall a. InstInfo a -> ClsInst
iSpec [InstInfo GhcRn]
infos) TcM a
thing_inside

addFamInsts :: [FamInst] -> TcM (TcGblEnv, ThBindEnv)
-- Extend (a) the family instance envt
--        (b) the type envt with stuff from data type decls
addFamInsts :: [FamInst] -> TcM (TcGblEnv, ThBindEnv)
addFamInsts [FamInst]
fam_insts
  = [FamInst] -> TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv)
forall a. [FamInst] -> TcM a -> TcM a
tcExtendLocalFamInstEnv [FamInst]
fam_insts (TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv))
-> TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv)
forall a b. (a -> b) -> a -> b
$
    [TyThing] -> TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv)
forall r. [TyThing] -> TcM r -> TcM r
tcExtendGlobalEnv [TyThing]
axioms          (TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv))
-> TcM (TcGblEnv, ThBindEnv) -> TcM (TcGblEnv, ThBindEnv)
forall a b. (a -> b) -> a -> b
$
    do { String -> SDoc -> TcRn ()
traceTc String
"addFamInsts" ([FamInst] -> SDoc
pprFamInsts [FamInst]
fam_insts)
       ; (gbl_env, th_bndrs) <- [TyCon] -> TcM (TcGblEnv, ThBindEnv)
addTyConsToGblEnv [TyCon]
data_rep_tycons
                    -- Does not add its axiom; that comes
                    -- from adding the 'axioms' above
       ; return (gbl_env, th_bndrs)
       }
  where
    axioms :: [TyThing]
axioms = (FamInst -> TyThing) -> [FamInst] -> [TyThing]
forall a b. (a -> b) -> [a] -> [b]
map (CoAxiom Branched -> TyThing
ACoAxiom (CoAxiom Branched -> TyThing)
-> (FamInst -> CoAxiom Branched) -> FamInst -> TyThing
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CoAxiom Unbranched -> CoAxiom Branched
forall (br :: BranchFlag). CoAxiom br -> CoAxiom Branched
toBranchedAxiom (CoAxiom Unbranched -> CoAxiom Branched)
-> (FamInst -> CoAxiom Unbranched) -> FamInst -> CoAxiom Branched
forall b c a. (b -> c) -> (a -> b) -> a -> c
. FamInst -> CoAxiom Unbranched
famInstAxiom) [FamInst]
fam_insts
    data_rep_tycons :: [TyCon]
data_rep_tycons = [FamInst] -> [TyCon]
famInstsRepTyCons [FamInst]
fam_insts
      -- The representation tycons for 'data instances' declarations

{-
Note [Deriving inside TH brackets]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Given a declaration bracket
  [d| data T = A | B deriving( Show ) |]

there is really no point in generating the derived code for deriving(
Show) and then type-checking it. This will happen at the call site
anyway, and the type check should never fail!  Moreover (#6005)
the scoping of the generated code inside the bracket does not seem to
work out.

The easy solution is simply not to generate the derived instances at
all.  (A less brutal solution would be to generate them with no
bindings.)  This will become moot when we shift to the new TH plan, so
the brutal solution will do.
-}

tcLocalInstDecl :: LInstDecl GhcRn
                -> TcM ([InstInfo GhcRn], [FamInst], [DerivInfo])
        -- A source-file instance declaration
        -- Type-check all the stuff before the "where"
        --
        -- We check for respectable instance type, and context
tcLocalInstDecl :: LInstDecl GhcRn -> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
tcLocalInstDecl (L SrcSpanAnnA
loc (TyFamInstD { tfid_inst :: forall pass. InstDecl pass -> TyFamInstDecl pass
tfid_inst = TyFamInstDecl GhcRn
decl }))
  = do { fam_inst <- AssocInstInfo -> LTyFamInstDecl GhcRn -> TcM FamInst
tcTyFamInstDecl AssocInstInfo
NotAssociated (SrcSpanAnnA
-> TyFamInstDecl GhcRn
-> GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc TyFamInstDecl GhcRn
decl)
       ; return ([], [fam_inst], []) }

tcLocalInstDecl (L SrcSpanAnnA
loc (DataFamInstD { dfid_inst :: forall pass. InstDecl pass -> DataFamInstDecl pass
dfid_inst = DataFamInstDecl GhcRn
decl }))
  = do { (fam_inst, m_deriv_info) <- AssocInstInfo
-> TyVarEnv Name
-> LDataFamInstDecl GhcRn
-> TcM (FamInst, Maybe DerivInfo)
tcDataFamInstDecl AssocInstInfo
NotAssociated TyVarEnv Name
forall a. VarEnv a
emptyVarEnv (SrcSpanAnnA
-> DataFamInstDecl GhcRn
-> GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc DataFamInstDecl GhcRn
decl)
       ; return ([], [fam_inst], maybeToList m_deriv_info) }

tcLocalInstDecl (L SrcSpanAnnA
loc (ClsInstD { cid_inst :: forall pass. InstDecl pass -> ClsInstDecl pass
cid_inst = ClsInstDecl GhcRn
decl }))
  = do { (insts, fam_insts, deriv_infos) <- LClsInstDecl GhcRn
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
tcClsInstDecl (SrcSpanAnnA
-> ClsInstDecl GhcRn -> GenLocated SrcSpanAnnA (ClsInstDecl GhcRn)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc ClsInstDecl GhcRn
decl)
       ; return (insts, fam_insts, deriv_infos) }

tcClsInstDecl :: LClsInstDecl GhcRn
              -> TcM ([InstInfo GhcRn], [FamInst], [DerivInfo])
-- The returned DerivInfos are for any associated data families
tcClsInstDecl :: LClsInstDecl GhcRn
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
tcClsInstDecl (L SrcSpanAnnA
loc (ClsInstDecl { cid_ext :: forall pass. ClsInstDecl pass -> XCClsInstDecl pass
cid_ext = XCClsInstDecl GhcRn
lwarn
                                  , cid_poly_ty :: forall pass. ClsInstDecl pass -> LHsSigType pass
cid_poly_ty = LHsSigType GhcRn
hs_ty, cid_binds :: forall pass. ClsInstDecl pass -> LHsBinds pass
cid_binds = LHsBinds GhcRn
binds
                                  , cid_sigs :: forall pass. ClsInstDecl pass -> [LSig pass]
cid_sigs = [LSig GhcRn]
uprags, cid_tyfam_insts :: forall pass. ClsInstDecl pass -> [LTyFamInstDecl pass]
cid_tyfam_insts = [LTyFamInstDecl GhcRn]
ats
                                  , cid_overlap_mode :: forall pass. ClsInstDecl pass -> Maybe (XRec pass OverlapMode)
cid_overlap_mode = Maybe (XRec GhcRn OverlapMode)
overlap_mode
                                  , cid_datafam_insts :: forall pass. ClsInstDecl pass -> [LDataFamInstDecl pass]
cid_datafam_insts = [LDataFamInstDecl GhcRn]
adts }))
  = SrcSpanAnnA
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
forall ann a. EpAnn ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc                   (TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
 -> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo]))
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
forall a b. (a -> b) -> a -> b
$
    ErrCtxtMsg
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
forall a. ErrCtxtMsg -> TcM a -> TcM a
addErrCtxt (LHsSigType GhcRn -> ErrCtxtMsg
instDeclCtxt1 LHsSigType GhcRn
hs_ty)  (TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
 -> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo]))
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
-> TcRn ([InstInfo GhcRn], [FamInst], [DerivInfo])
forall a b. (a -> b) -> a -> b
$
    do  { dfun_ty <- UserTypeCtxt -> LHsSigType GhcRn -> TcM Type
tcHsClsInstType (Bool -> UserTypeCtxt
InstDeclCtxt Bool
False) LHsSigType GhcRn
hs_ty
        ; let (tyvars, theta, clas, inst_tys) = tcSplitDFunTy dfun_ty
             -- NB: tcHsClsInstType does checkValidInstance
        ; skol_info <- mkSkolemInfo (mkClsInstSkol clas inst_tys)
        ; (subst, skol_tvs) <- tcInstSkolTyVars skol_info tyvars
        ; let tv_skol_prs = [ (Id -> Name
tyVarName Id
tv, Id
skol_tv)
                            | (Id
tv, Id
skol_tv) <- [Id]
tyvars [Id] -> [Id] -> [(Id, Id)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Id]
skol_tvs ]
              -- Map from the skolemized Names to the original Names.
              -- See Note [Associated data family instances and di_scoped_tvs].
              tv_skol_env = [(Id, Name)] -> TyVarEnv Name
forall a. [(Id, a)] -> VarEnv a
mkVarEnv ([(Id, Name)] -> TyVarEnv Name) -> [(Id, Name)] -> TyVarEnv Name
forall a b. (a -> b) -> a -> b
$ ((Name, Id) -> (Id, Name)) -> [(Name, Id)] -> [(Id, Name)]
forall a b. (a -> b) -> [a] -> [b]
map (Name, Id) -> (Id, Name)
forall a b. (a, b) -> (b, a)
swap [(Name, Id)]
tv_skol_prs
              n_inferred = (ForAllTyBinder -> Bool) -> [ForAllTyBinder] -> Int
forall a. (a -> Bool) -> [a] -> Int
countWhile ((ForAllTyFlag -> ForAllTyFlag -> Bool
forall a. Eq a => a -> a -> Bool
== ForAllTyFlag
Inferred) (ForAllTyFlag -> Bool)
-> (ForAllTyBinder -> ForAllTyFlag) -> ForAllTyBinder -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ForAllTyBinder -> ForAllTyFlag
forall tv argf. VarBndr tv argf -> argf
binderFlag) ([ForAllTyBinder] -> Int) -> [ForAllTyBinder] -> Int
forall a b. (a -> b) -> a -> b
$
                           ([ForAllTyBinder], Type) -> [ForAllTyBinder]
forall a b. (a, b) -> a
fst (([ForAllTyBinder], Type) -> [ForAllTyBinder])
-> ([ForAllTyBinder], Type) -> [ForAllTyBinder]
forall a b. (a -> b) -> a -> b
$ Type -> ([ForAllTyBinder], Type)
splitForAllForAllTyBinders Type
dfun_ty
              visible_skol_tvs = Int -> [Id] -> [Id]
forall a. Int -> [a] -> [a]
drop Int
n_inferred [Id]
skol_tvs

        ; traceTc "tcLocalInstDecl 1" (ppr dfun_ty $$ ppr (invisibleBndrCount dfun_ty) $$ ppr skol_tvs)

        -- Next, process any associated types.
        ; (datafam_stuff, tyfam_insts)
             <- tcExtendNameTyVarEnv tv_skol_prs $
                do  { let mini_env   = [(Id, Type)] -> VarEnv Type
forall a. [(Id, a)] -> VarEnv a
mkVarEnv (Class -> [Id]
classTyVars Class
clas [Id] -> [Type] -> [(Id, Type)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` HasDebugCallStack => Subst -> [Type] -> [Type]
Subst -> [Type] -> [Type]
substTys Subst
subst [Type]
inst_tys)
                          mini_subst = InScopeSet -> VarEnv Type -> Subst
mkTvSubst (VarSet -> InScopeSet
mkInScopeSet ([Id] -> VarSet
mkVarSet [Id]
skol_tvs)) VarEnv Type
mini_env
                          mb_info    = InClsInst { ai_class :: Class
ai_class = Class
clas
                                                 , ai_tyvars :: [Id]
ai_tyvars = [Id]
visible_skol_tvs
                                                 , ai_inst_env :: VarEnv Type
ai_inst_env = VarEnv Type
mini_env }
                    ; df_stuff  <- mapAndRecoverM (tcDataFamInstDecl mb_info tv_skol_env) adts
                    ; tf_insts1 <- mapAndRecoverM (tcTyFamInstDecl mb_info)   ats

                      -- Check for missing associated types and build them
                      -- from their defaults (if available)
                    ; is_boot <- tcIsHsBootOrSig
                    ; let atItems = Class -> [ClassATItem]
classATItems Class
clas
                    ; tf_insts2 <- mapM (tcATDefault (locA loc) mini_subst defined_ats)
                                        (if is_boot then [] else atItems)
                      -- Don't default type family instances, but rather omit, in hsig/hs-boot.
                      -- Since hsig/hs-boot files are essentially large binders we want omission
                      -- of the definition to result in no restriction, rather than for example
                      -- attempting to "pattern match" with the invisible defaults and generate
                      -- equalities. Without further handling, this would just result in a panic
                      -- anyway.
                      -- See https://github.com/ghc-proposals/ghc-proposals/pull/320 for
                      -- additional discussion.
                    ; return (df_stuff, tf_insts1 ++ concat tf_insts2) }


        -- Finally, construct the Core representation of the instance.
        -- (This no longer includes the associated types.)
        ; dfun_name <- newDFunName clas inst_tys (getLocA hs_ty)
                -- Dfun location is that of instance *header*

        ; let warn = (GenLocated SrcSpanAnnP (WarningTxt GhcRn) -> WarningTxt GhcRn)
-> Maybe (GenLocated SrcSpanAnnP (WarningTxt GhcRn))
-> Maybe (WarningTxt GhcRn)
forall a b. (a -> b) -> Maybe a -> Maybe b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap GenLocated SrcSpanAnnP (WarningTxt GhcRn) -> WarningTxt GhcRn
forall l e. GenLocated l e -> e
unLoc Maybe (GenLocated SrcSpanAnnP (WarningTxt GhcRn))
XCClsInstDecl GhcRn
lwarn
        ; ispec <- newClsInst (fmap unLoc overlap_mode) dfun_name
                              tyvars theta clas inst_tys warn

        ; let inst_binds = InstBindings
                             { ib_binds :: LHsBinds GhcRn
ib_binds = LHsBinds GhcRn
binds
                             , ib_tyvars :: [Name]
ib_tyvars = (Id -> Name) -> [Id] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map Id -> Name
Var.varName [Id]
tyvars -- Scope over bindings
                             , ib_pragmas :: [LSig GhcRn]
ib_pragmas = [LSig GhcRn]
uprags
                             , ib_extensions :: [Extension]
ib_extensions = []
                             , ib_derived :: Bool
ib_derived = Bool
False }
              inst_info = InstInfo { iSpec :: ClsInst
iSpec  = ClsInst
ispec, iBinds :: InstBindings GhcRn
iBinds = InstBindings GhcRn
inst_binds }

              (datafam_insts, m_deriv_infos) = unzip datafam_stuff
              deriv_infos                    = [Maybe DerivInfo] -> [DerivInfo]
forall a. [Maybe a] -> [a]
catMaybes [Maybe DerivInfo]
m_deriv_infos
              all_insts                      = [FamInst]
tyfam_insts [FamInst] -> [FamInst] -> [FamInst]
forall a. [a] -> [a] -> [a]
++ [FamInst]
datafam_insts

         -- In hs-boot files there should be no bindings
        ; gbl_env <- getGblEnv;
        ; case tcg_src gbl_env of
          { HscSource
HsSrcFile -> () -> TcRn ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()
          ; HsBootOrSig HsBootOrSig
boot_or_sig ->
             do { HsBootOrSig
-> (NonEmpty (GenLocated SrcSpanAnnA (HsBind GhcRn))
    -> BadBootDecls)
-> [GenLocated SrcSpanAnnA (HsBind GhcRn)]
-> TcRn ()
forall decl.
HsBootOrSig
-> (NonEmpty (LocatedA decl) -> BadBootDecls)
-> [LocatedA decl]
-> TcRn ()
rejectBootDecls HsBootOrSig
boot_or_sig NonEmpty (LHsBindLR GhcRn GhcRn) -> BadBootDecls
NonEmpty (GenLocated SrcSpanAnnA (HsBind GhcRn)) -> BadBootDecls
BootBindsRn LHsBinds GhcRn
[GenLocated SrcSpanAnnA (HsBind GhcRn)]
binds
                ; HsBootOrSig
-> (NonEmpty (GenLocated SrcSpanAnnA (Sig GhcRn)) -> BadBootDecls)
-> [GenLocated SrcSpanAnnA (Sig GhcRn)]
-> TcRn ()
forall decl.
HsBootOrSig
-> (NonEmpty (LocatedA decl) -> BadBootDecls)
-> [LocatedA decl]
-> TcRn ()
rejectBootDecls HsBootOrSig
boot_or_sig NonEmpty (LSig GhcRn) -> BadBootDecls
NonEmpty (GenLocated SrcSpanAnnA (Sig GhcRn)) -> BadBootDecls
BootInstanceSigs [LSig GhcRn]
[GenLocated SrcSpanAnnA (Sig GhcRn)]
uprags } }
        ; return ([inst_info], all_insts, deriv_infos) }
  where
    defined_ats :: NameSet
defined_ats = [Name] -> NameSet
mkNameSet ((GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn) -> Name)
-> [GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn)] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map (TyFamInstDecl GhcRn -> IdP GhcRn
TyFamInstDecl GhcRn -> Name
forall (p :: Pass).
(Anno (IdGhcP p) ~ SrcSpanAnnN) =>
TyFamInstDecl (GhcPass p) -> IdP (GhcPass p)
tyFamInstDeclName (TyFamInstDecl GhcRn -> Name)
-> (GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn)
    -> TyFamInstDecl GhcRn)
-> GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn)
-> Name
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn) -> TyFamInstDecl GhcRn
forall l e. GenLocated l e -> e
unLoc) [LTyFamInstDecl GhcRn]
[GenLocated SrcSpanAnnA (TyFamInstDecl GhcRn)]
ats)
                  NameSet -> NameSet -> NameSet
`unionNameSet`
                  [Name] -> NameSet
mkNameSet ((GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn) -> Name)
-> [GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map (GenLocated SrcSpanAnnN Name -> Name
forall l e. GenLocated l e -> e
unLoc (GenLocated SrcSpanAnnN Name -> Name)
-> (GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
    -> GenLocated SrcSpanAnnN Name)
-> GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
-> Name
forall b c a. (b -> c) -> (a -> b) -> a -> c
. FamEqn GhcRn (HsDataDefn GhcRn) -> LIdP GhcRn
FamEqn GhcRn (HsDataDefn GhcRn) -> GenLocated SrcSpanAnnN Name
forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon
                                        (FamEqn GhcRn (HsDataDefn GhcRn) -> GenLocated SrcSpanAnnN Name)
-> (GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
    -> FamEqn GhcRn (HsDataDefn GhcRn))
-> GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
-> GenLocated SrcSpanAnnN Name
forall b c a. (b -> c) -> (a -> b) -> a -> c
. DataFamInstDecl GhcRn -> FamEqn GhcRn (HsDataDefn GhcRn)
forall pass. DataFamInstDecl pass -> FamEqn pass (HsDataDefn pass)
dfid_eqn
                                        (DataFamInstDecl GhcRn -> FamEqn GhcRn (HsDataDefn GhcRn))
-> (GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
    -> DataFamInstDecl GhcRn)
-> GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
-> FamEqn GhcRn (HsDataDefn GhcRn)
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)
-> DataFamInstDecl GhcRn
forall l e. GenLocated l e -> e
unLoc) [LDataFamInstDecl GhcRn]
[GenLocated SrcSpanAnnA (DataFamInstDecl GhcRn)]
adts)

{-
************************************************************************
*                                                                      *
               Type family instances
*                                                                      *
************************************************************************

Family instances are somewhat of a hybrid.  They are processed together with
class instance heads, but can contain data constructors and hence they share a
lot of kinding and type checking code with ordinary algebraic data types (and
GADTs).
-}

tcTyFamInstDecl :: AssocInstInfo
                -> LTyFamInstDecl GhcRn -> TcM FamInst
  -- "type instance"; open type families only
  -- See Note [Associated type instances]
tcTyFamInstDecl :: AssocInstInfo -> LTyFamInstDecl GhcRn -> TcM FamInst
tcTyFamInstDecl AssocInstInfo
mb_clsinfo (L SrcSpanAnnA
loc decl :: TyFamInstDecl GhcRn
decl@(TyFamInstDecl { tfid_eqn :: forall pass. TyFamInstDecl pass -> TyFamInstEqn pass
tfid_eqn = TyFamInstEqn GhcRn
eqn }))
  = SrcSpanAnnA -> TcM FamInst -> TcM FamInst
forall ann a. EpAnn ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc                        (TcM FamInst -> TcM FamInst) -> TcM FamInst -> TcM FamInst
forall a b. (a -> b) -> a -> b
$
    AssocInstInfo -> TyFamInstDecl GhcRn -> TcM FamInst -> TcM FamInst
forall a. AssocInstInfo -> TyFamInstDecl GhcRn -> TcM a -> TcM a
tcAddOpenTyFamInstCtxt AssocInstInfo
mb_clsinfo TyFamInstDecl GhcRn
decl (TcM FamInst -> TcM FamInst) -> TcM FamInst -> TcM FamInst
forall a b. (a -> b) -> a -> b
$
    do { let fam_lname :: LIdP GhcRn
fam_lname = FamEqn GhcRn (GenLocated SrcSpanAnnA (HsType GhcRn)) -> LIdP GhcRn
forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon TyFamInstEqn GhcRn
FamEqn GhcRn (GenLocated SrcSpanAnnA (HsType GhcRn))
eqn
       ; fam_tc <- GenLocated SrcSpanAnnN Name -> TcM TyCon
tcLookupLocatedTyCon LIdP GhcRn
GenLocated SrcSpanAnnN Name
fam_lname
       ; tcFamInstDeclChecks mb_clsinfo IAmType fam_tc

         -- (0) Check it's an open type family
       ; checkTc (isTypeFamilyTyCon fam_tc) $
           TcRnIllegalInstance $ IllegalFamilyInstance $
             FamilyCategoryMismatch fam_tc
       ; checkTc (isOpenTypeFamilyTyCon fam_tc) $
           TcRnIllegalInstance $ IllegalFamilyInstance $
             NotAnOpenFamilyTyCon fam_tc

         -- (1) do the work of verifying the synonym group
         -- For some reason we don't have a location for the equation
         -- itself, so we make do with the location of family name
       ; (co_ax_branch, co_ax_validity_info)
          <- tcTyFamInstEqn fam_tc mb_clsinfo
                (L (l2l $ getLoc fam_lname) eqn)

         -- (2) check for validity
       ; checkConsistentFamInst mb_clsinfo fam_tc co_ax_branch
       ; checkTyFamEqnValidityInfo fam_tc co_ax_validity_info
       ; checkValidCoAxBranch fam_tc co_ax_branch

         -- (3) construct coercion axiom
       ; rep_tc_name <- newFamInstAxiomName fam_lname [coAxBranchLHS co_ax_branch]
       ; let axiom = Name -> TyCon -> KnotTied CoAxBranch -> CoAxiom Unbranched
mkUnbranchedCoAxiom Name
rep_tc_name TyCon
fam_tc KnotTied CoAxBranch
co_ax_branch
       ; newFamInst SynFamilyInst axiom }


---------------------
tcFamInstDeclChecks :: AssocInstInfo -> TypeOrData -> TyCon -> TcM ()
-- Used for both type and data families
tcFamInstDeclChecks :: AssocInstInfo -> TypeOrData -> TyCon -> TcRn ()
tcFamInstDeclChecks AssocInstInfo
mb_clsinfo TypeOrData
ty_or_data TyCon
fam_tc
  = do { -- Type family instances require -XTypeFamilies
         -- and can't (currently) be in an hs-boot file
       ; String -> SDoc -> TcRn ()
traceTc String
"tcFamInstDecl" (TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc)
       ; type_families <- Extension -> TcRn Bool
forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.TypeFamilies
       ; hs_src        <- tcHscSource   -- Are we compiling an hs-boot file?
       ; checkTc type_families (TcRnTyFamsDisabled (TyFamsDisabledInstance fam_tc))
       ; case hs_src of
           HsBootOrSig HsBootOrSig
boot_or_sig ->
             TcRnMessage -> TcRn ()
addErrTc (TcRnMessage -> TcRn ()) -> TcRnMessage -> TcRn ()
forall a b. (a -> b) -> a -> b
$ HsBootOrSig -> BadBootDecls -> TcRnMessage
TcRnIllegalHsBootOrSigDecl HsBootOrSig
boot_or_sig (TyCon -> BadBootDecls
BootFamInst TyCon
fam_tc)
           HscSource
HsSrcFile               ->
             () -> TcRn ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

       -- Check that it is a family TyCon
       ; checkTc (isFamilyTyCon fam_tc) $
          TcRnIllegalInstance $ IllegalFamilyInstance $
            NotAFamilyTyCon ty_or_data fam_tc

       -- Check that top-level type instances are not for associated types.
       ; when (isNotAssociated mb_clsinfo &&   -- Not in a class decl
               isTyConAssoc fam_tc) $          -- but an associated type
          addErr $ TcRnIllegalInstance $ IllegalFamilyInstance
                 $ InvalidAssoc $ InvalidAssocInstance
                 $ AssocInstanceNotInAClass fam_tc
       }

{- Note [Associated type instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We allow this:
  class C a where
    type T x a
  instance C Int where
    type T (S y) Int = y
    type T Z     Int = Char

Note that
  a) The variable 'x' is not bound by the class decl
  b) 'x' is instantiated to a non-type-variable in the instance
  c) There are several type instance decls for T in the instance

All this is fine.  Of course, you can't give any *more* instances
for (T ty Int) elsewhere, because it's an *associated* type.


************************************************************************
*                                                                      *
               Data family instances
*                                                                      *
************************************************************************

For some reason data family instances are a lot more complicated
than type family instances
-}

tcDataFamInstDecl ::
     AssocInstInfo
  -> TyVarEnv Name -- If this is an associated data family instance, maps the
                   -- parent class's skolemized type variables to their
                   -- original Names. If this is a non-associated instance,
                   -- this will be empty.
                   -- See Note [Associated data family instances and di_scoped_tvs].
  -> LDataFamInstDecl GhcRn -> TcM (FamInst, Maybe DerivInfo)
  -- "newtype instance" and "data instance"
tcDataFamInstDecl :: AssocInstInfo
-> TyVarEnv Name
-> LDataFamInstDecl GhcRn
-> TcM (FamInst, Maybe DerivInfo)
tcDataFamInstDecl AssocInstInfo
mb_clsinfo TyVarEnv Name
tv_skol_env
    (L SrcSpanAnnA
loc decl :: DataFamInstDecl GhcRn
decl@(DataFamInstDecl { dfid_eqn :: forall pass. DataFamInstDecl pass -> FamEqn pass (HsDataDefn pass)
dfid_eqn =
      FamEqn { feqn_bndrs :: forall pass rhs. FamEqn pass rhs -> HsOuterFamEqnTyVarBndrs pass
feqn_bndrs  = HsOuterFamEqnTyVarBndrs GhcRn
outer_bndrs
             , feqn_pats :: forall pass rhs. FamEqn pass rhs -> HsFamEqnPats pass
feqn_pats   = HsFamEqnPats GhcRn
hs_pats
             , feqn_tycon :: forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon  = lfam_name :: LIdP GhcRn
lfam_name@(L SrcSpanAnnN
_ Name
fam_name)
             , feqn_fixity :: forall pass rhs. FamEqn pass rhs -> LexicalFixity
feqn_fixity = LexicalFixity
fixity
             , feqn_rhs :: forall pass rhs. FamEqn pass rhs -> rhs
feqn_rhs    = HsDataDefn { dd_cType :: forall pass. HsDataDefn pass -> Maybe (XRec pass CType)
dd_cType   = Maybe (XRec GhcRn CType)
cType
                                        , dd_ctxt :: forall pass. HsDataDefn pass -> Maybe (LHsContext pass)
dd_ctxt    = Maybe (LHsContext GhcRn)
hs_ctxt
                                        , dd_cons :: forall pass. HsDataDefn pass -> DataDefnCons (LConDecl pass)
dd_cons    = DataDefnCons (LConDecl GhcRn)
hs_cons
                                        , dd_kindSig :: forall pass. HsDataDefn pass -> Maybe (LHsKind pass)
dd_kindSig = Maybe (LHsKind GhcRn)
m_ksig
                                        , dd_derivs :: forall pass. HsDataDefn pass -> HsDeriving pass
dd_derivs  = HsDeriving GhcRn
derivs } }}))
  = SrcSpanAnnA
-> TcM (FamInst, Maybe DerivInfo) -> TcM (FamInst, Maybe DerivInfo)
forall ann a. EpAnn ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc                      (TcM (FamInst, Maybe DerivInfo) -> TcM (FamInst, Maybe DerivInfo))
-> TcM (FamInst, Maybe DerivInfo) -> TcM (FamInst, Maybe DerivInfo)
forall a b. (a -> b) -> a -> b
$
    AssocInstInfo
-> NewOrData
-> DataFamInstDecl GhcRn
-> TcM (FamInst, Maybe DerivInfo)
-> TcM (FamInst, Maybe DerivInfo)
forall a.
AssocInstInfo
-> NewOrData -> DataFamInstDecl GhcRn -> TcM a -> TcM a
tcAddDataFamInstCtxt AssocInstInfo
mb_clsinfo NewOrData
new_or_data DataFamInstDecl GhcRn
decl (TcM (FamInst, Maybe DerivInfo) -> TcM (FamInst, Maybe DerivInfo))
-> TcM (FamInst, Maybe DerivInfo) -> TcM (FamInst, Maybe DerivInfo)
forall a b. (a -> b) -> a -> b
$
    do { fam_tc <- GenLocated SrcSpanAnnN Name -> TcM TyCon
tcLookupLocatedTyCon LIdP GhcRn
GenLocated SrcSpanAnnN Name
lfam_name

       ; tcFamInstDeclChecks mb_clsinfo (IAmData new_or_data) fam_tc

       -- Check that the family declaration is for the right kind
       ; checkTc (isDataFamilyTyCon fam_tc) $
          TcRnIllegalInstance $ IllegalFamilyInstance $
            FamilyCategoryMismatch fam_tc
       ; gadt_syntax <- dataDeclChecks fam_name hs_ctxt hs_cons
          -- Do /not/ check that the number of patterns = tyConArity fam_tc
          -- See [Arity of data families] in GHC.Core.FamInstEnv
       ; skol_info <- mkSkolemInfo FamInstSkol
       ; (qtvs, non_user_tvs, pats, tc_res_kind, stupid_theta)
             <- tcDataFamInstHeader mb_clsinfo skol_info fam_tc outer_bndrs fixity
                                    hs_ctxt hs_pats m_ksig hs_cons

       -- Eta-reduce the axiom if possible
       -- Quite tricky: see Note [Implementing eta reduction for data families]
       ; let (eta_pats, eta_tcbs) = eta_reduce fam_tc pats
             eta_tvs       = (TyConBinder -> Id) -> [TyConBinder] -> [Id]
forall a b. (a -> b) -> [a] -> [b]
map TyConBinder -> Id
forall tv argf. VarBndr tv argf -> tv
binderVar [TyConBinder]
eta_tcbs
             post_eta_qtvs = (Id -> Bool) -> [Id] -> [Id]
forall a. (a -> Bool) -> [a] -> [a]
filterOut (Id -> [Id] -> Bool
forall a. Eq a => a -> [a] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Id]
eta_tvs) [Id]
qtvs

             full_tcbs = [Id] -> VarSet -> [TyConBinder]
mkTyConBindersPreferAnon [Id]
post_eta_qtvs
                            (Type -> VarSet
tyCoVarsOfType ([Id] -> Type -> Type
mkSpecForAllTys [Id]
eta_tvs Type
tc_res_kind))
                         [TyConBinder] -> [TyConBinder] -> [TyConBinder]
forall a. [a] -> [a] -> [a]
++ [TyConBinder]
eta_tcbs
                 -- Put the eta-removed tyvars at the end
                 -- Remember, qtvs is in arbitrary order, except kind vars are
                 -- first, so there is no reason to suppose that the eta_tvs
                 -- (obtained from the pats) are at the end (#11148)

       -- Eta-expand the representation tycon until it has result
       -- kind `TYPE r`, for some `r`. If UnliftedNewtypes is not enabled, we
       -- go one step further and ensure that it has kind `TYPE 'LiftedRep`.
       --
       -- See also Note [Arity of data families] in GHC.Core.FamInstEnv
       -- NB: we can do this after eta-reducing the axiom, because if
       --     we did it before the "extra" tvs from etaExpandAlgTyCon
       --     would always be eta-reduced
       --
       ; (extra_tcbs, tc_res_kind) <- etaExpandAlgTyCon skol_info full_tcbs tc_res_kind

       -- Check the result kind; it may come from a user-written signature.
       -- See Note [Datatype return kinds] in GHC.Tc.TyCl point 4(a)
       ; let extra_pats    = (TyConBinder -> Type) -> [TyConBinder] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map (Id -> Type
mkTyVarTy (Id -> Type) -> (TyConBinder -> Id) -> TyConBinder -> Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TyConBinder -> Id
forall tv argf. VarBndr tv argf -> tv
binderVar) [TyConBinder]
extra_tcbs
             all_pats      = [Type]
pats [Type] -> [Type] -> [Type]
forall a. [a] -> [a] -> [a]
`chkAppend` [Type]
extra_pats
             orig_res_ty   = TyCon -> [Type] -> Type
mkTyConApp TyCon
fam_tc [Type]
all_pats
             tc_ty_binders = [TyConBinder]
full_tcbs [TyConBinder] -> [TyConBinder] -> [TyConBinder]
forall a. [a] -> [a] -> [a]
`chkAppend` [TyConBinder]
extra_tcbs

       ; traceTc "tcDataFamInstDecl 1" $
         vcat [ text "Fam tycon:" <+> ppr fam_tc
              , text "Pats:" <+> ppr pats
              , text "visibilities:" <+> ppr (tcbVisibilities fam_tc pats)
              , text "all_pats:" <+> ppr all_pats
              , text "tc_ty_binders" <+> ppr tc_ty_binders
              , text "fam_tc_binders:" <+> ppr (tyConBinders fam_tc)
              , text "tc_res_kind:" <+> ppr tc_res_kind
              , text "eta_pats" <+> ppr eta_pats
              , text "eta_tcbs" <+> ppr eta_tcbs ]

       -- Zonk the patterns etc into the Type world
       ; (ty_binders, res_kind, all_pats, eta_pats, stupid_theta,
           zonked_post_eta_qtvs, zonked_eta_tvs) <-
         initZonkEnv NoFlexi $
         runZonkBndrT (zonkTyVarBindersX tc_ty_binders) $ \ [TyConBinder]
ty_binders ->
           do { res_kind             <- Type -> ZonkTcM Type
zonkTcTypeToTypeX   Type
tc_res_kind
              ; all_pats             <- zonkTcTypesToTypesX all_pats
              ; eta_pats             <- zonkTcTypesToTypesX eta_pats
              ; stupid_theta         <- zonkTcTypesToTypesX stupid_theta
              ; zonked_post_eta_qtvs <- mapM lookupTyVarX   post_eta_qtvs
              ; zonked_eta_tvs       <- mapM lookupTyVarX   eta_tvs
                    -- All these qtvs are in ty_binders, and hence will be in
                    -- the ZonkEnv, ze.  We need the zonked (TyVar) versions to
                    -- put in the CoAxiom that we are about to build.
              ; return (ty_binders, res_kind, all_pats, eta_pats, stupid_theta,
                         zonked_post_eta_qtvs, zonked_eta_tvs) }

       ; traceTc "tcDataFamInstDecl" $
         vcat [ text "Fam tycon:" <+> ppr fam_tc
              , text "Pats:" <+> ppr pats
              , text "visibilities:" <+> ppr (tcbVisibilities fam_tc pats)
              , text "all_pats:" <+> ppr all_pats
              , text "ty_binders" <+> ppr ty_binders
              , text "fam_tc_binders:" <+> ppr (tyConBinders fam_tc)
              , text "res_kind:" <+> ppr res_kind
              , text "eta_pats" <+> ppr eta_pats
              , text "eta_tcbs" <+> ppr eta_tcbs ]
       ; (rep_tc, (axiom, ax_rhs)) <- fixM $ \ ~(TyCon
rec_rep_tc, (CoAxiom Unbranched, Type)
_) ->
           do { data_cons <- [Id] -> TcM (DataDefnCons DataCon) -> TcM (DataDefnCons DataCon)
forall r. [Id] -> TcM r -> TcM r
tcExtendTyVarEnv ([TyConBinder] -> [Id]
forall tv argf. [VarBndr tv argf] -> [tv]
binderVars [TyConBinder]
tc_ty_binders) (TcM (DataDefnCons DataCon) -> TcM (DataDefnCons DataCon))
-> TcM (DataDefnCons DataCon) -> TcM (DataDefnCons DataCon)
forall a b. (a -> b) -> a -> b
$
                  -- For H98 decls, the tyvars scope
                  -- over the data constructors
                  DataDeclInfo
-> TyCon
-> [TyConBinder]
-> Type
-> DataDefnCons (LConDecl GhcRn)
-> TcM (DataDefnCons DataCon)
tcConDecls (Type -> DataDeclInfo
DDataInstance Type
orig_res_ty) TyCon
rec_rep_tc [TyConBinder]
tc_ty_binders Type
tc_res_kind
                      DataDefnCons (LConDecl GhcRn)
hs_cons

              ; rep_tc_name <- newFamInstTyConName lfam_name pats
              ; axiom_name  <- newFamInstAxiomName lfam_name [pats]
              ; tc_rhs <- case data_cons of
                     DataTypeCons Bool
type_data [DataCon]
data_cons -> AlgTyConRhs -> IOEnv (Env TcGblEnv TcLclEnv) AlgTyConRhs
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (AlgTyConRhs -> IOEnv (Env TcGblEnv TcLclEnv) AlgTyConRhs)
-> AlgTyConRhs -> IOEnv (Env TcGblEnv TcLclEnv) AlgTyConRhs
forall a b. (a -> b) -> a -> b
$
                        Bool -> Bool -> [DataCon] -> AlgTyConRhs
mkLevPolyDataTyConRhs
                          (HasDebugCallStack => Type -> Bool
Type -> Bool
isFixedRuntimeRepKind Type
res_kind)
                          Bool
type_data
                          [DataCon]
data_cons
                     NewTypeCon DataCon
data_con -> Name
-> TyCon -> DataCon -> IOEnv (Env TcGblEnv TcLclEnv) AlgTyConRhs
forall m n. Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
mkNewTyConRhs Name
rep_tc_name TyCon
rec_rep_tc DataCon
data_con

              ; let ax_rhs = TyCon -> [Type] -> Type
mkTyConApp TyCon
rep_tc ([Id] -> [Type]
mkTyVarTys [Id]
zonked_post_eta_qtvs)
                    axiom  = Role
-> Name
-> [Id]
-> [Id]
-> [Id]
-> TyCon
-> [Type]
-> Type
-> CoAxiom Unbranched
mkSingleCoAxiom Role
Representational Name
axiom_name
                                 [Id]
zonked_post_eta_qtvs [Id]
zonked_eta_tvs
                                 [] TyCon
fam_tc [Type]
eta_pats Type
ax_rhs
                    parent = CoAxiom Unbranched -> TyCon -> [Type] -> AlgTyConFlav
DataFamInstTyCon CoAxiom Unbranched
axiom TyCon
fam_tc [Type]
all_pats

                      -- NB: Use the full ty_binders from the pats. See bullet toward
                      -- the end of Note [Data type families] in GHC.Core.TyCon
                    rep_tc   = Name
-> [TyConBinder]
-> Type
-> [Role]
-> Maybe CType
-> [Type]
-> AlgTyConRhs
-> AlgTyConFlav
-> Bool
-> TyCon
mkAlgTyCon Name
rep_tc_name
                                          [TyConBinder]
ty_binders Type
res_kind
                                          ((TyConBinder -> Role) -> [TyConBinder] -> [Role]
forall a b. (a -> b) -> [a] -> [b]
map (Role -> TyConBinder -> Role
forall a b. a -> b -> a
const Role
Nominal) [TyConBinder]
ty_binders)
                                          ((GenLocated SrcSpanAnnP CType -> CType)
-> Maybe (GenLocated SrcSpanAnnP CType) -> Maybe CType
forall a b. (a -> b) -> Maybe a -> Maybe b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap GenLocated SrcSpanAnnP CType -> CType
forall l e. GenLocated l e -> e
unLoc Maybe (XRec GhcRn CType)
Maybe (GenLocated SrcSpanAnnP CType)
cType) [Type]
stupid_theta
                                          AlgTyConRhs
tc_rhs AlgTyConFlav
parent
                                          Bool
gadt_syntax
                 -- We always assume that indexed types are recursive.  Why?
                 -- (1) Due to their open nature, we can never be sure that a
                 -- further instance might not introduce a new recursive
                 -- dependency.  (2) They are always valid loop breakers as
                 -- they involve a coercion.

              ; return (rep_tc, (axiom, ax_rhs)) }

       -- Remember to check validity; no recursion to worry about here
       -- Check that left-hand sides are ok (mono-types, no type families,
       -- consistent instantiations, etc)
       ; let ax_branch = CoAxiom Unbranched -> KnotTied CoAxBranch
coAxiomSingleBranch CoAxiom Unbranched
axiom
       ; checkConsistentFamInst mb_clsinfo fam_tc ax_branch
       ; checkFamPatBinders fam_tc zonked_post_eta_qtvs non_user_tvs eta_pats ax_rhs
       ; checkValidCoAxBranch fam_tc ax_branch
       ; checkValidTyCon rep_tc

       ; let scoped_tvs = (Id -> (Name, Id)) -> [Id] -> [(Name, Id)]
forall a b. (a -> b) -> [a] -> [b]
map Id -> (Name, Id)
mk_deriv_info_scoped_tv_pr (TyCon -> [Id]
tyConTyVars TyCon
rep_tc)
             m_deriv_info = case HsDeriving GhcRn
derivs of
               []    -> Maybe DerivInfo
forall a. Maybe a
Nothing
               HsDeriving GhcRn
preds ->
                 DerivInfo -> Maybe DerivInfo
forall a. a -> Maybe a
Just (DerivInfo -> Maybe DerivInfo) -> DerivInfo -> Maybe DerivInfo
forall a b. (a -> b) -> a -> b
$ DerivInfo { di_rep_tc :: TyCon
di_rep_tc     = TyCon
rep_tc
                                  , di_scoped_tvs :: [(Name, Id)]
di_scoped_tvs = [(Name, Id)]
scoped_tvs
                                  , di_clauses :: HsDeriving GhcRn
di_clauses    = HsDeriving GhcRn
preds
                                  , di_ctxt :: ErrCtxtMsg
di_ctxt       = AssocInstInfo -> NewOrData -> DataFamInstDecl GhcRn -> ErrCtxtMsg
tcMkDataFamInstCtxt AssocInstInfo
mb_clsinfo NewOrData
new_or_data DataFamInstDecl GhcRn
decl
                                  }

       ; fam_inst <- newFamInst (DataFamilyInst rep_tc) axiom
       ; return (fam_inst, m_deriv_info) }
  where

    new_or_data :: NewOrData
new_or_data = DataDefnCons (GenLocated SrcSpanAnnA (ConDecl GhcRn)) -> NewOrData
forall a. DataDefnCons a -> NewOrData
dataDefnConsNewOrData DataDefnCons (LConDecl GhcRn)
DataDefnCons (GenLocated SrcSpanAnnA (ConDecl GhcRn))
hs_cons

    eta_reduce :: TyCon -> [Type] -> ([Type], [TyConBinder])
    -- See Note [Eta reduction for data families] in GHC.Core.Coercion.Axiom
    -- Splits the incoming patterns into two: the [TyVar]
    -- are the patterns that can be eta-reduced away.
    -- e.g.     T [a] Int a d c   ==>  (T [a] Int a, [d,c])
    --
    -- NB: quadratic algorithm, but types are small here
    eta_reduce :: TyCon -> [Type] -> ([Type], [TyConBinder])
eta_reduce TyCon
fam_tc [Type]
pats
        = [(Type, VarSet, TyConBndrVis)]
-> [TyConBinder] -> ([Type], [TyConBinder])
forall {c}.
[(Type, VarSet, c)] -> [VarBndr Id c] -> ([Type], [VarBndr Id c])
go ([(Type, VarSet, TyConBndrVis)] -> [(Type, VarSet, TyConBndrVis)]
forall a. [a] -> [a]
reverse ([Type]
-> [VarSet] -> [TyConBndrVis] -> [(Type, VarSet, TyConBndrVis)]
forall a b c. [a] -> [b] -> [c] -> [(a, b, c)]
zip3 [Type]
pats [VarSet]
fvs_s [TyConBndrVis]
vis_s)) []
        where
          vis_s :: [TyConBndrVis]
          vis_s :: [TyConBndrVis]
vis_s = TyCon -> [Type] -> [TyConBndrVis]
tcbVisibilities TyCon
fam_tc [Type]
pats

          fvs_s :: [TyCoVarSet]  -- 1-1 correspondence with pats
                                 -- Each elt is the free vars of all /earlier/ pats
          (VarSet
_, [VarSet]
fvs_s) = (VarSet -> Type -> (VarSet, VarSet))
-> VarSet -> [Type] -> (VarSet, [VarSet])
forall (t :: * -> *) s a b.
Traversable t =>
(s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL VarSet -> Type -> (VarSet, VarSet)
add_fvs VarSet
emptyVarSet [Type]
pats
          add_fvs :: VarSet -> Type -> (VarSet, VarSet)
add_fvs VarSet
fvs Type
pat = (VarSet
fvs VarSet -> VarSet -> VarSet
`unionVarSet` Type -> VarSet
tyCoVarsOfType Type
pat, VarSet
fvs)

    go :: [(Type, VarSet, c)] -> [VarBndr Id c] -> ([Type], [VarBndr Id c])
go ((Type
pat, VarSet
fvs_to_the_left, c
tcb_vis):[(Type, VarSet, c)]
pats) [VarBndr Id c]
etad_tvs
      | Just Id
tv <- Type -> Maybe Id
getTyVar_maybe Type
pat
      , Bool -> Bool
not (Id
tv Id -> VarSet -> Bool
`elemVarSet` VarSet
fvs_to_the_left)
      = [(Type, VarSet, c)] -> [VarBndr Id c] -> ([Type], [VarBndr Id c])
go [(Type, VarSet, c)]
pats (Id -> c -> VarBndr Id c
forall var argf. var -> argf -> VarBndr var argf
Bndr Id
tv c
tcb_vis VarBndr Id c -> [VarBndr Id c] -> [VarBndr Id c]
forall a. a -> [a] -> [a]
: [VarBndr Id c]
etad_tvs)
    go [(Type, VarSet, c)]
pats [VarBndr Id c]
etad_tvs = ([Type] -> [Type]
forall a. [a] -> [a]
reverse (((Type, VarSet, c) -> Type) -> [(Type, VarSet, c)] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map (Type, VarSet, c) -> Type
forall a b c. (a, b, c) -> a
fstOf3 [(Type, VarSet, c)]
pats), [VarBndr Id c]
etad_tvs)

    -- Create a Name-TyVar mapping to bring into scope when typechecking any
    -- deriving clauses this data family instance may have.
    -- See Note [Associated data family instances and di_scoped_tvs].
    mk_deriv_info_scoped_tv_pr :: TyVar -> (Name, TyVar)
    mk_deriv_info_scoped_tv_pr :: Id -> (Name, Id)
mk_deriv_info_scoped_tv_pr Id
tv =
      let n :: Name
n = TyVarEnv Name -> Name -> Id -> Name
forall a. VarEnv a -> a -> Id -> a
lookupWithDefaultVarEnv TyVarEnv Name
tv_skol_env (Id -> Name
tyVarName Id
tv) Id
tv
      in (Name
n, Id
tv)

{-
Note [Associated data family instances and di_scoped_tvs]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some care is required to implement `deriving` correctly for associated data
family instances. Consider this example from #18055:

  class C a where
    data D a

  class X a b

  instance C (Maybe a) where
    data D (Maybe a) deriving (X a)

When typechecking the `X a` in `deriving (X a)`, we must ensure that the `a`
from the instance header is brought into scope. This is the role of
di_scoped_tvs, which maps from the original, renamed `a` to the skolemized,
typechecked `a`. When typechecking the `deriving` clause, this mapping will be
consulted when looking up the `a` in `X a`.

A naïve attempt at creating the di_scoped_tvs is to simply reuse the
tyConTyVars of the representation TyCon for `data D (Maybe a)`. This is only
half correct, however. We do want the typechecked `a`'s Name in the /range/
of the mapping, but we do not want it in the /domain/ of the mapping.
To ensure that the original `a`'s Name ends up in the domain, we consult a
TyVarEnv (passed as an argument to tcDataFamInstDecl) that maps from the
typechecked `a`'s Name to the original `a`'s Name. In the even that
tcDataFamInstDecl is processing a non-associated data family instance, this
TyVarEnv will simply be empty, and there is nothing to worry about.
-}

-----------------------
tcDataFamInstHeader
    :: AssocInstInfo -> SkolemInfo -> TyCon -> HsOuterFamEqnTyVarBndrs GhcRn
    -> LexicalFixity -> Maybe (LHsContext GhcRn)
    -> HsFamEqnPats GhcRn -> Maybe (LHsKind GhcRn) -> DataDefnCons (LConDecl GhcRn)
    -> TcM ([TcTyVar], TyVarSet, [TcType], TcKind, TcThetaType)
         -- All skolem TcTyVars, all zonked so it's clear what the free vars are
-- The "header" of a data family instance is the part other than
-- the data constructors themselves
--    e.g.  data instance D [a] :: * -> * where ...
-- Here the "header" is the bit before the "where"
tcDataFamInstHeader :: AssocInstInfo
-> SkolemInfo
-> TyCon
-> HsOuterFamEqnTyVarBndrs GhcRn
-> LexicalFixity
-> Maybe (LHsContext GhcRn)
-> HsFamEqnPats GhcRn
-> Maybe (LHsKind GhcRn)
-> DataDefnCons (LConDecl GhcRn)
-> TcM ([Id], VarSet, [Type], Type, [Type])
tcDataFamInstHeader AssocInstInfo
mb_clsinfo SkolemInfo
skol_info TyCon
fam_tc HsOuterFamEqnTyVarBndrs GhcRn
hs_outer_bndrs LexicalFixity
fixity
                    Maybe (LHsContext GhcRn)
hs_ctxt HsFamEqnPats GhcRn
hs_pats Maybe (LHsKind GhcRn)
m_ksig DataDefnCons (LConDecl GhcRn)
hs_cons
  = do { String -> SDoc -> TcRn ()
traceTc String
"tcDataFamInstHeader {" (TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [HsArg
   GhcRn
   (GenLocated SrcSpanAnnA (HsType GhcRn))
   (GenLocated SrcSpanAnnA (HsType GhcRn))]
-> SDoc
forall a. Outputable a => a -> SDoc
ppr HsFamEqnPats GhcRn
[HsArg
   GhcRn
   (GenLocated SrcSpanAnnA (HsType GhcRn))
   (GenLocated SrcSpanAnnA (HsType GhcRn))]
hs_pats)
       ; (tclvl, wanted, (outer_bndrs, (stupid_theta, lhs_ty, master_res_kind, instance_res_kind)))
            <- String
-> TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))
-> TcM
     (TcLevel, WantedConstraints,
      (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type)))
forall a. String -> TcM a -> TcM (TcLevel, WantedConstraints, a)
pushLevelAndSolveEqualitiesX String
"tcDataFamInstHeader" (TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))
 -> TcM
      (TcLevel, WantedConstraints,
       (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))))
-> TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))
-> TcM
     (TcLevel, WantedConstraints,
      (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type)))
forall a b. (a -> b) -> a -> b
$
               SkolemInfo
-> HsOuterFamEqnTyVarBndrs GhcRn
-> TcM ([Type], Type, Type, Type)
-> TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))
forall a.
SkolemInfo
-> HsOuterFamEqnTyVarBndrs GhcRn
-> TcM a
-> TcM (HsOuterFamEqnTyVarBndrs GhcTc, a)
bindOuterFamEqnTKBndrs SkolemInfo
skol_info HsOuterFamEqnTyVarBndrs GhcRn
hs_outer_bndrs    (TcM ([Type], Type, Type, Type)
 -> TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type)))
-> TcM ([Type], Type, Type, Type)
-> TcM (HsOuterFamEqnTyVarBndrs GhcTc, ([Type], Type, Type, Type))
forall a b. (a -> b) -> a -> b
$  -- Binds skolem TcTyVars
               do { stupid_theta <- Maybe (LHsContext GhcRn) -> TcM [Type]
tcHsContext Maybe (LHsContext GhcRn)
hs_ctxt
                  ; (lhs_ty, lhs_kind) <- tcFamTyPats fam_tc hs_pats
                  ; (lhs_applied_ty, lhs_applied_kind)
                      <- tcInstInvisibleTyBinders lhs_ty lhs_kind
                      -- See Note [Data family/instance return kinds]
                      -- in GHC.Tc.TyCl point (DF3)

                  -- Ensure that the instance is consistent
                  -- with its parent class
                  ; addConsistencyConstraints mb_clsinfo lhs_ty

                  -- Add constraints from the data constructors
                  -- Fix #25611
                  -- See DESIGN CHOICE in Note [Kind inference for data family instances]
                  ; when is_H98_or_newtype $ kcConDecls lhs_applied_kind hs_cons

                  -- Check that the result kind of the TyCon applied to its args
                  -- is compatible with the explicit signature (or Type, if there
                  -- is none)
                  ; let hs_lhs = PromotionFlag
-> LexicalFixity
-> IdP GhcRn
-> HsFamEqnPats GhcRn
-> LHsKind GhcRn
forall (p :: Pass) a.
IsSrcSpanAnn p a =>
PromotionFlag
-> LexicalFixity
-> IdP (GhcPass p)
-> [LHsTypeArg (GhcPass p)]
-> LHsType (GhcPass p)
nlHsTyConApp PromotionFlag
NotPromoted LexicalFixity
fixity (TyCon -> Name
forall a. NamedThing a => a -> Name
getName TyCon
fam_tc) HsFamEqnPats GhcRn
hs_pats
                  -- Add constraints from the result signature
                  ; res_kind <- tc_kind_sig m_ksig
                  ; _ <- unifyKind (Just . HsTypeRnThing $ unLoc hs_lhs) lhs_applied_kind res_kind

                  ; traceTc "tcDataFamInstHeader" $
                    vcat [ ppr fam_tc, ppr m_ksig, ppr lhs_applied_kind, ppr res_kind, ppr m_ksig]
                  ; return ( stupid_theta
                           , lhs_applied_ty
                           , lhs_applied_kind
                           , res_kind ) }

       ; outer_bndrs <- scopedSortOuter outer_bndrs
       ; let outer_tvs = HsOuterFamEqnTyVarBndrs GhcTc -> [Id]
forall flag. HsOuterTyVarBndrs flag GhcTc -> [Id]
outerTyVars HsOuterFamEqnTyVarBndrs GhcTc
outer_bndrs
       ; checkFamTelescope tclvl hs_outer_bndrs outer_tvs

       -- This code (and the stuff immediately above) is very similar
       -- to that in tcTyFamInstEqnGuts.  Maybe we should abstract the
       -- common code; but for the moment I concluded that it's
       -- clearer to duplicate it.  Still, if you fix a bug here,
       -- check there too!

       -- See GHC.Tc.TyCl Note [Generalising in tcTyFamInstEqnGuts]
       ; dvs  <- candidateQTyVarsWithBinders outer_tvs lhs_ty
       ; qtvs <- quantifyTyVars skol_info TryNotToDefaultNonStandardTyVars dvs
       ; let final_tvs = [Id] -> [Id]
scopedSort ([Id]
qtvs [Id] -> [Id] -> [Id]
forall a. [a] -> [a] -> [a]
++ [Id]
outer_tvs)
             -- This scopedSort is important: the qtvs may be /interleaved/ with
             -- the outer_tvs.  See Note [Generalising in tcTyFamInstEqnGuts]
       ; reportUnsolvedEqualities skol_info final_tvs tclvl wanted

       ; (final_tvs, non_user_tvs, lhs_ty, master_res_kind, instance_res_kind, stupid_theta) <-
          liftZonkM $ do
            { final_tvs         <- mapM zonkTcTyVarToTcTyVar final_tvs
            ; non_user_tvs      <- mapM zonkTcTyVarToTcTyVar qtvs
            ; lhs_ty            <- zonkTcType                lhs_ty
            ; master_res_kind   <- zonkTcType                master_res_kind
            ; instance_res_kind <- zonkTcType                instance_res_kind
            ; stupid_theta      <- zonkTcTypes               stupid_theta
            ; return (final_tvs, non_user_tvs, lhs_ty, master_res_kind, instance_res_kind, stupid_theta) }

       -- Check that res_kind is OK with checkDataKindSig.  We need to
       -- check that it's ok because res_kind can come from a user-written
       -- kind signature.  See Note [Datatype return kinds], point (4a)
       ; checkDataKindSig (DataInstanceSort new_or_data) master_res_kind
       ; checkDataKindSig (DataInstanceSort new_or_data) instance_res_kind

       -- Split up the LHS type to get the type patterns
       -- For the scopedSort see Note [Generalising in tcTyFamInstEqnGuts]
       ; let pats      = Type -> [Type]
unravelFamInstPats Type
lhs_ty

       ; return (final_tvs, mkVarSet non_user_tvs, pats, master_res_kind, stupid_theta) }
  where
    fam_name :: Name
fam_name  = TyCon -> Name
tyConName TyCon
fam_tc
    data_ctxt :: UserTypeCtxt
data_ctxt = Name -> UserTypeCtxt
DataKindCtxt Name
fam_name
    new_or_data :: NewOrData
new_or_data = DataDefnCons (GenLocated SrcSpanAnnA (ConDecl GhcRn)) -> NewOrData
forall a. DataDefnCons a -> NewOrData
dataDefnConsNewOrData DataDefnCons (LConDecl GhcRn)
DataDefnCons (GenLocated SrcSpanAnnA (ConDecl GhcRn))
hs_cons
    is_H98_or_newtype :: Bool
is_H98_or_newtype = case DataDefnCons (LConDecl GhcRn)
hs_cons of
      NewTypeCon{} -> Bool
True
      DataTypeCons Bool
_ [LConDecl GhcRn]
cons -> (GenLocated SrcSpanAnnA (ConDecl GhcRn) -> Bool)
-> [GenLocated SrcSpanAnnA (ConDecl GhcRn)] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all GenLocated SrcSpanAnnA (ConDecl GhcRn) -> Bool
forall {l} {pass}. GenLocated l (ConDecl pass) -> Bool
isH98 [LConDecl GhcRn]
[GenLocated SrcSpanAnnA (ConDecl GhcRn)]
cons
    isH98 :: GenLocated l (ConDecl pass) -> Bool
isH98 (L l
_ (ConDeclH98 {})) = Bool
True
    isH98 GenLocated l (ConDecl pass)
_ = Bool
False

    -- See Note [Implementation of UnliftedNewtypes] in GHC.Tc.TyCl, families (2),
    -- Note [Implementation of UnliftedDatatypes]
    -- and Note [Defaulting result kind of newtype/data family instance].
    tc_kind_sig :: Maybe (GenLocated SrcSpanAnnA (HsType GhcRn)) -> TcM Type
tc_kind_sig Maybe (GenLocated SrcSpanAnnA (HsType GhcRn))
Nothing
      = do { unlifted_newtypes  <- Extension -> TcRn Bool
forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.UnliftedNewtypes
           ; unlifted_datatypes <- xoptM LangExt.UnliftedDatatypes
           ; case new_or_data of
               NewOrData
NewType  | Bool
unlifted_newtypes  -> TcM Type
newOpenTypeKind
               NewOrData
DataType | Bool
unlifted_datatypes -> TcM Type
newOpenTypeKind
               NewOrData
_                             -> Type -> TcM Type
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (f :: * -> *) a. Applicative f => a -> f a
pure Type
liftedTypeKind
           }

    -- See Note [Result kind signature for a data family instance]
    tc_kind_sig (Just GenLocated SrcSpanAnnA (HsType GhcRn)
hs_kind)
      = do { sig_kind <- UserTypeCtxt -> LHsKind GhcRn -> TcM Type
tcLHsKindSig UserTypeCtxt
data_ctxt LHsKind GhcRn
GenLocated SrcSpanAnnA (HsType GhcRn)
hs_kind
           ; (_tvs', inner_kind') <- tcSkolemiseInvisibleBndrs (SigTypeSkol data_ctxt) sig_kind
                   -- Perhaps surprisingly, we don't need the skolemised tvs themselves
           ; return inner_kind' }

{- Note [Result kind signature for a data family instance]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The expected type might have a forall at the type. Normally, we
can't skolemise in kinds because we don't have type-level lambda.
But here, we're at the top-level of an instance declaration, so
we actually have a place to put the regeneralised variables.
Thus: skolemise away. cf. GHC.Tc.Utils.Unify.tcTopSkolemise
Examples in indexed-types/should_compile/T12369

Note [Defaulting result kind of newtype/data family instance]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is tempting to let `tc_kind_sig` just return `newOpenTypeKind`
even without `-XUnliftedNewtypes`, but we rely on `tc_kind_sig` to
constrain the result kind of a newtype instance to `Type`.
Consider the following example:

  -- no UnliftedNewtypes
  data family D :: k -> k
  newtype instance D a = MkIntD a

`tc_kind_sig` defaulting to `newOpenTypeKind` would result in `D a`
having kind `forall r. TYPE r` instead of `Type`, which would be
rejected validity checking. The same applies to Data Instances.

Note [Implementing eta reduction for data families]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   data D :: * -> * -> * -> * -> *

   data instance D [(a,b)] p q :: * -> * where
      D1 :: blah1
      D2 :: blah2

Then we'll generate a representation data type
  data Drep a b p q z where
      D1 :: blah1
      D2 :: blah2

and an axiom to connect them
  axiom AxDrep forall a b p q z. D [(a,b]] p q z = Drep a b p q z

except that we'll eta-reduce the axiom to
  axiom AxDrep forall a b. D [(a,b]] = Drep a b

This is described at some length in Note [Eta reduction for data families]
in GHC.Core.Coercion.Axiom. There are several fiddly subtleties lurking here,
however, so this Note aims to describe these subtleties:

* The representation tycon Drep is parameterised over the free
  variables of the pattern, in no particular order. So there is no
  guarantee that 'p' and 'q' will come last in Drep's parameters, and
  in the right order.  So, if the /patterns/ of the family instance
  are eta-reducible, we re-order Drep's parameters to put the
  eta-reduced type variables last.

* Although we eta-reduce the axiom, we eta-/expand/ the representation
  tycon Drep.  The kind of D says it takes four arguments, but the
  data instance header only supplies three.  But the AlgTyCon for Drep
  itself must have enough TyConBinders so that its result kind is Type.
  So, with etaExpandAlgTyCon we make up some extra TyConBinders.
  See point (3) in Note [Datatype return kinds] in GHC.Tc.TyCl.

* The result kind in the instance might be a polykind, like this:
     data family DP a :: forall k. k -> *
     data instance DP [b] :: forall k1 k2. (k1,k2) -> *

  So in type-checking the LHS (DP Int) we need to check that it is
  more polymorphic than the signature.  To do that we must skolemise
  the signature and instantiate the call of DP.  So we end up with
     data instance DP [b] @(k1,k2) (z :: (k1,k2)) where

  Note that we must parameterise the representation tycon DPrep over
  'k1' and 'k2', as well as 'b'.

  The skolemise bit is done in tc_kind_sig, while the instantiate bit
  is done by tcFamTyPats.

* Very fiddly point.  When we eta-reduce to
     axiom AxDrep forall a b. D [(a,b]] = Drep a b

  we want the kind of (D [(a,b)]) to be the same as the kind of
  (Drep a b).  This ensures that applying the axiom doesn't change the
  kind.  Why is that hard?  Because the kind of (Drep a b) depends on
  the TyConBndrVis on Drep's arguments. In particular do we have
    (forall (k::*). blah) or (* -> blah)?

  We must match whatever D does!  In #15817 we had
      data family X a :: forall k. * -> *   -- Note: a forall that is not used
      data instance X Int b = MkX

  So the data instance is really
      data istance X Int @k b = MkX

  The axiom will look like
      axiom    X Int = Xrep

  and it's important that XRep :: forall k * -> *, following X.

  To achieve this we get the TyConBndrVis flags from tcbVisibilities,
  and use those flags for any eta-reduced arguments.  Sigh.

* The final turn of the knife is that tcbVisibilities is itself
  tricky to sort out.  Consider
      data family D k :: k
  Then consider D (forall k2. k2 -> k2) Type Type
  The visibility flags on an application of D may affected by the arguments
  themselves.  Heavy sigh.  But not truly hard; that's what tcbVisibilities
  does.

* Happily, we don't need to worry about the possibility of
  building an inhomogeneous axiom, described in GHC.Tc.TyCl.Build
  Note [Newtype eta and homogeneous axioms].   For example
     type F :: Type -> forall (b :: Type) -> Type
     data family F a b
     newtype instance F Int b = MkF (Proxy b)
  we get a newtype, and a eta-reduced axiom connecting the data family
  with the newtype:
     type R:FIntb :: forall (b :: Type) -> Type
     newtype R:FIntb b = MkF (Proxy b)
     axiom Foo.D:R:FIntb0 :: F Int = Foo.R:FIntb
  Now the subtleties of Note [Newtype eta and homogeneous axioms] are
  dealt with by the newtype (via mkNewTyConRhs called in tcDataFamInstDecl)
  while the axiom connecting F Int ~ R:FIntb is eta-reduced, but the
  quantifier 'b' is derived from the original data family F, and so the
  kinds will always match.

Note [Kind inference for data family instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this GADT-style data type declaration, where I have used
fresh variables in the data constructor's type, to stress that c,d are
quite distinct from a,b.
   data T a b where
     MkT :: forall c d. c d -> T c d

Following Note [Inferring kinds for type declarations] in GHC.Tc.TyCl,
to infer T's kind, we initially give T :: kappa, a monomorpic kind,
gather constraints from the header and data constructors, and conclude
   T :: (kappa1 -> type) -> kappa1 -> Type
Then we generalise, giving
   T :: forall k. (k->Type) -> k -> Type

Now what about a data /instance/ decl
   data family T :: forall k. (k->Type) -> k -> Type

   data instance T p Int where ...

No doubt here! The poly-kinded T is instantiated with k=Type, so the
header really looks like
   data instance T @Type (p :: Type->Type) Int where ...

But what about this?
   data instance T p q where
      MkT :: forall r. r Int -> T r Int

So what kind do 'p' and 'q' have?  No clues from the header, but from
the data constructor we can clearly see that (r :: Type->Type).  Does
that mean that the /entire data instance/ is instantiated at Type,
like this?
   data instance T @Type (p :: Type->Type) (q :: Type) where
      ...

Not at all! This is a /GADT/-style decl, so the kind argument might
be specialised in this particular data constructor, thus:
   data instance T @k (p :: k->Type) (q :: k) where
     MkT :: forall (r :: Type -> Type).
            r Int -> T @Type r Int
(and perhaps specialised differently in some other data
constructor MkT2).

The key difference in this case and 'data T' at the top of this Note
is that we have no known kind for 'data T'. We thus forbid different
specialisations of T in its constructors, in an attempt to avoid
inferring polymorphic recursion. In data family T, however, there is
no problem with polymorphic recursion: we already /fully know/ T's
kind -- that came from the family declaration, and is not influenced
by the data instances -- and hence we /can/ specialise T's kind
differently in different GADT data constructors.

SHORT SUMMARY: In a data instance decl, it's not clear whether kind
constraints arising from the data constructors should be considered
local to the (GADT) data /constructor/ or should apply to the entire
data instance.

DESIGN CHOICE: In a data/newtype family instance declaration:
* We take account of the data constructors (via `kcConDecls`) for:
  * Haskell-98 style data instance declarations
  * All newtype instance declarations
  For Haskell-98 style declarations, there is no GADT refinement. And for
  GADT-style newtype declarations, no GADT matching is allowed anyway,
  so it's just a syntactic difference from Haskell-98.

* We /ignore/ the data constructors for:
  * GADT-style data instance declarations
  Here, the instance kinds are influenced only by the header.

This choice is implemented by the guarded call to `kcConDecls` in
`tcDataFamInstHeader`.

Observations:
* With `UnliftedNewtypes` or `UnliftedDatatypes`, looking at the data
  constructors is necessary to infer the kind of the result type for
  certain cases. Otherwise, additional kind signatures are required.
  Consider the following example in #25611:

    data family Fix :: (k -> Type) -> k
    newtype instance Fix f = In { out :: f (Fix f) }

  If we are not looking at the data constructors:
  * Without `UnliftedNewtypes`, it is accepted since `Fix f` is defaulted
    to `Type`.
  * But with `UnliftedNewtypes`, `Fix f` is defaulted to `TYPE r` where
    `r` is not scoped over the data constructor. Then the header `Fix f :: TYPE r`
    will fail to kind unify with `f (Fix f) :: Type`.

  Hence, we need to look at the data constructor to infer `Fix f :: Type`
  for this newtype instance.

This DESIGN CHOICE strikes a balance between well-rounded kind inference
and implementation simplicity. See #25611, #18891, and !4419 for more
discussion of this issue.

Kind inference for data types (Xie et al) https://arxiv.org/abs/1911.06153
takes a slightly different approach.
-}


{- *********************************************************************
*                                                                      *
      Class instance declarations, pass 2
*                                                                      *
********************************************************************* -}

tcInstDecls2 :: [LTyClDecl GhcRn] -> [InstInfo GhcRn]
             -> TcM (LHsBinds GhcTc)
-- (a) From each class declaration,
--      generate any default-method bindings
-- (b) From each instance decl
--      generate the dfun binding

tcInstDecls2 :: [LTyClDecl GhcRn] -> [InstInfo GhcRn] -> TcM (LHsBinds GhcTc)
tcInstDecls2 [LTyClDecl GhcRn]
tycl_decls [InstInfo GhcRn]
inst_decls
  = do  { -- (a) Default methods from class decls
          let class_decls :: [GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
class_decls = (GenLocated SrcSpanAnnA (TyClDecl GhcRn) -> Bool)
-> [GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
-> [GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
forall a. (a -> Bool) -> [a] -> [a]
filter (TyClDecl GhcRn -> Bool
forall pass. TyClDecl pass -> Bool
isClassDecl (TyClDecl GhcRn -> Bool)
-> (GenLocated SrcSpanAnnA (TyClDecl GhcRn) -> TyClDecl GhcRn)
-> GenLocated SrcSpanAnnA (TyClDecl GhcRn)
-> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenLocated SrcSpanAnnA (TyClDecl GhcRn) -> TyClDecl GhcRn
forall l e. GenLocated l e -> e
unLoc) [LTyClDecl GhcRn]
[GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
tycl_decls
        ; dm_binds_s <- (GenLocated SrcSpanAnnA (TyClDecl GhcRn)
 -> IOEnv
      (Env TcGblEnv TcLclEnv)
      [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)])
-> [GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     [[GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM LTyClDecl GhcRn -> TcM (LHsBinds GhcTc)
GenLocated SrcSpanAnnA (TyClDecl GhcRn)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
tcClassDecl2 [GenLocated SrcSpanAnnA (TyClDecl GhcRn)]
class_decls
        ; let dm_binds = [[GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]]
-> [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]]
dm_binds_s

          -- (b) instance declarations
        ; let dm_ids = CollectFlag GhcTc -> LHsBinds GhcTc -> [IdP GhcTc]
forall p idR.
CollectPass p =>
CollectFlag p -> LHsBindsLR p idR -> [IdP p]
collectHsBindsBinders CollectFlag GhcTc
forall p. CollectFlag p
CollNoDictBinders LHsBinds GhcTc
[GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
dm_binds
              -- Add the default method Ids (again)
              -- (they were already added in GHC.Tc.TyCl.Utils.tcAddImplicits)
              -- See Note [Default methods in the type environment]
        ; inst_binds_s <- tcExtendGlobalValEnv dm_ids $
                          mapM tcInstDecl2 inst_decls

          -- Done
        ; return (dm_binds ++ concat inst_binds_s) }

{- Note [Default methods in the type environment]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The default method Ids are already in the type environment (see Note
[Default method Ids and Template Haskell] in TcTyDcls), BUT they
don't have their InlinePragmas yet.  Usually that would not matter,
because the simplifier propagates information from binding site to
use.  But, unusually, when compiling instance decls we *copy* the
INLINE pragma from the default method to the method for that
particular operation (see Note [INLINE and default methods] below).

So right here in tcInstDecls2 we must re-extend the type envt with
the default method Ids replete with their INLINE pragmas.  Urk.
-}

tcInstDecl2 :: InstInfo GhcRn -> TcM (LHsBinds GhcTc)
            -- Returns a binding for the dfun
tcInstDecl2 :: InstInfo GhcRn -> TcM (LHsBinds GhcTc)
tcInstDecl2 (InstInfo { iSpec :: forall a. InstInfo a -> ClsInst
iSpec = ClsInst
ispec, iBinds :: forall a. InstInfo a -> InstBindings a
iBinds = InstBindings GhcRn
ibinds })
  = TcM (LHsBinds GhcTc)
-> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall r. TcRn r -> TcRn r -> TcRn r
recoverM ([GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return LHsBinds GhcTc
[GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
forall (idL :: Pass) idR. LHsBindsLR (GhcPass idL) idR
emptyLHsBinds)    (TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc))
-> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall a b. (a -> b) -> a -> b
$
    SrcSpan -> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan SrcSpan
loc                     (TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc))
-> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall a b. (a -> b) -> a -> b
$
    ErrCtxtMsg -> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall a. ErrCtxtMsg -> TcM a -> TcM a
addErrCtxt (Type -> ErrCtxtMsg
instDeclCtxt2 Type
dfun_ty) (TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc))
-> TcM (LHsBinds GhcTc) -> TcM (LHsBinds GhcTc)
forall a b. (a -> b) -> a -> b
$
    do {  -- Instantiate the instance decl with skolem constants
         (skol_info, inst_tyvars, dfun_theta, clas, inst_tys) <- Type -> TcM (SkolemInfoAnon, [Id], [Type], Class, [Type])
tcSkolDFunType Type
dfun_ty
       ; dfun_ev_vars <- newEvVars dfun_theta

       ; let (class_tyvars, sc_theta, _, op_items) = classBigSig clas
             sc_theta' = HasDebugCallStack => Subst -> [Type] -> [Type]
Subst -> [Type] -> [Type]
substTheta ([Id] -> [Type] -> Subst
HasDebugCallStack => [Id] -> [Type] -> Subst
zipTvSubst [Id]
class_tyvars [Type]
inst_tys) [Type]
sc_theta

       ; traceTc "tcInstDecl2" (vcat [ppr inst_tyvars, ppr inst_tys, ppr dfun_theta, ppr sc_theta'])

                      -- Deal with 'SPECIALISE instance' pragmas
                      -- See Note [SPECIALISE instance pragmas]
       ; spec_inst_info@(spec_inst_prags,_) <- tcSpecInstPrags dfun_id ibinds

         -- Typecheck superclasses and methods
         -- See Note [Typechecking plan for instance declarations]
       ; dfun_ev_binds_var <- newTcEvBinds
       ; let dfun_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
dfun_ev_binds_var
       ; (tclvl, (sc_meth_ids, sc_meth_binds, sc_meth_implics))
             <- pushTcLevelM $
                do { (sc_ids, sc_binds, sc_implics)
                        <- tcSuperClasses skol_info dfun_id clas inst_tyvars
                                          dfun_ev_vars dfun_ev_binds sc_theta'

                      -- Typecheck the methods
                   ; (meth_ids, meth_binds, meth_implics)
                        <- tcMethods skol_info dfun_id clas inst_tyvars dfun_ev_vars
                                     inst_tys dfun_ev_binds spec_inst_info
                                     op_items ibinds

                   ; return ( sc_ids     ++          meth_ids
                            , sc_binds   ++ meth_binds
                            , sc_implics `unionBags` meth_implics ) }

       ; imp <- newImplication
       ; emitImplication $
         imp { ic_tclvl  = tclvl
             , ic_skols  = inst_tyvars
             , ic_given  = dfun_ev_vars
             , ic_wanted = mkImplicWC sc_meth_implics
             , ic_binds  = dfun_ev_binds_var
             , ic_info   = skol_info }

       -- Create the result bindings
       ; self_dict <- newDict clas inst_tys
       ; let class_tc      = Class -> TyCon
classTyCon Class
clas
             loc'          = SrcSpan -> SrcSpanAnnA
forall e. HasAnnotation e => SrcSpan -> e
noAnnSrcSpan SrcSpan
loc
             dict_constr   = TyCon -> DataCon
tyConSingleDataCon TyCon
class_tc
             dict_bind = IdP GhcTc -> LHsExpr GhcTc -> LHsBind GhcTc
mkVarBind IdP GhcTc
Id
self_dict (SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' HsExpr GhcTc
con_app_args)

                     -- We don't produce a binding for the dict_constr; instead we
                     -- rely on the simplifier to unfold this saturated application
                     -- We do this rather than generate an HsCon directly, because
                     -- it means that the special cases (e.g. dictionary with only one
                     -- member) are dealt with by the common MkId.mkDataConWrapId
                     -- code rather than needing to be repeated here.
                     --    con_app_tys  = MkD ty1 ty2
                     --    con_app_scs  = MkD ty1 ty2 sc1 sc2
                     --    con_app_args = MkD ty1 ty2 sc1 sc2 op1 op2
             con_app_tys  = HsWrapper -> HsExpr GhcTc -> HsExpr GhcTc
mkHsWrap ([Type] -> HsWrapper
mkWpTyApps [Type]
inst_tys) (HsExpr GhcTc -> HsExpr GhcTc) -> HsExpr GhcTc -> HsExpr GhcTc
forall a b. (a -> b) -> a -> b
$
                            ConLike -> HsExpr GhcTc
mkConLikeTc (DataCon -> ConLike
RealDataCon DataCon
dict_constr)
                       -- NB: We *can* have covars in inst_tys, in the case of
                       -- promoted GADT constructors.

             con_app_args = (HsExpr GhcTc -> Id -> HsExpr GhcTc)
-> HsExpr GhcTc -> [Id] -> HsExpr GhcTc
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' HsExpr GhcTc -> Id -> HsExpr GhcTc
app_to_meth HsExpr GhcTc
con_app_tys [Id]
sc_meth_ids

             app_to_meth :: HsExpr GhcTc -> Id -> HsExpr GhcTc
             app_to_meth HsExpr GhcTc
fun Id
meth_id = XApp GhcTc -> LHsExpr GhcTc -> LHsExpr GhcTc -> HsExpr GhcTc
forall p. XApp p -> LHsExpr p -> LHsExpr p -> HsExpr p
HsApp XApp GhcTc
NoExtField
noExtField (SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' HsExpr GhcTc
fun)
                                            (SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' (HsWrapper -> Id -> HsExpr GhcTc
wrapId HsWrapper
arg_wrapper Id
meth_id))

             inst_tv_tys = [Id] -> [Type]
mkTyVarTys [Id]
inst_tyvars
             arg_wrapper = [Id] -> HsWrapper
mkWpEvVarApps [Id]
dfun_ev_vars HsWrapper -> HsWrapper -> HsWrapper
<.> [Type] -> HsWrapper
mkWpTyApps [Type]
inst_tv_tys

             is_newtype = TyCon -> Bool
isNewTyCon TyCon
class_tc
             dfun_id_w_prags = Id -> [Id] -> Id
addDFunPrags Id
dfun_id [Id]
sc_meth_ids
             dfun_spec_prags
                | Bool
is_newtype = [LTcSpecPrag] -> TcSpecPrags
SpecPrags []
                | Bool
otherwise  = [LTcSpecPrag] -> TcSpecPrags
SpecPrags [LTcSpecPrag]
spec_inst_prags
                    -- Newtype dfuns just inline unconditionally,
                    -- so don't attempt to specialise them

             export = ABE { abe_wrap :: HsWrapper
abe_wrap = HsWrapper
idHsWrapper
                          , abe_poly :: Id
abe_poly = Id
dfun_id_w_prags
                          , abe_mono :: Id
abe_mono = Id
self_dict
                          , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
dfun_spec_prags }
                          -- NB: see Note [SPECIALISE instance pragmas]
             main_bind = XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall idL idR. XXHsBindsLR idL idR -> HsBindLR idL idR
XHsBindsLR (XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc)
-> XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall a b. (a -> b) -> a -> b
$
                         AbsBinds { abs_tvs :: [Id]
abs_tvs = [Id]
inst_tyvars
                                  , abs_ev_vars :: [Id]
abs_ev_vars = [Id]
dfun_ev_vars
                                  , abs_exports :: [ABExport]
abs_exports = [ABExport
export]
                                  , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = []
                                  , abs_binds :: LHsBinds GhcTc
abs_binds = [LHsBind GhcTc
dict_bind]
                                  , abs_sig :: Bool
abs_sig = Bool
True }

       ; return (L loc' main_bind : sc_meth_binds)
       }
 where
   dfun_id :: Id
dfun_id = ClsInst -> Id
instanceDFunId ClsInst
ispec
   dfun_ty :: Type
dfun_ty = Id -> Type
idType Id
dfun_id
   loc :: SrcSpan
loc     = Id -> SrcSpan
forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id

addDFunPrags :: DFunId -> [Id] -> DFunId
-- DFuns need a special Unfolding and InlinePrag
--    See Note [ClassOp/DFun selection]
--    and Note [Single-method classes]
-- It's easiest to create those unfoldings right here, where
-- have all the pieces in hand, even though we are messing with
-- Core at this point, which the typechecker doesn't usually do
-- However we take care to build the unfolding using the TyVars from
-- the DFunId rather than from the skolem pieces that the typechecker
-- is messing with.
addDFunPrags :: Id -> [Id] -> Id
addDFunPrags Id
dfun_id [Id]
sc_meth_ids
 | Bool
is_newtype
  = Id
dfun_id Id -> Unfolding -> Id
`setIdUnfolding`  SimpleOpts -> UnfoldingSource -> Int -> CoreExpr -> Unfolding
mkInlineUnfoldingWithArity SimpleOpts
defaultSimpleOpts UnfoldingSource
StableSystemSrc Int
0 CoreExpr
con_app
            Id -> InlinePragma -> Id
`setInlinePragma` InlinePragma
alwaysInlinePragma { inl_sat = Just 0 }
 | Bool
otherwise
 = Id
dfun_id Id -> Unfolding -> Id
`setIdUnfolding`  [Id] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding [Id]
dfun_bndrs DataCon
dict_con [CoreExpr]
dict_args
           Id -> InlinePragma -> Id
`setInlinePragma` InlinePragma
dfunInlinePragma
 where
   con_app :: CoreExpr
con_app    = [Id] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams [Id]
dfun_bndrs (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
                CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
mkApps (Id -> CoreExpr
forall b. Id -> Expr b
Var (DataCon -> Id
dataConWrapId DataCon
dict_con)) [CoreExpr]
dict_args
                -- This application will satisfy the Core invariants
                -- from Note [Representation polymorphism invariants] in GHC.Core,
                -- because typeclass method types are never unlifted.
   dict_args :: [CoreExpr]
dict_args  = (Type -> CoreExpr) -> [Type] -> [CoreExpr]
forall a b. (a -> b) -> [a] -> [b]
map Type -> CoreExpr
forall b. Type -> Expr b
Type [Type]
inst_tys [CoreExpr] -> [CoreExpr] -> [CoreExpr]
forall a. [a] -> [a] -> [a]
++
                [CoreExpr -> [Id] -> CoreExpr
forall b. Expr b -> [Id] -> Expr b
mkVarApps (Id -> CoreExpr
forall b. Id -> Expr b
Var Id
id) [Id]
dfun_bndrs | Id
id <- [Id]
sc_meth_ids]

   ([Id]
dfun_tvs, [Type]
dfun_theta, Class
clas, [Type]
inst_tys) = Type -> ([Id], [Type], Class, [Type])
tcSplitDFunTy (Id -> Type
idType Id
dfun_id)
   ev_ids :: [Id]
ev_ids      = Int -> [Type] -> [Id]
mkTemplateLocalsNum Int
1                    [Type]
dfun_theta
   dfun_bndrs :: [Id]
dfun_bndrs  = [Id]
dfun_tvs [Id] -> [Id] -> [Id]
forall a. [a] -> [a] -> [a]
++ [Id]
ev_ids
   clas_tc :: TyCon
clas_tc     = Class -> TyCon
classTyCon Class
clas
   dict_con :: DataCon
dict_con    = TyCon -> DataCon
tyConSingleDataCon TyCon
clas_tc
   is_newtype :: Bool
is_newtype  = TyCon -> Bool
isNewTyCon TyCon
clas_tc

wrapId :: HsWrapper -> Id -> HsExpr GhcTc
wrapId :: HsWrapper -> Id -> HsExpr GhcTc
wrapId HsWrapper
wrapper Id
id = HsWrapper -> HsExpr GhcTc -> HsExpr GhcTc
mkHsWrap HsWrapper
wrapper (XVar GhcTc -> LIdP GhcTc -> HsExpr GhcTc
forall p. XVar p -> LIdP p -> HsExpr p
HsVar XVar GhcTc
NoExtField
noExtField (Id -> GenLocated SrcSpanAnnN Id
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA Id
id))

{- Note [Typechecking plan for instance declarations]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For instance declarations we generate the following bindings and implication
constraints.  Example:

   instance Ord a => Ord [a] where compare = <compare-rhs>

generates this:

   Bindings:
      -- Method bindings
      $ccompare :: forall a. Ord a => a -> a -> Ordering
      $ccompare = /\a \(d:Ord a). let <meth-ev-binds> in ...

      -- Superclass bindings
      $cp1Ord :: forall a. Ord a => Eq [a]
      $cp1Ord = /\a \(d:Ord a). let <sc-ev-binds>
               in dfEqList (dw :: Eq a)

   Constraints:
      forall a. Ord a =>
                -- Method constraint
             (forall. (empty) => <constraints from compare-rhs>)
                -- Superclass constraint
          /\ (forall. (empty) => dw :: Eq a)

Notice that

 * Per-meth/sc implication.  There is one inner implication per
   superclass or method, with no skolem variables or givens.  The only
   reason for this one is to gather the evidence bindings privately
   for this superclass or method.  This implication is generated
   by checkInstConstraints.

 * Overall instance implication. There is an overall enclosing
   implication for the whole instance declaration, with the expected
   skolems and givens.  We need this to get the correct "redundant
   constraint" warnings, gathering all the uses from all the methods
   and superclasses.  See GHC.Tc.Solver Note [Tracking redundant
   constraints]

 * The given constraints in the outer implication may generate
   evidence, notably by superclass selection.  Since the method and
   superclass bindings are top-level, we want that evidence copied
   into *every* method or superclass definition.  (Some of it will
   be usused in some, but dead-code elimination will drop it.)

   We achieve this by putting the evidence variable for the overall
   instance implication into the AbsBinds for each method/superclass.
   Hence the 'dfun_ev_binds' passed into tcMethods and tcSuperClasses.
   (And that in turn is why the abs_ev_binds field of AbBinds is a
   [TcEvBinds] rather than simply TcEvBinds.

   This is a bit of a hack, but works very nicely in practice.

 * Note that if a method has a locally-polymorphic binding, there will
   be yet another implication for that, generated by tcPolyCheck
   in tcMethodBody. E.g.
          class C a where
            foo :: forall b. Ord b => blah


************************************************************************
*                                                                      *
      Type-checking superclasses
*                                                                      *
************************************************************************
-}

tcSuperClasses :: SkolemInfoAnon -> DFunId -> Class -> [TcTyVar]
               -> [EvVar]
               -> TcEvBinds
               -> TcThetaType
               -> TcM ([EvVar], LHsBinds GhcTc, Bag Implication)
-- Make a new top-level function binding for each superclass,
-- something like
--    $Ordp1 :: forall a. Ord a => Eq [a]
--    $Ordp1 = /\a \(d:Ord a). dfunEqList a (sc_sel d)
--
-- See Note [Recursive superclasses] for why this is so hard!
-- In effect, we build a special-purpose solver for the first step
-- of solving each superclass constraint
tcSuperClasses :: SkolemInfoAnon
-> Id
-> Class
-> [Id]
-> [Id]
-> TcEvBinds
-> [Type]
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcSuperClasses SkolemInfoAnon
skol_info Id
dfun_id Class
cls [Id]
tyvars [Id]
dfun_evs TcEvBinds
dfun_ev_binds [Type]
sc_theta
  = do { (ids, binds, implics) <- ((Type, Int)
 -> IOEnv
      (Env TcGblEnv TcLclEnv)
      (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc), Implication))
-> [(Type, Int)]
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Implication])
forall (m :: * -> *) a b c d.
Monad m =>
(a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])
mapAndUnzip3M (Type, Int)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc), Implication)
tc_super ([Type] -> [Int] -> [(Type, Int)]
forall a b. [a] -> [b] -> [(a, b)]
zip [Type]
sc_theta [Int
fIRST_TAG..])
       ; return (ids, binds, listToBag implics) }
  where
    loc :: SrcSpan
loc = Id -> SrcSpan
forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id
    tc_super :: (Type, Int)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc), Implication)
tc_super (Type
sc_pred, Int
n)
      = do { (sc_implic, ev_binds_var, sc_ev_tm)
                <- SkolemInfoAnon
-> TcM EvTerm -> TcM (Implication, EvBindsVar, EvTerm)
forall result.
SkolemInfoAnon
-> TcM result -> TcM (Implication, EvBindsVar, result)
checkInstConstraints SkolemInfoAnon
skol_info (TcM EvTerm -> TcM (Implication, EvBindsVar, EvTerm))
-> TcM EvTerm -> TcM (Implication, EvBindsVar, EvTerm)
forall a b. (a -> b) -> a -> b
$
                   CtOrigin -> Type -> TcM EvTerm
emitWanted (ClsInstOrQC -> NakedScFlag -> CtOrigin
ScOrigin ClsInstOrQC
IsClsInst NakedScFlag
NakedSc) Type
sc_pred
                   -- ScOrigin IsClsInst True: see Note [Solving superclass constraints]

           ; sc_top_name  <- newName (mkSuperDictAuxOcc n (getOccName cls))
           ; sc_ev_id     <- newEvVar sc_pred
           ; addTcEvBind ev_binds_var $ mkWantedEvBind sc_ev_id EvCanonical sc_ev_tm
           ; let sc_top_ty = [Id] -> [Type] -> Type -> Type
tcMkDFunSigmaTy [Id]
tyvars ((Id -> Type) -> [Id] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map Id -> Type
idType [Id]
dfun_evs) Type
sc_pred
                 sc_top_id = HasDebugCallStack => Name -> Type -> Type -> Id
Name -> Type -> Type -> Id
mkLocalId Name
sc_top_name Type
ManyTy Type
sc_top_ty
                 export = ABE { abe_wrap :: HsWrapper
abe_wrap = HsWrapper
idHsWrapper
                              , abe_poly :: Id
abe_poly = Id
sc_top_id
                              , abe_mono :: Id
abe_mono = Id
sc_ev_id
                              , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
noSpecPrags }
                 local_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
ev_binds_var
                 bind = XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall idL idR. XXHsBindsLR idL idR -> HsBindLR idL idR
XHsBindsLR (XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc)
-> XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall a b. (a -> b) -> a -> b
$
                        AbsBinds { abs_tvs :: [Id]
abs_tvs      = [Id]
tyvars
                                 , abs_ev_vars :: [Id]
abs_ev_vars  = [Id]
dfun_evs
                                 , abs_exports :: [ABExport]
abs_exports  = [ABExport
export]
                                 , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = [TcEvBinds
dfun_ev_binds, TcEvBinds
local_ev_binds]
                                 , abs_binds :: LHsBinds GhcTc
abs_binds    = []
                                 , abs_sig :: Bool
abs_sig      = Bool
False }
           ; return (sc_top_id, L (noAnnSrcSpan loc) bind, sc_implic) }

-------------------
checkInstConstraints :: SkolemInfoAnon -> TcM result
                     -> TcM (Implication, EvBindsVar, result)
-- See Note [Typechecking plan for instance declarations]
checkInstConstraints :: forall result.
SkolemInfoAnon
-> TcM result -> TcM (Implication, EvBindsVar, result)
checkInstConstraints SkolemInfoAnon
skol_info TcM result
thing_inside
  = do { (tclvl, wanted, result) <- TcM result -> TcM (TcLevel, WantedConstraints, result)
forall a. TcM a -> TcM (TcLevel, WantedConstraints, a)
pushLevelAndCaptureConstraints  (TcM result -> TcM (TcLevel, WantedConstraints, result))
-> TcM result -> TcM (TcLevel, WantedConstraints, result)
forall a b. (a -> b) -> a -> b
$
                                    TcM result
thing_inside

       ; ev_binds_var <- newTcEvBinds
       ; implic <- newImplication
       ; let implic' = Implication
implic { ic_tclvl  = tclvl
                              , ic_wanted = wanted
                              , ic_binds  = ev_binds_var
                              , ic_info   = skol_info }

       ; return (implic', ev_binds_var, result) }

{-
Note [Recursive superclasses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See #3731, #4809, #5751, #5913, #6117, #6161, which all
describe somewhat more complicated situations, but ones
encountered in practice.

See also tests tcrun020, tcrun021, tcrun033, and #11427.

----- THE PROBLEM --------
The problem is that it is all too easy to create a class whose
superclass is bottom when it should not be.

Consider the following (extreme) situation:
        class C a => D a where ...
        instance D [a] => D [a] where ...   (dfunD)
        instance C [a] => C [a] where ...   (dfunC)
Although this looks wrong (assume D [a] to prove D [a]), it is only a
more extreme case of what happens with recursive dictionaries, and it
can, just about, make sense because the methods do some work before
recursing.

To implement the dfunD we must generate code for the superclass C [a],
which we had better not get by superclass selection from the supplied
argument:
       dfunD :: forall a. D [a] -> D [a]
       dfunD = \d::D [a] -> MkD (scsel d) ..

Otherwise if we later encounter a situation where
we have a [Wanted] dw::D [a] we might solve it thus:
     dw := dfunD dw
Which is all fine except that now ** the superclass C is bottom **!

The instance we want is:
       dfunD :: forall a. D [a] -> D [a]
       dfunD = \d::D [a] -> MkD (dfunC (scsel d)) ...

----- THE SOLUTION --------
The basic solution is simple: be very careful about using superclass
selection to generate a superclass witness in a dictionary function
definition.  More precisely:

  Superclass Invariant: in every class dictionary,
                        every superclass dictionary field
                        is non-bottom

To achieve the Superclass Invariant, in a dfun definition we can
generate a guaranteed-non-bottom superclass witness from:
  (sc1) one of the dictionary arguments itself (all non-bottom)
  (sc2) an immediate superclass of a non-bottom dictionary that is
        /Paterson-smaller/ than the instance head
        See Note [The PatersonSize of a type] in GHC.Tc.Utils.TcType
  (sc3) a call of a dfun (always returns a dictionary constructor)

The tricky case is (sc2).  We proceed by induction on the size of the
(type of) the dictionary, defined by GHC.Tc.Utils.TcType.pSizeType.  Let's
suppose we are building a dictionary of size 3 (the "head"), and suppose
the Superclass Invariant holds of smaller dictionaries.  Then if we have a
smaller dictionary, its immediate superclasses will be non-bottom by
induction.

Why "Paterson-smaller"? See Note [Paterson conditions] in GHC.Tc.Validity.
We want to be sure that the superclass dictionary is smaller /for any
ground instatiation/ of the instance, so we need to account for type
variables that occur more than once, and for type families (#20666).  And
that's exactly what the Paterson conditions check!

Here is an example, taken from CmmExpr:
       class Ord r => UserOfRegs r a where ...
(i1)   instance UserOfRegs r a => UserOfRegs r (Maybe a) where
(i2)   instance (Ord r, UserOfRegs r CmmReg) => UserOfRegs r CmmExpr where

For (i1) we can get the (Ord r) superclass by selection from
(UserOfRegs r a), since it (i.e. UserOfRegs r a) is smaller than the
thing we are building, namely (UserOfRegs r (Maybe a)).

But for (i2) that isn't the case: (UserOfRegs r CmmReg) is not smaller
than the thing we are building (UserOfRegs r CmmExpr), so we can't use
the superclasses of the former.  Hence we must instead add an explicit,
and perhaps surprising, (Ord r) argument to the instance declaration.

Here's another example from #6161:

       class         Super a => Duper a  where ...
       class Duper (Maybe a) => Foo a    where ...
(i3)   instance Foo a => Duper (Maybe a) where ...
(i4)   instance                Foo Float where ...

It would be horribly wrong to define
   dfDuperMaybe :: Foo a -> Duper (Maybe a)  -- from (i3)
   dfDuperMaybe d = MkDuper (sc_sel1 (sc_sel2 d)) ...

   dfFooFloat :: Foo Float               -- from (i4)
   dfFooFloat = MkFoo (dfDuperMaybe dfFooFloat) ...

Let's expand the RHS of dfFooFloat:
   dfFooFloat = MkFoo (MkDuper (sc_sel1 (sc_sel2 dfFooFloat)) ...) ...
That superclass argument to MkDuper is bottom!

This program gets rejected because:
* When processing (i3) we need to construct a dictionary for Super
  (Maybe a), to put in the superclass field of (Duper (Maybe a)).
* We /can/ use the superclasses of (Foo a), because the latter is
  smaller than the head of the instance, namely Duper (Maybe a).
* So we know (by (sc2)) that this Duper (Maybe a) dictionary is
  non-bottom.  But because (Duper (Maybe a)) is not smaller than the
  instance head (Duper (Maybe a)), we can't take *its* superclasses.
As a result the program is rightly rejected, unless you add
(Super (Maybe a)) to the context of (i3).

Wrinkle (W1):
    (sc2) says we only get a non-bottom dict if the dict we are
    selecting from is itself non-bottom.  So in a superclass chain,
    all the dictionaries in the chain must be non-bottom.
        class C a => D3 a
        class D2 a [[Maybe b]] => D1 a b
        class D3 a             => D2 a b
        class C a => E a b
        instance D1 a b => E a [b]
    The instance needs the wanted superclass (C a).  We can get it
    by superclass selection from
       D1 a b --> D2 a [[Maybe b]] --> D3 a --> C a
    But on the way we go through the too-big (D2 a [[Maybe b]]), and
    we don't know that is non-bottom.

Note [Solving superclass constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
How do we ensure that every superclass witness in an instance declaration
is generated by one of (sc1) (sc2) or (sc3) in Note [Recursive superclasses]?
Answer:

  * The "given" constraints of an instance decl have CtOrigin of
    (GivenOrigin (InstSkol head_size)), where head_size is the
    PatersonSize of the head of the instance declaration.  E.g. in
        instance D a => C [a]
    the `[G] D a` constraint has a CtOrigin whose head_size is the
    PatersonSize of (C [a]).

  * When we make a superclass selection from a Given (transitively)
    we give it a CtOrigin of (GivenSCOrigin skol_info sc_depth blocked).

    The 'blocked :: Bool' flag says if the superclass can be used to
    solve a superclass Wanted. The new superclass is blocked unless:

       it is the superclass of an unblocked dictionary (wrinkle (W1)),
       that is Paterson-smaller than the instance head.

    This is implemented in GHC.Tc.Solver.Dict.mk_strict_superclasses
    (in the mk_given_loc helper function).

  * Superclass "Wanted" constraints have CtOrigin of (ScOrigin NakedSc)
    The 'NakedSc' says that this is a naked superclass Wanted; we must
    be careful when solving it.

  * (sc1) When we rewrite such a wanted constraint, it retains its
    origin.  But if we apply an instance declaration, we can set the
    origin to (ScOrigin NotNakedSc), thus lifting any restrictions by
    making prohibitedSuperClassSolve return False. This happens
    in GHC.Tc.Solver.Dict.checkInstanceOK.

  * (sc2) ScOrigin wanted constraints can't be solved from a
    superclass selection, except at a smaller type.  This test is
    implemented by GHC.Tc.Solver.InertSet.prohibitedSuperClassSolve

Note [Silent superclass arguments] (historical interest only)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NB1: this note describes our *old* solution to the
     recursive-superclass problem. I'm keeping the Note
     for now, just as institutional memory.
     However, the code for silent superclass arguments
     was removed in late Dec 2014

NB2: the silent-superclass solution introduced new problems
     of its own, in the form of instance overlap.  Tests
     SilentParametersOverlapping, T5051, and T7862 are examples

NB3: the silent-superclass solution also generated tons of
     extra dictionaries.  For example, in monad-transformer
     code, when constructing a Monad dictionary you had to pass
     an Applicative dictionary; and to construct that you need
     a Functor dictionary. Yet these extra dictionaries were
     often never used.  Test T3064 compiled *far* faster after
     silent superclasses were eliminated.

Our solution to this problem "silent superclass arguments".  We pass
to each dfun some ``silent superclass arguments’’, which are the
immediate superclasses of the dictionary we are trying to
construct. In our example:
       dfun :: forall a. C [a] -> D [a] -> D [a]
       dfun = \(dc::C [a]) (dd::D [a]) -> DOrd dc ...
Notice the extra (dc :: C [a]) argument compared to the previous version.

This gives us:

     -----------------------------------------------------------
     DFun Superclass Invariant
     ~~~~~~~~~~~~~~~~~~~~~~~~
     In the body of a DFun, every superclass argument to the
     returned dictionary is
       either   * one of the arguments of the DFun,
       or       * constant, bound at top level
     -----------------------------------------------------------

This net effect is that it is safe to treat a dfun application as
wrapping a dictionary constructor around its arguments (in particular,
a dfun never picks superclasses from the arguments under the
dictionary constructor). No superclass is hidden inside a dfun
application.

The extra arguments required to satisfy the DFun Superclass Invariant
always come first, and are called the "silent" arguments.  You can
find out how many silent arguments there are using Id.dfunNSilent;
and then you can just drop that number of arguments to see the ones
that were in the original instance declaration.

DFun types are built (only) by MkId.mkDictFunId, so that is where we
decide what silent arguments are to be added.
-}

{-
************************************************************************
*                                                                      *
      Type-checking an instance method
*                                                                      *
************************************************************************

tcMethod
- Make the method bindings, as a [(NonRec, HsBinds)], one per method
- Remembering to use fresh Name (the instance method Name) as the binder
- Bring the instance method Ids into scope, for the benefit of tcInstSig
- Use sig_fn mapping instance method Name -> instance tyvars
- Ditto prag_fn
- Use tcValBinds to do the checking
-}

tcMethods :: SkolemInfoAnon -> DFunId -> Class
          -> [TcTyVar] -> [EvVar]
          -> [TcType]
          -> TcEvBinds
          -> ([LTcSpecPrag], TcPragEnv)
          -> [ClassOpItem]
          -> InstBindings GhcRn
          -> TcM ([Id], LHsBinds GhcTc, Bag Implication)
        -- The returned inst_meth_ids all have types starting
        --      forall tvs. theta => ...
tcMethods :: SkolemInfoAnon
-> Id
-> Class
-> [Id]
-> [Id]
-> [Type]
-> TcEvBinds
-> ([LTcSpecPrag], TcPragEnv)
-> [ClassOpItem]
-> InstBindings GhcRn
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcMethods SkolemInfoAnon
skol_info Id
dfun_id Class
clas [Id]
tyvars [Id]
dfun_ev_vars [Type]
inst_tys
                  TcEvBinds
dfun_ev_binds ([LTcSpecPrag]
spec_inst_prags, TcPragEnv
prag_fn) [ClassOpItem]
op_items
                  (InstBindings { ib_binds :: forall a. InstBindings a -> LHsBinds a
ib_binds      = LHsBinds GhcRn
binds
                                , ib_tyvars :: forall a. InstBindings a -> [Name]
ib_tyvars     = [Name]
lexical_tvs
                                , ib_pragmas :: forall a. InstBindings a -> [LSig a]
ib_pragmas    = [LSig GhcRn]
sigs
                                , ib_extensions :: forall a. InstBindings a -> [Extension]
ib_extensions = [Extension]
exts
                                , ib_derived :: forall a. InstBindings a -> Bool
ib_derived    = Bool
is_derived })
  = [(Name, Id)]
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
forall r. [(Name, Id)] -> TcM r -> TcM r
tcExtendNameTyVarEnv ([Name]
lexical_tvs [Name] -> [Id] -> [(Name, Id)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Id]
tyvars) (TcM ([Id], LHsBinds GhcTc, Bag Implication)
 -> TcM ([Id], LHsBinds GhcTc, Bag Implication))
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
forall a b. (a -> b) -> a -> b
$
       -- The lexical_tvs scope over the 'where' part
    do { String -> SDoc -> TcRn ()
traceTc String
"tcInstMeth" ([GenLocated SrcSpanAnnA (Sig GhcRn)] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [LSig GhcRn]
[GenLocated SrcSpanAnnA (Sig GhcRn)]
sigs SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [GenLocated SrcSpanAnnA (HsBind GhcRn)] -> SDoc
forall a. Outputable a => a -> SDoc
ppr LHsBinds GhcRn
[GenLocated SrcSpanAnnA (HsBind GhcRn)]
binds)
       ; TcRn ()
checkMinimalDefinition
       ; TcRn ()
checkMethBindMembership
       ; (ids, binds, mb_implics) <- [Extension]
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
forall a. [Extension] -> TcM a -> TcM a
set_exts [Extension]
exts (TcM
   ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
    [Maybe Implication])
 -> TcM
      ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
       [Maybe Implication]))
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
forall a b. (a -> b) -> a -> b
$
                                     TcM
  ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
   [Maybe Implication])
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
forall a. TcM a -> TcM a
unset_warnings_deriving (TcM
   ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
    [Maybe Implication])
 -> TcM
      ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
       [Maybe Implication]))
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
forall a b. (a -> b) -> a -> b
$
                                     (ClassOpItem
 -> IOEnv
      (Env TcGblEnv TcLclEnv)
      (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
       Maybe Implication))
-> [ClassOpItem]
-> TcM
     ([Id], [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)],
      [Maybe Implication])
forall (m :: * -> *) a b c d.
Monad m =>
(a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])
mapAndUnzip3M ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
ClassOpItem
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
      Maybe Implication)
tc_item [ClassOpItem]
op_items
       ; return (ids, binds, listToBag (catMaybes mb_implics)) }
  where
    set_exts :: [LangExt.Extension] -> TcM a -> TcM a
    set_exts :: forall a. [Extension] -> TcM a -> TcM a
set_exts [Extension]
es TcM a
thing = (Extension -> TcM a -> TcM a) -> TcM a -> [Extension] -> TcM a
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr Extension -> TcM a -> TcM a
forall gbl lcl a. Extension -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
setXOptM TcM a
thing [Extension]
es

    -- See Note [Avoid -Winaccessible-code when deriving]
    unset_warnings_deriving :: TcM a -> TcM a
    unset_warnings_deriving :: forall a. TcM a -> TcM a
unset_warnings_deriving
      | Bool
is_derived = WarningFlag
-> TcRnIf TcGblEnv TcLclEnv a -> TcRnIf TcGblEnv TcLclEnv a
forall gbl lcl a.
WarningFlag -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
unsetWOptM WarningFlag
Opt_WarnInaccessibleCode
      | Bool
otherwise  = TcRnIf TcGblEnv TcLclEnv a -> TcRnIf TcGblEnv TcLclEnv a
forall a. a -> a
id

    hs_sig_fn :: HsSigFun
hs_sig_fn = [LSig GhcRn] -> HsSigFun
mkHsSigFun [LSig GhcRn]
sigs
    inst_loc :: SrcSpan
inst_loc  = Id -> SrcSpan
forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id

    unsat_thetas :: [(Id, Type)]
unsat_thetas =
      (Id -> Maybe (Id, Type)) -> [Id] -> [(Id, Type)]
forall a b. (a -> Maybe b) -> [a] -> [b]
mapMaybe (\ Id
id -> (Id
id,) (Type -> (Id, Type)) -> Maybe Type -> Maybe (Id, Type)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Type -> Maybe Type
isUnsatisfiableCt_maybe (Id -> Type
idType Id
id)) [Id]
dfun_ev_vars

    ----------------------
    tc_item :: ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
    tc_item :: ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_item (Id
sel_id, DefMethInfo
dm_info)
      | Just (LHsBindLR GhcRn GhcRn
user_bind, SrcSpan
bndr_loc, [LSig GhcRn]
prags) <- Name
-> LHsBinds GhcRn
-> TcPragEnv
-> Maybe (LHsBindLR GhcRn GhcRn, SrcSpan, [LSig GhcRn])
findMethodBind (Id -> Name
idName Id
sel_id) LHsBinds GhcRn
binds TcPragEnv
prag_fn
      = SkolemInfoAnon
-> Class
-> [Id]
-> [Id]
-> [Type]
-> TcEvBinds
-> Bool
-> HsSigFun
-> [LTcSpecPrag]
-> [LSig GhcRn]
-> Id
-> LHsBindLR GhcRn GhcRn
-> SrcSpan
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
tcMethodBody SkolemInfoAnon
skol_info Class
clas [Id]
tyvars [Id]
dfun_ev_vars [Type]
inst_tys
                     TcEvBinds
dfun_ev_binds Bool
is_derived HsSigFun
hs_sig_fn
                     [LTcSpecPrag]
spec_inst_prags [LSig GhcRn]
prags
                     Id
sel_id LHsBindLR GhcRn GhcRn
user_bind SrcSpan
bndr_loc
      | Bool
otherwise
      = do { String -> SDoc -> TcRn ()
traceTc String
"tc_def" (Id -> SDoc
forall a. Outputable a => a -> SDoc
ppr Id
sel_id)
           ; Id -> DefMethInfo -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_default Id
sel_id DefMethInfo
dm_info }

    ----------------------
    tc_default :: Id -> DefMethInfo
               -> TcM (TcId, LHsBind GhcTc, Maybe Implication)

    tc_default :: Id -> DefMethInfo -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_default Id
sel_id DefMethInfo
mb_dm = case DefMethInfo
mb_dm of

      -- If the instance has an "Unsatisfiable msg" context,
      -- add method bindings that use "unsatisfiable".
      --
      -- See Note [Implementation of Unsatisfiable constraints],
      -- in GHC.Tc.Errors, point (D).
      DefMethInfo
_ | (Id
theta_id,Type
unsat_msg) : [(Id, Type)]
_ <- [(Id, Type)]
unsat_thetas
        -> do { (meth_id, _) <- Class -> [Id] -> [Id] -> [Type] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars
                                         [Type]
inst_tys Id
sel_id
             ; unsat_id <- tcLookupId unsatisfiableIdName
             -- Recall that unsatisfiable :: forall {rep} (msg :: ErrorMessage) (a :: TYPE rep). Unsatisfiable msg => a
             --
             -- So we need to instantiate the forall and pass the dictionary evidence.
             ; let meth_rhs = SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc' (HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc))
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall a b. (a -> b) -> a -> b
$
                     HsWrapper -> Id -> HsExpr GhcTc
wrapId
                     (   [EvTerm] -> HsWrapper
mkWpEvApps [CoreExpr -> EvTerm
EvExpr (CoreExpr -> EvTerm) -> CoreExpr -> EvTerm
forall a b. (a -> b) -> a -> b
$ Id -> CoreExpr
forall b. Id -> Expr b
Var Id
theta_id]
                     HsWrapper -> HsWrapper -> HsWrapper
<.> [Type] -> HsWrapper
mkWpTyApps [HasDebugCallStack => Type -> Type
Type -> Type
getRuntimeRep Type
meth_tau, Type
unsat_msg, Type
meth_tau])
                     Id
unsat_id
                   meth_bind = IdP GhcTc -> LHsExpr GhcTc -> LHsBind GhcTc
mkVarBind IdP GhcTc
Id
meth_id (LHsExpr GhcTc -> LHsBind GhcTc) -> LHsExpr GhcTc -> LHsBind GhcTc
forall a b. (a -> b) -> a -> b
$ HsWrapper -> LHsExpr GhcTc -> LHsExpr GhcTc
mkLHsWrap HsWrapper
lam_wrapper LHsExpr GhcTc
GenLocated SrcSpanAnnA (HsExpr GhcTc)
meth_rhs
             ; return (meth_id, meth_bind, Nothing) }

      Just (Name
dm_name, DefMethSpec Type
dm_spec) ->
        do { (meth_bind, inline_prags) <- SrcSpan
-> Id
-> Class
-> Id
-> Name
-> DefMethSpec Type
-> TcM (LHsBindLR GhcRn GhcRn, [LSig GhcRn])
mkDefMethBind SrcSpan
inst_loc Id
dfun_id Class
clas Id
sel_id Name
dm_name DefMethSpec Type
dm_spec
           ; tcMethodBody skol_info clas tyvars dfun_ev_vars inst_tys
                          dfun_ev_binds is_derived hs_sig_fn
                          spec_inst_prags inline_prags
                          sel_id meth_bind inst_loc }

      -- No default method
      DefMethInfo
Nothing ->
        do { String -> SDoc -> TcRn ()
traceTc String
"tc_def: warn" (Id -> SDoc
forall a. Outputable a => a -> SDoc
ppr Id
sel_id)
           ; (meth_id, _) <- Class -> [Id] -> [Id] -> [Type] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars
                                       [Type]
inst_tys Id
sel_id
           ; dflags <- getDynFlags
            -- Add a binding whose RHS is an error
            -- "No explicit nor default method for class operation 'meth'".
           ; let meth_rhs  = DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_rhs DynFlags
dflags
                 meth_bind = IdP GhcTc -> LHsExpr GhcTc -> LHsBind GhcTc
mkVarBind IdP GhcTc
Id
meth_id (LHsExpr GhcTc -> LHsBind GhcTc) -> LHsExpr GhcTc -> LHsBind GhcTc
forall a b. (a -> b) -> a -> b
$ HsWrapper -> LHsExpr GhcTc -> LHsExpr GhcTc
mkLHsWrap HsWrapper
lam_wrapper LHsExpr GhcTc
GenLocated SrcSpanAnnA (HsExpr GhcTc)
meth_rhs
           ; return (meth_id, meth_bind, Nothing) }

      where
        inst_loc' :: SrcSpanAnnA
inst_loc' = SrcSpan -> SrcSpanAnnA
forall e. HasAnnotation e => SrcSpan -> e
noAnnSrcSpan SrcSpan
inst_loc
        error_rhs :: DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_rhs DynFlags
dflags = SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc'
                         (HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc))
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall a b. (a -> b) -> a -> b
$ XApp GhcTc -> LHsExpr GhcTc -> LHsExpr GhcTc -> HsExpr GhcTc
forall p. XApp p -> LHsExpr p -> LHsExpr p -> HsExpr p
HsApp XApp GhcTc
NoExtField
noExtField LHsExpr GhcTc
GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_fun (DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_msg DynFlags
dflags)
        error_fun :: GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_fun    = SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc' (HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc))
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall a b. (a -> b) -> a -> b
$
                       HsWrapper -> Id -> HsExpr GhcTc
wrapId ([Type] -> HsWrapper
mkWpTyApps
                                [ HasDebugCallStack => Type -> Type
Type -> Type
getRuntimeRep Type
meth_tau, Type
meth_tau])
                              Id
nO_METHOD_BINDING_ERROR_ID
        error_msg :: DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_msg DynFlags
dflags = SrcSpanAnnA
-> HsExpr GhcTc -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc'
                                    (XLitE GhcTc -> HsLit GhcTc -> HsExpr GhcTc
forall p. XLitE p -> HsLit p -> HsExpr p
HsLit XLitE GhcTc
NoExtField
noExtField (XHsStringPrim GhcTc -> ByteString -> HsLit GhcTc
forall x. XHsStringPrim x -> ByteString -> HsLit x
HsStringPrim XHsStringPrim GhcTc
SourceText
NoSourceText
                                              (String -> ByteString
unsafeMkByteString (DynFlags -> String
error_string DynFlags
dflags))))
        meth_tau :: Type
meth_tau     = Id -> [Type] -> Type
classMethodInstTy Id
sel_id [Type]
inst_tys
        error_string :: DynFlags -> String
error_string DynFlags
dflags = DynFlags -> SDoc -> String
showSDoc DynFlags
dflags
                              ([SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
hcat [SrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr SrcSpan
inst_loc, SDoc
forall doc. IsLine doc => doc
vbar, SDoc -> SDoc
quotes (Id -> SDoc
forall a. Outputable a => a -> SDoc
ppr Id
sel_id) ])
        lam_wrapper :: HsWrapper
lam_wrapper  = [Id] -> HsWrapper
mkWpTyLams [Id]
tyvars HsWrapper -> HsWrapper -> HsWrapper
<.> [Id] -> HsWrapper
mkWpEvLams [Id]
dfun_ev_vars

    ----------------------
    -- Check if one of the minimal complete definitions is satisfied
    checkMinimalDefinition :: TcRn ()
checkMinimalDefinition
      = Bool -> TcRn () -> TcRn ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when ([(Id, Type)] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [(Id, Type)]
unsat_thetas) (TcRn () -> TcRn ()) -> TcRn () -> TcRn ()
forall a b. (a -> b) -> a -> b
$
        -- Don't warn if there is an "Unsatisfiable" constraint in the context.
        --
        -- See Note [Implementation of Unsatisfiable constraints] in GHC.Tc.Errors,
        -- point (D).
        Maybe ClassMinimalDef -> (ClassMinimalDef -> TcRn ()) -> TcRn ()
forall (m :: * -> *) a. Monad m => Maybe a -> (a -> m ()) -> m ()
whenIsJust ((LIdP GhcRn -> Bool) -> ClassMinimalDef -> Maybe ClassMinimalDef
forall (p :: Pass).
Eq (LIdP (GhcPass p)) =>
(LIdP (GhcPass p) -> Bool)
-> BooleanFormula (GhcPass p) -> Maybe (BooleanFormula (GhcPass p))
isUnsatisfied (Name -> Bool
methodExists (Name -> Bool)
-> (GenLocated SrcSpanAnnN Name -> Name)
-> GenLocated SrcSpanAnnN Name
-> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenLocated SrcSpanAnnN Name -> Name
forall l e. GenLocated l e -> e
unLoc) (Class -> ClassMinimalDef
classMinimalDef Class
clas)) ((ClassMinimalDef -> TcRn ()) -> TcRn ())
-> (ClassMinimalDef -> TcRn ()) -> TcRn ()
forall a b. (a -> b) -> a -> b
$
        ClassMinimalDef -> TcRn ()
warnUnsatisfiedMinimalDefinition

    methodExists :: Name -> Bool
methodExists Name
meth = Maybe
  (GenLocated SrcSpanAnnA (HsBind GhcRn), SrcSpan,
   [GenLocated SrcSpanAnnA (Sig GhcRn)])
-> Bool
forall a. Maybe a -> Bool
isJust (Name
-> LHsBinds GhcRn
-> TcPragEnv
-> Maybe (LHsBindLR GhcRn GhcRn, SrcSpan, [LSig GhcRn])
findMethodBind Name
meth LHsBinds GhcRn
binds TcPragEnv
prag_fn)

    ----------------------
    -- Check if any method bindings do not correspond to the class.
    -- See Note [Mismatched class methods and associated type families].
    checkMethBindMembership :: TcRn ()
checkMethBindMembership
      = (Name -> TcRn ()) -> [Name] -> TcRn ()
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ (TcRnMessage -> TcRn ()
addErrTc (TcRnMessage -> TcRn ())
-> (Name -> TcRnMessage) -> Name -> TcRn ()
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> Name -> TcRnMessage
TcRnBadMethodErr (Class -> Name
className Class
clas)) [Name]
mismatched_meths
      where
        bind_nms :: [Name]
bind_nms         = (GenLocated SrcSpanAnnN Name -> Name)
-> [GenLocated SrcSpanAnnN Name] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map GenLocated SrcSpanAnnN Name -> Name
forall l e. GenLocated l e -> e
unLoc ([GenLocated SrcSpanAnnN Name] -> [Name])
-> [GenLocated SrcSpanAnnN Name] -> [Name]
forall a b. (a -> b) -> a -> b
$ LHsBinds GhcRn -> [LIdP GhcRn]
forall idL idR. UnXRec idL => LHsBindsLR idL idR -> [LIdP idL]
collectMethodBinders LHsBinds GhcRn
binds
        cls_meth_nms :: [Name]
cls_meth_nms     = (ClassOpItem -> Name) -> [ClassOpItem] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map (Id -> Name
idName (Id -> Name) -> (ClassOpItem -> Id) -> ClassOpItem -> Name
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ClassOpItem -> Id
forall a b. (a, b) -> a
fst) [ClassOpItem]
op_items
        mismatched_meths :: [Name]
mismatched_meths = [Name]
bind_nms [Name] -> [Name] -> [Name]
forall a. Ord a => [a] -> [a] -> [a]
`minusList` [Name]
cls_meth_nms

{-
Note [Mismatched class methods and associated type families]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's entirely possible for someone to put methods or associated type family
instances inside of a class in which it doesn't belong. For instance, we'd
want to fail if someone wrote this:

  instance Eq () where
    type Rep () = Maybe
    compare = undefined

Since neither the type family `Rep` nor the method `compare` belong to the
class `Eq`. Normally, this is caught in the renamer when resolving RdrNames,
since that would discover that the parent class `Eq` is incorrect.

However, there is a scenario in which the renamer could fail to catch this:
if the instance was generated through Template Haskell, as in #12387. In that
case, Template Haskell will provide fully resolved names (e.g.,
`GHC.Classes.compare`), so the renamer won't notice the sleight-of-hand going
on. For this reason, we also put an extra validity check for this in the
typechecker as a last resort.

Note [Avoid -Winaccessible-code when deriving]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Winaccessible-code can be particularly noisy when deriving instances for
GADTs. Consider the following example (adapted from #8128):

  data T a where
    MkT1 :: Int -> T Int
    MkT2 :: T Bool
    MkT3 :: T Bool
  deriving instance Eq (T a)
  deriving instance Ord (T a)

In the derived Ord instance, GHC will generate the following code:

  instance Ord (T a) where
    compare x y
      = case x of
          MkT2
            -> case y of
                 MkT1 {} -> GT
                 MkT2    -> EQ
                 _       -> LT
          ...

However, that MkT1 is unreachable, since the type indices for MkT1 and MkT2
differ, so if -Winaccessible-code is enabled, then deriving this instance will
result in unwelcome warnings.

One conceivable approach to fixing this issue would be to change `deriving Ord`
such that it becomes smarter about not generating unreachable cases. This,
however, would be a highly nontrivial refactor, as we'd have to propagate
through typing information everywhere in the algorithm that generates Ord
instances in order to determine which cases were unreachable. This seems like
a lot of work for minimal gain, so we have opted not to go for this approach.

Instead, we take the following approach:

1. In tcMethods (which typechecks method bindings), use 'setInGeneratedCode'.
2. When creating Implications during typechecking, record this flag
   (in ic_warn_inaccessible) at the time of creation.
3. After typechecking comes error reporting, where GHC must decide how to
   report inaccessible code to the user, on an Implication-by-Implication
   basis. If the ic_warn_inaccessible field of the Implication is False, then
   we don't bother reporting it. That's it!
-}

------------------------
tcMethodBody :: SkolemInfoAnon
             -> Class -> [TcTyVar] -> [EvVar] -> [TcType]
             -> TcEvBinds -> Bool
             -> HsSigFun
             -> [LTcSpecPrag] -> [LSig GhcRn]
             -> Id -> LHsBind GhcRn -> SrcSpan
             -> TcM (TcId, LHsBind GhcTc, Maybe Implication)
tcMethodBody :: SkolemInfoAnon
-> Class
-> [Id]
-> [Id]
-> [Type]
-> TcEvBinds
-> Bool
-> HsSigFun
-> [LTcSpecPrag]
-> [LSig GhcRn]
-> Id
-> LHsBindLR GhcRn GhcRn
-> SrcSpan
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
tcMethodBody SkolemInfoAnon
skol_info Class
clas [Id]
tyvars [Id]
dfun_ev_vars [Type]
inst_tys
                     TcEvBinds
dfun_ev_binds Bool
is_derived
                     HsSigFun
sig_fn [LTcSpecPrag]
spec_inst_prags [LSig GhcRn]
prags
                     Id
sel_id (L SrcSpanAnnA
bind_loc HsBind GhcRn
meth_bind) SrcSpan
bndr_loc
  = TcM (Id, LHsBind GhcTc, Maybe Implication)
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
add_meth_ctxt (TcM (Id, LHsBind GhcTc, Maybe Implication)
 -> TcM (Id, LHsBind GhcTc, Maybe Implication))
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
forall a b. (a -> b) -> a -> b
$
    do { String -> SDoc -> TcRn ()
traceTc String
"tcMethodBody" (Id -> SDoc
forall a. Outputable a => a -> SDoc
ppr Id
sel_id SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Id -> Type
idType Id
sel_id) SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ SrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr SrcSpan
bndr_loc)
       ; (global_meth_id, local_meth_id) <- SrcSpan -> TcM (Id, Id) -> TcM (Id, Id)
forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan SrcSpan
bndr_loc (TcM (Id, Id) -> TcM (Id, Id)) -> TcM (Id, Id) -> TcM (Id, Id)
forall a b. (a -> b) -> a -> b
$
                                            Class -> [Id] -> [Id] -> [Type] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars
                                                      [Type]
inst_tys Id
sel_id

       ; let lm_bind = HsBind GhcRn
meth_bind { fun_id = L (noAnnSrcSpan bndr_loc)
                                                        (idName local_meth_id) }
                       -- Substitute the local_meth_name for the binder
                       -- NB: the binding is always a FunBind

            -- taking instance signature into account might change the type of
            -- the local_meth_id
       ; (meth_implic, ev_binds_var, tc_bind)
             <- checkInstConstraints skol_info $
                tcMethodBodyHelp sig_fn sel_id local_meth_id (L bind_loc lm_bind)

       ; global_meth_id <- addInlinePrags global_meth_id prags
       ; spec_prags     <- tcSpecPrags global_meth_id prags

        ; let specs  = Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
mk_meth_spec_prags Id
global_meth_id [LTcSpecPrag]
spec_inst_prags [LTcSpecPrag]
spec_prags
              export = ABE { abe_poly :: Id
abe_poly  = Id
global_meth_id
                           , abe_mono :: Id
abe_mono  = Id
local_meth_id
                           , abe_wrap :: HsWrapper
abe_wrap  = HsWrapper
idHsWrapper
                           , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
specs }

              local_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
ev_binds_var
              full_bind = XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall idL idR. XXHsBindsLR idL idR -> HsBindLR idL idR
XHsBindsLR (XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc)
-> XXHsBindsLR GhcTc GhcTc -> HsBindLR GhcTc GhcTc
forall a b. (a -> b) -> a -> b
$
                          AbsBinds { abs_tvs :: [Id]
abs_tvs      = [Id]
tyvars
                                   , abs_ev_vars :: [Id]
abs_ev_vars  = [Id]
dfun_ev_vars
                                   , abs_exports :: [ABExport]
abs_exports  = [ABExport
export]
                                   , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = [TcEvBinds
dfun_ev_binds, TcEvBinds
local_ev_binds]
                                   , abs_binds :: LHsBinds GhcTc
abs_binds    = LHsBinds GhcTc
tc_bind
                                   , abs_sig :: Bool
abs_sig      = Bool
True }

        ; return (global_meth_id, L bind_loc full_bind, Just meth_implic) }
  where
        -- For instance decls that come from deriving clauses
        -- we want to print out the full source code if there's an error
        -- because otherwise the user won't see the code at all
    add_meth_ctxt :: TcM (Id, LHsBind GhcTc, Maybe Implication)
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
add_meth_ctxt TcM (Id, LHsBind GhcTc, Maybe Implication)
thing
      | Bool
is_derived = ErrCtxtMsg
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
forall a. ErrCtxtMsg -> TcM a -> TcM a
addLandmarkErrCtxt (Id -> Class -> [Type] -> ErrCtxtMsg
DerivBindCtxt Id
sel_id Class
clas [Type]
inst_tys) TcM (Id, LHsBind GhcTc, Maybe Implication)
thing
      | Bool
otherwise  = TcM (Id, LHsBind GhcTc, Maybe Implication)
thing

tcMethodBodyHelp :: HsSigFun -> Id -> TcId
                 -> LHsBind GhcRn -> TcM (LHsBinds GhcTc)
tcMethodBodyHelp :: HsSigFun
-> Id -> Id -> LHsBindLR GhcRn GhcRn -> TcM (LHsBinds GhcTc)
tcMethodBodyHelp HsSigFun
hs_sig_fn Id
sel_id Id
local_meth_id LHsBindLR GhcRn GhcRn
meth_bind
  | Just LHsSigType GhcRn
hs_sig_ty <- HsSigFun
hs_sig_fn Name
sel_name
              -- There is a signature in the instance
              -- See Note [Instance method signatures]
  = do { (sig_ty, hs_wrap)
             <- SrcSpan -> TcRn (Type, HsWrapper) -> TcRn (Type, HsWrapper)
forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan (GenLocated SrcSpanAnnA (HsSigType GhcRn) -> SrcSpan
forall a e. HasLoc a => GenLocated a e -> SrcSpan
getLocA LHsSigType GhcRn
GenLocated SrcSpanAnnA (HsSigType GhcRn)
hs_sig_ty) (TcRn (Type, HsWrapper) -> TcRn (Type, HsWrapper))
-> TcRn (Type, HsWrapper) -> TcRn (Type, HsWrapper)
forall a b. (a -> b) -> a -> b
$
                do { inst_sigs <- Extension -> TcRn Bool
forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.InstanceSigs
                   ; checkTc inst_sigs (TcRnMisplacedInstSig sel_name hs_sig_ty)
                   ; let ctxt = Name -> ReportRedundantConstraints -> UserTypeCtxt
FunSigCtxt Name
sel_name ReportRedundantConstraints
NoRRC
                   ; sig_ty  <- tcHsSigType ctxt hs_sig_ty
                   ; let local_meth_ty = Id -> Type
idType Id
local_meth_id
                                -- False <=> do not report redundant constraints when
                                --           checking instance-sig <= class-meth-sig
                                -- The instance-sig is the focus here; the class-meth-sig
                                -- is fixed (#18036)
                   ; let orig = Name -> Type -> Type -> CtOrigin
InstanceSigOrigin Name
sel_name Type
sig_ty Type
local_meth_ty
                   ; hs_wrap <- addErrCtxtM (methSigCtxt sel_name sig_ty local_meth_ty) $
                                tcSubTypeSigma orig ctxt sig_ty local_meth_ty
                   ; return (sig_ty, hs_wrap) }

       ; inner_meth_name <- newName (nameOccName sel_name)
       ; let ctxt = Name -> ReportRedundantConstraints -> UserTypeCtxt
FunSigCtxt Name
sel_name (LHsSigType GhcRn -> ReportRedundantConstraints
lhsSigTypeContextSpan LHsSigType GhcRn
hs_sig_ty)
                    -- WantRCC <=> check for redundant constraints in the
                    --          user-specified instance signature
             inner_meth_id  = HasDebugCallStack => Name -> Type -> Type -> Id
Name -> Type -> Type -> Id
mkLocalId Name
inner_meth_name Type
ManyTy Type
sig_ty
             inner_meth_sig = CSig { sig_bndr :: Id
sig_bndr = Id
inner_meth_id
                                   , sig_ctxt :: UserTypeCtxt
sig_ctxt = UserTypeCtxt
ctxt
                                   , sig_loc :: SrcSpan
sig_loc  = GenLocated SrcSpanAnnA (HsSigType GhcRn) -> SrcSpan
forall a e. HasLoc a => GenLocated a e -> SrcSpan
getLocA LHsSigType GhcRn
GenLocated SrcSpanAnnA (HsSigType GhcRn)
hs_sig_ty }

       ; (tc_bind, [Scaled _ inner_id]) <- tcPolyCheck no_prag_fn inner_meth_sig meth_bind

       ; let export = ABE { abe_poly :: Id
abe_poly  = Id
local_meth_id
                          , abe_mono :: Id
abe_mono  = Id
inner_id
                          , abe_wrap :: HsWrapper
abe_wrap  = HsWrapper
hs_wrap
                          , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
noSpecPrags }

       ; return (singleton $ L (getLoc meth_bind) $ XHsBindsLR $
                 AbsBinds { abs_tvs = [], abs_ev_vars = []
                          , abs_exports = [export]
                          , abs_binds = tc_bind, abs_ev_binds = []
                          , abs_sig = True }) }

  | Bool
otherwise  -- No instance signature
  = do { let ctxt :: UserTypeCtxt
ctxt = Name -> ReportRedundantConstraints -> UserTypeCtxt
FunSigCtxt Name
sel_name ReportRedundantConstraints
NoRRC
                    -- NoRRC <=> don't report redundant constraints
                    -- The signature is not under the users control!
             tc_sig :: TcCompleteSig
tc_sig = UserTypeCtxt -> Id -> TcCompleteSig
completeSigFromId UserTypeCtxt
ctxt Id
local_meth_id
              -- Absent a type sig, there are no new scoped type variables here
              -- Only the ones from the instance decl itself, which are already
              -- in scope.  Example:
              --      class C a where { op :: forall b. Eq b => ... }
              --      instance C [c] where { op = <rhs> }
              -- In <rhs>, 'c' is scope but 'b' is not!

       ; (tc_bind, _) <- TcPragEnv
-> TcCompleteSig
-> LHsBindLR GhcRn GhcRn
-> TcM (LHsBinds GhcTc, [Scaled Id])
tcPolyCheck TcPragEnv
NameEnv [GenLocated SrcSpanAnnA (Sig GhcRn)]
no_prag_fn TcCompleteSig
tc_sig LHsBindLR GhcRn GhcRn
meth_bind
       ; return tc_bind }

  where
    sel_name :: Name
sel_name   = Id -> Name
idName Id
sel_id
    no_prag_fn :: TcPragEnv
no_prag_fn = TcPragEnv
emptyPragEnv   -- No pragmas for local_meth_id;
                                -- they are all for meth_id

------------------------
mkMethIds :: Class -> [TcTyVar] -> [EvVar]
          -> [TcType] -> Id -> TcM (TcId, TcId)
             -- returns (poly_id, local_id), but ignoring any instance signature
             -- See Note [Instance method signatures]
mkMethIds :: Class -> [Id] -> [Id] -> [Type] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars [Type]
inst_tys Id
sel_id
  = do  { poly_meth_name  <- OccName -> TcM Name
newName (OccName -> OccName
mkClassOpAuxOcc OccName
sel_occ)
        ; local_meth_name <- newName sel_occ
                  -- Base the local_meth_name on the selector name, because
                  -- type errors from tcMethodBody come from here
        ; let poly_meth_id  = HasDebugCallStack => Name -> Type -> Type -> Id
Name -> Type -> Type -> Id
mkLocalId Name
poly_meth_name  Type
ManyTy Type
poly_meth_ty
              local_meth_id = HasDebugCallStack => Name -> Type -> Type -> Id
Name -> Type -> Type -> Id
mkLocalId Name
local_meth_name Type
ManyTy Type
local_meth_ty

        ; return (poly_meth_id, local_meth_id) }
  where
    sel_name :: Name
sel_name      = Id -> Name
idName Id
sel_id
    -- Force so that a thunk doesn't end up in a Name (#19619)
    !sel_occ :: OccName
sel_occ      = Name -> OccName
nameOccName Name
sel_name
    local_meth_ty :: Type
local_meth_ty = Class -> Id -> [Type] -> Type
instantiateMethod Class
clas Id
sel_id [Type]
inst_tys
    poly_meth_ty :: Type
poly_meth_ty  = [Id] -> [Type] -> Type -> Type
HasDebugCallStack => [Id] -> [Type] -> Type -> Type
mkSpecSigmaTy [Id]
tyvars [Type]
theta Type
local_meth_ty
    theta :: [Type]
theta         = (Id -> Type) -> [Id] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map Id -> Type
idType [Id]
dfun_ev_vars

methSigCtxt :: Name -> TcType -> TcType -> TidyEnv -> ZonkM (TidyEnv, ErrCtxtMsg)
methSigCtxt :: Name -> Type -> Type -> TidyEnv -> ZonkM (TidyEnv, ErrCtxtMsg)
methSigCtxt Name
sel_name Type
sig_ty Type
meth_ty TidyEnv
env0
  = do { (env1, sig_ty)  <- TidyEnv -> Type -> ZonkM (TidyEnv, Type)
zonkTidyTcType TidyEnv
env0 Type
sig_ty
       ; (env2, meth_ty) <- zonkTidyTcType env1 meth_ty
       ; return (env2, MethSigCtxt sel_name sig_ty meth_ty) }

{- Note [Instance method signatures]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With -XInstanceSigs we allow the user to supply a signature for the
method in an instance declaration.  Here is an artificial example:

       data T a = MkT a
       instance Ord a => Ord (T a) where
         (>) :: forall b. b -> b -> Bool
         (>) = error "You can't compare Ts"

The instance signature can be *more* polymorphic than the instantiated
class method (in this case: Age -> Age -> Bool), but it cannot be less
polymorphic.  Moreover, if a signature is given, the implementation
code should match the signature, and type variables bound in the
signature should scope over the method body.

We achieve this by building a TcSigInfo for the method, whether or not
there is an instance method signature, and using that to typecheck
the declaration (in tcMethodBody).  That means, conveniently,
that the type variables bound in the signature will scope over the body.

What about the check that the instance method signature is more
polymorphic than the instantiated class method type?  We just do a
tcSubType call in tcMethodBodyHelp, and generate a nested AbsBind, like
this (for the example above

 AbsBind { abs_tvs = [a], abs_ev_vars = [d:Ord a]
         , abs_exports
             = ABExport { (>) :: forall a. Ord a => T a -> T a -> Bool
                        , gr_lcl :: T a -> T a -> Bool }
         , abs_binds
             = AbsBind { abs_tvs = [], abs_ev_vars = []
                       , abs_exports = ABExport { gr_lcl :: T a -> T a -> Bool
                                                , gr_inner :: forall b. b -> b -> Bool }
                       , abs_binds = AbsBind { abs_tvs = [b], abs_ev_vars = []
                                             , ..etc.. }
               } }

Wow!  Three nested AbsBinds!
 * The outer one abstracts over the tyvars and dicts for the instance
 * The middle one is only present if there is an instance signature,
   and does the impedance matching for that signature
 * The inner one is for the method binding itself against either the
   signature from the class, or the instance signature.
-}

----------------------
mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
        -- Adapt the 'SPECIALISE instance' pragmas to work for this method Id
        -- There are two sources:
        --   * spec_prags_for_me: {-# SPECIALISE op :: <blah> #-}
        --   * spec_prags_from_inst: derived from {-# SPECIALISE instance :: <blah> #-}
        --     These ones have the dfun inside, but [perhaps surprisingly]
        --     the correct wrapper.
        -- See Note [Handling SPECIALISE pragmas] in GHC.Tc.Gen.Bind
mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
mk_meth_spec_prags Id
meth_id [LTcSpecPrag]
spec_inst_prags [LTcSpecPrag]
spec_prags_for_me
  = [LTcSpecPrag] -> TcSpecPrags
SpecPrags ([LTcSpecPrag]
spec_prags_for_me [LTcSpecPrag] -> [LTcSpecPrag] -> [LTcSpecPrag]
forall a. [a] -> [a] -> [a]
++ [LTcSpecPrag]
spec_prags_from_inst)
  where
    spec_prags_from_inst :: [LTcSpecPrag]
spec_prags_from_inst
       | InlinePragma -> Bool
isInlinePragma (Id -> InlinePragma
idInlinePragma Id
meth_id)
       = []  -- Do not inherit SPECIALISE from the instance if the
             -- method is marked INLINE, because then it'll be inlined
             -- and the specialisation would do nothing. (Indeed it'll provoke
             -- a warning from the desugarer
       | Bool
otherwise
       = [ SrcSpan -> TcSpecPrag -> LTcSpecPrag
forall l e. l -> e -> GenLocated l e
L SrcSpan
inst_loc (Id -> HsWrapper -> InlinePragma -> TcSpecPrag
SpecPrag Id
meth_id HsWrapper
wrap InlinePragma
inl)
         | L SrcSpan
inst_loc (SpecPrag Id
_       HsWrapper
wrap InlinePragma
inl) <- [LTcSpecPrag]
spec_inst_prags]


mkDefMethBind :: SrcSpan -> DFunId -> Class -> Id -> Name
              -> DefMethSpec Type
              -> TcM (LHsBind GhcRn, [LSig GhcRn])
-- The is a default method (vanailla or generic) defined in the class
-- So make a binding   op @m1 @m2 @m3 = $dmop @i1 @i2 @m1 @m2 @m3
-- where $dmop is the name of the default method in the class;
-- i1 and t2 are the instance types; and m1, m2, and m3 are the type variables
-- from the method's type signature. See Note [Default methods in instances] for
-- why we use visible type application here.
mkDefMethBind :: SrcSpan
-> Id
-> Class
-> Id
-> Name
-> DefMethSpec Type
-> TcM (LHsBindLR GhcRn GhcRn, [LSig GhcRn])
mkDefMethBind SrcSpan
loc Id
dfun_id Class
clas Id
sel_id Name
dm_name DefMethSpec Type
dm_spec
  = do  { logger <- IOEnv (Env TcGblEnv TcLclEnv) Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
        ; dm_id <- tcLookupId dm_name
        ; let inline_prag = Id -> InlinePragma
idInlinePragma Id
dm_id
              inline_prags | InlinePragma -> Bool
isAnyInlinePragma InlinePragma
inline_prag
                           = [Sig GhcRn -> GenLocated SrcSpanAnnA (Sig GhcRn)
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA (XInlineSig GhcRn -> LIdP GhcRn -> InlinePragma -> Sig GhcRn
forall pass.
XInlineSig pass -> LIdP pass -> InlinePragma -> Sig pass
InlineSig (EpaLocation, EpToken "#-}", ActivationAnn)
XInlineSig GhcRn
forall a. NoAnn a => a
noAnn LIdP GhcRn
GenLocated SrcSpanAnnN Name
fn InlinePragma
inline_prag)]
                           | Bool
otherwise
                           = []
                 -- Copy the inline pragma (if any) from the default method
                 -- to this version. Note [INLINE and default methods]

        ; liftIO (putDumpFileMaybe logger Opt_D_dump_deriv "Filling in method body"
                   FormatHaskell
                   (vcat [ppr clas <+> ppr inst_tys,
                          nest 2 (ppr bind)]))

       ; return (bind, inline_prags) }
  where
    ([Id]
_, [Type]
_, Class
_, [Type]
inst_tys) = Type -> ([Id], [Type], Class, [Type])
tcSplitDFunTy (Id -> Type
idType Id
dfun_id)
    ([Id]
_, Type
_, Type
sel_tau) = Type -> ([Id], Type, Type)
tcSplitMethodTy (Id -> Type
idType Id
sel_id)
    ([TcInvisTVBinder]
sel_tvbs, Type
_) = Type -> ([TcInvisTVBinder], Type)
tcSplitForAllInvisTVBinders Type
sel_tau

    -- Compute the instance types to use in the visible type application. See
    -- Note [Default methods in instances].
    visible_inst_tys :: [Type]
visible_inst_tys =
      [ Type
ty | (TyConBinder
tcb, Type
ty) <- TyCon -> [TyConBinder]
tyConBinders (Class -> TyCon
classTyCon Class
clas) [TyConBinder] -> [Type] -> [(TyConBinder, Type)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Type]
inst_tys
           , TyConBinder -> ForAllTyFlag
forall a. VarBndr a TyConBndrVis -> ForAllTyFlag
tyConBinderForAllTyFlag TyConBinder
tcb ForAllTyFlag -> ForAllTyFlag -> Bool
forall a. Eq a => a -> a -> Bool
/= ForAllTyFlag
Inferred ]

    visible_sel_tvbs :: [TcInvisTVBinder]
visible_sel_tvbs =
      case DefMethSpec Type
dm_spec of
        -- When dealing with a vanilla default method, compute the type
        -- variables from the method's type signature. That way, we can bind
        -- them with TypeAbstractions (visible_sel_pats) and use them in the
        -- visible type application (visible_sel_tys). See Note [Default methods
        -- in instances] (Wrinkle: Ambiguous types from vanilla method type
        -- signatures).
        DefMethSpec Type
VanillaDM -> (TcInvisTVBinder -> Bool) -> [TcInvisTVBinder] -> [TcInvisTVBinder]
forall a. (a -> Bool) -> [a] -> [a]
filter (\TcInvisTVBinder
tvb -> TcInvisTVBinder -> Specificity
forall tv argf. VarBndr tv argf -> argf
binderFlag TcInvisTVBinder
tvb Specificity -> Specificity -> Bool
forall a. Eq a => a -> a -> Bool
/= Specificity
InferredSpec) [TcInvisTVBinder]
sel_tvbs
        -- If we are dealing with a generic default method, on the other hand,
        -- don't bother doing any of this. See Note [Default methods
        -- in instances] (Wrinkle: Ambiguous types from generic default method
        -- type signatures).
        GenericDM {} -> []
    visible_sel_pats :: [GenLocated SrcSpanAnnA (Pat GhcRn)]
visible_sel_pats = (TcInvisTVBinder -> GenLocated SrcSpanAnnA (Pat GhcRn))
-> [TcInvisTVBinder] -> [GenLocated SrcSpanAnnA (Pat GhcRn)]
forall a b. (a -> b) -> [a] -> [b]
map TcInvisTVBinder -> LPat GhcRn
TcInvisTVBinder -> GenLocated SrcSpanAnnA (Pat GhcRn)
mk_ty_pat [TcInvisTVBinder]
visible_sel_tvbs
    visible_sel_tys :: [Type]
visible_sel_tys = (TcInvisTVBinder -> Type) -> [TcInvisTVBinder] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map (Id -> Type
mkTyVarTy (Id -> Type) -> (TcInvisTVBinder -> Id) -> TcInvisTVBinder -> Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TcInvisTVBinder -> Id
forall tv argf. VarBndr tv argf -> tv
binderVar) [TcInvisTVBinder]
visible_sel_tvbs

    fn :: GenLocated SrcSpanAnnN Name
fn   = Name -> GenLocated SrcSpanAnnN Name
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA (Id -> Name
idName Id
sel_id)
    rhs :: LocatedA (HsExpr GhcRn)
rhs  = (LocatedA (HsExpr GhcRn) -> Type -> LocatedA (HsExpr GhcRn))
-> LocatedA (HsExpr GhcRn) -> [Type] -> LocatedA (HsExpr GhcRn)
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' LHsExpr GhcRn -> Type -> LHsExpr GhcRn
LocatedA (HsExpr GhcRn) -> Type -> LocatedA (HsExpr GhcRn)
mk_vta (IdP GhcRn -> LHsExpr GhcRn
forall (p :: Pass) a.
IsSrcSpanAnn p a =>
IdP (GhcPass p) -> LHsExpr (GhcPass p)
nlHsVar IdP GhcRn
Name
dm_name) ([Type] -> LocatedA (HsExpr GhcRn))
-> [Type] -> LocatedA (HsExpr GhcRn)
forall a b. (a -> b) -> a -> b
$
           [Type]
visible_inst_tys [Type] -> [Type] -> [Type]
forall a. [a] -> [a] -> [a]
++ [Type]
visible_sel_tys
    bind :: GenLocated SrcSpanAnnA (HsBind GhcRn)
bind = SrcSpanAnnA
-> HsBind GhcRn -> GenLocated SrcSpanAnnA (HsBind GhcRn)
forall l e. l -> e -> GenLocated l e
L (SrcSpan -> SrcSpanAnnA
forall e. HasAnnotation e => SrcSpan -> e
noAnnSrcSpan SrcSpan
loc)
          (HsBind GhcRn -> GenLocated SrcSpanAnnA (HsBind GhcRn))
-> HsBind GhcRn -> GenLocated SrcSpanAnnA (HsBind GhcRn)
forall a b. (a -> b) -> a -> b
$ Origin
-> GenLocated SrcSpanAnnN Name
-> [LMatch GhcRn (LHsExpr GhcRn)]
-> HsBind GhcRn
mkTopFunBind (GenReason -> DoPmc -> Origin
Generated GenReason
OtherExpansion DoPmc
SkipPmc) GenLocated SrcSpanAnnN Name
fn
              [HsMatchContext (LIdP (NoGhcTc GhcRn))
-> LocatedE [LPat GhcRn]
-> LocatedA (HsExpr GhcRn)
-> LMatch GhcRn (LocatedA (HsExpr GhcRn))
forall (p :: Pass) (body :: * -> *).
(Anno (Match (GhcPass p) (LocatedA (body (GhcPass p))))
 ~ SrcSpanAnnA,
 Anno (GRHS (GhcPass p) (LocatedA (body (GhcPass p))))
 ~ EpAnn NoEpAnns) =>
HsMatchContext (LIdP (NoGhcTc (GhcPass p)))
-> LocatedE [LPat (GhcPass p)]
-> LocatedA (body (GhcPass p))
-> LMatch (GhcPass p) (LocatedA (body (GhcPass p)))
mkSimpleMatch (GenLocated SrcSpanAnnN Name
-> AnnFunRhs -> HsMatchContext (GenLocated SrcSpanAnnN Name)
forall fn. fn -> AnnFunRhs -> HsMatchContext fn
mkPrefixFunRhs GenLocated SrcSpanAnnN Name
fn AnnFunRhs
forall a. NoAnn a => a
noAnn) ([GenLocated SrcSpanAnnA (Pat GhcRn)]
-> GenLocated EpaLocation [GenLocated SrcSpanAnnA (Pat GhcRn)]
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA [GenLocated SrcSpanAnnA (Pat GhcRn)]
visible_sel_pats) LocatedA (HsExpr GhcRn)
rhs]

    mk_ty_pat :: VarBndr TyVar Specificity -> LPat GhcRn
    mk_ty_pat :: TcInvisTVBinder -> LPat GhcRn
mk_ty_pat (Bndr Id
tv Specificity
spec) =
      Pat GhcRn -> GenLocated SrcSpanAnnA (Pat GhcRn)
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA (Pat GhcRn -> GenLocated SrcSpanAnnA (Pat GhcRn))
-> Pat GhcRn -> GenLocated SrcSpanAnnA (Pat GhcRn)
forall a b. (a -> b) -> a -> b
$
      XInvisPat GhcRn -> HsTyPat (NoGhcTc GhcRn) -> Pat GhcRn
forall p. XInvisPat p -> HsTyPat (NoGhcTc p) -> Pat p
InvisPat XInvisPat GhcRn
Specificity
spec (HsTyPat (NoGhcTc GhcRn) -> Pat GhcRn)
-> HsTyPat (NoGhcTc GhcRn) -> Pat GhcRn
forall a b. (a -> b) -> a -> b
$
      XHsTP (NoGhcTc GhcRn)
-> LHsType (NoGhcTc GhcRn) -> HsTyPat (NoGhcTc GhcRn)
forall pass. XHsTP pass -> LHsType pass -> HsTyPat pass
HsTP ([Name] -> [Name] -> [Name] -> HsTyPatRn
HsTPRn [] [Id -> Name
tyVarName Id
tv] []) (LHsType (NoGhcTc GhcRn) -> HsTyPat (NoGhcTc GhcRn))
-> LHsType (NoGhcTc GhcRn) -> HsTyPat (NoGhcTc GhcRn)
forall a b. (a -> b) -> a -> b
$
      PromotionFlag -> IdP GhcRn -> LHsKind GhcRn
forall (p :: Pass) a.
IsSrcSpanAnn p a =>
PromotionFlag -> IdP (GhcPass p) -> LHsType (GhcPass p)
nlHsTyVar PromotionFlag
NotPromoted (IdP GhcRn -> LHsKind GhcRn) -> IdP GhcRn -> LHsKind GhcRn
forall a b. (a -> b) -> a -> b
$
      Id -> Name
tyVarName Id
tv

    mk_vta :: LHsExpr GhcRn -> Type -> LHsExpr GhcRn
    mk_vta :: LHsExpr GhcRn -> Type -> LHsExpr GhcRn
mk_vta LHsExpr GhcRn
fun Type
ty = HsExpr GhcRn -> LocatedA (HsExpr GhcRn)
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA (XAppTypeE GhcRn
-> LHsExpr GhcRn -> LHsWcType (NoGhcTc GhcRn) -> HsExpr GhcRn
forall p.
XAppTypeE p -> LHsExpr p -> LHsWcType (NoGhcTc p) -> HsExpr p
HsAppType XAppTypeE GhcRn
NoExtField
noExtField LHsExpr GhcRn
fun
        (LHsKind GhcRn -> HsWildCardBndrs GhcRn (LHsKind GhcRn)
forall thing. thing -> HsWildCardBndrs GhcRn thing
mkEmptyWildCardBndrs (LHsKind GhcRn -> HsWildCardBndrs GhcRn (LHsKind GhcRn))
-> LHsKind GhcRn -> HsWildCardBndrs GhcRn (LHsKind GhcRn)
forall a b. (a -> b) -> a -> b
$ Type -> LHsKind GhcRn
type_to_hs_type Type
ty))
       -- NB: use visible type application
       -- See Note [Default methods in instances]

    type_to_hs_type :: Type -> LHsType GhcRn
    type_to_hs_type :: Type -> LHsKind GhcRn
type_to_hs_type = PprPrec -> LHsKind GhcRn -> LHsKind GhcRn
forall (p :: Pass).
PprPrec -> LHsType (GhcPass p) -> LHsType (GhcPass p)
parenthesizeHsType PprPrec
appPrec (GenLocated SrcSpanAnnA (HsType GhcRn)
 -> GenLocated SrcSpanAnnA (HsType GhcRn))
-> (Type -> GenLocated SrcSpanAnnA (HsType GhcRn))
-> Type
-> GenLocated SrcSpanAnnA (HsType GhcRn)
forall b c a. (b -> c) -> (a -> b) -> a -> c
. HsType GhcRn -> GenLocated SrcSpanAnnA (HsType GhcRn)
forall e a. HasAnnotation e => a -> GenLocated e a
noLocA (HsType GhcRn -> GenLocated SrcSpanAnnA (HsType GhcRn))
-> (Type -> HsType GhcRn)
-> Type
-> GenLocated SrcSpanAnnA (HsType GhcRn)
forall b c a. (b -> c) -> (a -> b) -> a -> c
. XXType GhcRn -> HsType GhcRn
Type -> HsType GhcRn
forall pass. XXType pass -> HsType pass
XHsType

----------------------

warnUnsatisfiedMinimalDefinition :: ClassMinimalDef -> TcM ()
warnUnsatisfiedMinimalDefinition :: ClassMinimalDef -> TcRn ()
warnUnsatisfiedMinimalDefinition ClassMinimalDef
mindef
  = do { warn <- WarningFlag -> TcRn Bool
forall gbl lcl. WarningFlag -> TcRnIf gbl lcl Bool
woptM WarningFlag
Opt_WarnMissingMethods
       ; let msg = ClassMinimalDef -> TcRnMessage
TcRnUnsatisfiedMinimalDef ClassMinimalDef
mindef
       ; diagnosticTc warn msg
       }

{-
Note [Export helper functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We arrange to export the "helper functions" of an instance declaration,
so that they are not subject to preInlineUnconditionally, even if their
RHS is trivial.  Reason: they are mentioned in the DFunUnfolding of
the dict fun as Ids, not as CoreExprs, so we can't substitute a
non-variable for them.

We could change this by making DFunUnfoldings have CoreExprs, but it
seems a bit simpler this way.

Note [Default methods in instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this

   class Baz v x where
      foo :: x -> x
      foo y = <blah>

   instance Baz Int Int

From the class decl we get

   $dmfoo :: forall v x. Baz v x => x -> x
   $dmfoo y = <blah>

Notice that the type of `v` is ambiguous.  So we use Visible Type Application
(VTA) to disambiguate:

   $dBazIntInt = MkBaz fooIntInt
   fooIntInt = $dmfoo @Int @Int

Lacking VTA we'd get ambiguity errors involving the default method.  This applies
equally to vanilla default methods (#1061) and generic default methods
(#12220).

Historical note: before we had VTA we had to generate
post-type-checked code, which took a lot more code, and didn't work for
generic default methods.

-----
-- Wrinkle: Ambiguous types from vanilla method type signatures
-----

In the Bar example above, the ambiguity arises from `v`, a type variable
arising from the class header. It is also possible for the ambiguity to arise
from a type variable bound by the method's type signature itself (see #14266
and #25148). For example:

   class A t where
      f :: forall x m. Monoid x => t m -> m
      f = <blah>

   instance A []

The class declaration gives rise to the following default function:

  $dmf :: forall t. A t => forall x m. Monoid x => t m -> m
  $dmf = <blah>

And the instance declaration gives rise to generated code that looks roughly
like this:

   instance A [] where
      f = $dmf @[] ...

In this example, it is not enough to use VTA to specify the type of `t`, since
the type of `x` (bound by `f`'s type signature) is also ambiguous. We need to
generate code that looks more like this:

   instance A [] where
      f = $dmf @[] @x @m

But where should `x` and `m` be bound? It's tempting to use ScopedTypeVariables
and InstanceSigs to accomplish this:

   instance A [] where
      f :: forall x m. Monoid x => [m] -> m
      f = $dmf @[] @x @m

GHC will reject this code, however, as the type signature for `f` will fail the
subtype check for InstanceSigs:

    • Could not deduce (Monoid x0)
      from the context: Monoid x
        bound by the type signature for:
                   f :: forall x m. Monoid x => [m] -> m
      The type variable ‘x0’ is ambiguous
    • When checking that instance signature for ‘f’
        is more general than its signature in the class
        Instance sig: forall x m. Monoid x => [m] -> m
           Class sig: forall x m. Monoid x => [m] -> m
      In the instance declaration for ‘A []’

See #17898. To avoid this problem, we instead bind `x` and `m` using
TypeAbstractions:

   instance A [] where
      f @x @m = $dmf @[] @x @m

This resolves the ambiguity and avoids the need for a subtype check. (We also
use a similar trick for resolving ambiguity in GeneralizedNewtypeDeriving: see
also Note [GND and ambiguity] in GHC.Tc.Deriv.Generate.)

-----
-- Wrinkle: Ambiguous types from generic default method type signatures
-----

Note that the approach described above (in Wrinkle: Ambiguous types from
vanilla method type signatures) will only work for vanilla default methods and
/not/ for generic default methods (i.e., methods using DefaultSignatures). This
is because for vanilla default methods, the type of the generated $dm* function
will always quantify the same type variables as the method's original type
signature, in the same order and with the same specificities. For example, the
type of the $dmf function will be:

   $dmf :: forall t. A t => forall x m. Monoid x => t m -> m

As such, it is guaranteed that the type variables from the method's original
type signature will line up exactly with the type variables from the $dm*
function (after instantiating all of the class variables):

   instance A [] where
      f @x @m = $dmf @[] @x @m

We cannot guarantee this property for generic default methods, however. As
such, we must be more conservative and generate code without instantiating any
of the type variables bound by the method's type signature (only the type
variables bound by the class header):

   instance A [] where
      f = $dmf @[]

There are a number of reasons why we cannot reliably instantiate the type
variables bound by a generic default method's type signature:

* Default methods can quantify type variables in a different order, e.g.,

    class A t where
       f :: forall x m. Monoid x => t m -> m
       default f :: forall m x. Monoid x => t m -> m
       f = <blah>

  Note that the default signature quantifies the type variables in the opposite
  order from the method's original type signature. As such, the type of $dmf
  will be:

    $dmf :: forall t. A t => forall m x. Monoid x => t m -> m

  Therefore, `f @x @m = $dmf @[] @x @m` would be incorrect. Nor would it be
  straightforward to infer what the correct order of type variables should be.

* Default methods can quantify a different number of type variables, e.g.,

    class A t where
       f :: forall x m. Monoid x => t m -> m
       default f :: forall p q r m. C a t p q r => t m -> m
       f = <blah>

  This gives rise to:

    $dmf :: forall t. A t => forall p q r m. C a t p q r => t m -> m

  And thus generating `f @x @m = $dmf @[] @x @m` would be incorrect, for
  similar reasons as in the example above.

* Default methods can use different type variable specificities, e.g.,

    class A t where
       f :: forall x m. Monoid x => t m -> m
       default f :: forall {x} m. Monoid x => t m -> m
       f = <blah>

  This gives rise to:

    $dmf :: forall t. A t => forall {x} m. Monoid x => t m -> m

  Therefore, generating `f @x @m = $dmf @[] @x @m` would be incorrect because
  the `x` in the type of $dmf is inferred, so it is not eligible for visible
  type application.

As such, we do not bother trying to resolve the ambiguity of any method-bound
type variables when dealing with generic defaults. This means that GHC won't be
able to typecheck the default method examples above, but so be it.

Note [INLINE and default methods]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Default methods need special case.  They are supposed to behave rather like
macros.  For example

  class Foo a where
    op1, op2 :: Bool -> a -> a

    {-# INLINE op1 #-}
    op1 b x = op2 (not b) x

  instance Foo Int where
    -- op1 via default method
    op2 b x = <blah>

The instance declaration should behave

   just as if 'op1' had been defined with the
   code, and INLINE pragma, from its original
   definition.

That is, just as if you'd written

  instance Foo Int where
    op2 b x = <blah>

    {-# INLINE op1 #-}
    op1 b x = op2 (not b) x

So for the above example we generate:

  {-# INLINE $dmop1 #-}
  -- $dmop1 has an InlineCompulsory unfolding
  $dmop1 d b x = op2 d (not b) x

  $fFooInt = MkD $cop1 $cop2

  {-# INLINE $cop1 #-}
  $cop1 = $dmop1 $fFooInt

  $cop2 = <blah>

Note carefully:

* We *copy* any INLINE pragma from the default method $dmop1 to the
  instance $cop1.  Otherwise we'll just inline the former in the
  latter and stop, which isn't what the user expected

* Regardless of its pragma, we give the default method an
  unfolding with an InlineCompulsory source. That means
  that it'll be inlined at every use site, notably in
  each instance declaration, such as $cop1.  This inlining
  must happen even though
    a) $dmop1 is not saturated in $cop1
    b) $cop1 itself has an INLINE pragma

  It's vital that $dmop1 *is* inlined in this way, to allow the mutual
  recursion between $fooInt and $cop1 to be broken

* To communicate the need for an InlineCompulsory to the desugarer
  (which makes the Unfoldings), we use the IsDefaultMethod constructor
  in TcSpecPrags.


************************************************************************
*                                                                      *
        Specialise instance pragmas
*                                                                      *
************************************************************************

Note [SPECIALISE instance pragmas]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider

   instance (Ix a, Ix b) => Ix (a,b) where
     {-# SPECIALISE instance Ix (Int,Int) #-}
     range (x,y) = ...

We make a specialised version of the dictionary function, AND
specialised versions of each *method*.  Thus we should generate
something like this:

  $dfIxPair :: (Ix a, Ix b) => Ix (a,b)
  {-# DFUN [$crangePair, ...] #-}
  {-# SPECIALISE $dfIxPair :: Ix (Int,Int) #-}
  $dfIxPair da db = Ix ($crangePair da db) (...other methods...)

  $crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)]
  {-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-}
  $crange da db = <blah>

The SPECIALISE pragmas are acted upon by the desugarer, which generate

  dii :: Ix Int
  dii = ...

  $s$dfIxPair :: Ix ((Int,Int),(Int,Int))
  {-# DFUN [$crangePair di di, ...] #-}
  $s$dfIxPair = Ix ($crangePair di di) (...)

  {-# RULE forall (d1,d2:Ix Int). $dfIxPair Int Int d1 d2 = $s$dfIxPair #-}

  $s$crangePair :: ((Int,Int),(Int,Int)) -> [(Int,Int)]
  $c$crangePair = ...specialised RHS of $crangePair...

  {-# RULE forall (d1,d2:Ix Int). $crangePair Int Int d1 d2 = $s$crangePair #-}

Note that

  * The specialised dictionary $s$dfIxPair is very much needed, in case we
    call a function that takes a dictionary, but in a context where the
    specialised dictionary can be used.  See #7797.

  * The ClassOp rule for 'range' works equally well on $s$dfIxPair, because
    it still has a DFunUnfolding.  See Note [ClassOp/DFun selection]

  * A call (range ($dfIxPair Int Int d1 d2)) might simplify two ways:
       --> {ClassOp rule for range}     $crangePair Int Int d1 d2
       --> {SPEC rule for $crangePair}  $s$crangePair
    or thus:
       --> {SPEC rule for $dfIxPair}    range $s$dfIxPair
       --> {ClassOpRule for range}      $s$crangePair
    It doesn't matter which way.

  * We want to specialise the RHS of both $dfIxPair and $crangePair,
    but the SAME HsWrapper will do for both!  We can call tcSpecPrag
    just once, and pass the result (in spec_inst_info) to tcMethods.
-}

tcSpecInstPrags :: DFunId -> InstBindings GhcRn
                -> TcM ([LTcSpecPrag], TcPragEnv)
tcSpecInstPrags :: Id -> InstBindings GhcRn -> TcM ([LTcSpecPrag], TcPragEnv)
tcSpecInstPrags Id
dfun_id (InstBindings { ib_binds :: forall a. InstBindings a -> LHsBinds a
ib_binds = LHsBinds GhcRn
binds, ib_pragmas :: forall a. InstBindings a -> [LSig a]
ib_pragmas = [LSig GhcRn]
uprags })
  = do { spec_inst_prags <- (GenLocated SrcSpanAnnA (Sig GhcRn)
 -> IOEnv (Env TcGblEnv TcLclEnv) LTcSpecPrag)
-> [GenLocated SrcSpanAnnA (Sig GhcRn)] -> TcM [LTcSpecPrag]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM ((Sig GhcRn -> TcM TcSpecPrag)
-> GenLocated SrcSpanAnnA (Sig GhcRn)
-> IOEnv (Env TcGblEnv TcLclEnv) LTcSpecPrag
forall t a b.
HasLoc t =>
(a -> TcM b) -> GenLocated t a -> TcM (Located b)
wrapLocM (Id -> Sig GhcRn -> TcM TcSpecPrag
tcSpecInst Id
dfun_id)) ([GenLocated SrcSpanAnnA (Sig GhcRn)] -> TcM [LTcSpecPrag])
-> [GenLocated SrcSpanAnnA (Sig GhcRn)] -> TcM [LTcSpecPrag]
forall a b. (a -> b) -> a -> b
$
                            (GenLocated SrcSpanAnnA (Sig GhcRn) -> Bool)
-> [GenLocated SrcSpanAnnA (Sig GhcRn)]
-> [GenLocated SrcSpanAnnA (Sig GhcRn)]
forall a. (a -> Bool) -> [a] -> [a]
filter LSig GhcRn -> Bool
GenLocated SrcSpanAnnA (Sig GhcRn) -> Bool
forall p. UnXRec p => LSig p -> Bool
isSpecInstLSig [LSig GhcRn]
[GenLocated SrcSpanAnnA (Sig GhcRn)]
uprags
             -- The filter removes the pragmas for methods
       ; return (spec_inst_prags, mkPragEnv uprags binds) }

------------------------------
tcSpecInst :: Id -> Sig GhcRn -> TcM TcSpecPrag
tcSpecInst :: Id -> Sig GhcRn -> TcM TcSpecPrag
tcSpecInst Id
dfun_id prag :: Sig GhcRn
prag@(SpecInstSig XSpecInstSig GhcRn
_ LHsSigType GhcRn
hs_ty)
  = ErrCtxtMsg -> TcM TcSpecPrag -> TcM TcSpecPrag
forall a. ErrCtxtMsg -> TcM a -> TcM a
addErrCtxt (Sig GhcRn -> ErrCtxtMsg
SpecPragmaCtxt Sig GhcRn
prag) (TcM TcSpecPrag -> TcM TcSpecPrag)
-> TcM TcSpecPrag -> TcM TcSpecPrag
forall a b. (a -> b) -> a -> b
$
    do  { spec_dfun_ty <- UserTypeCtxt -> LHsSigType GhcRn -> TcM Type
tcHsClsInstType UserTypeCtxt
SpecInstCtxt LHsSigType GhcRn
hs_ty
        ; co_fn <- tcSpecWrapper SpecInstCtxt (idType dfun_id) spec_dfun_ty
        ; return (SpecPrag dfun_id co_fn defaultInlinePragma) }

tcSpecInst Id
_  Sig GhcRn
_ = String -> TcM TcSpecPrag
forall a. HasCallStack => String -> a
panic String
"tcSpecInst"

{-
************************************************************************
*                                                                      *
\subsection{Error messages}
*                                                                      *
************************************************************************
-}

instDeclCtxt1 :: LHsSigType GhcRn -> ErrCtxtMsg
instDeclCtxt1 :: LHsSigType GhcRn -> ErrCtxtMsg
instDeclCtxt1 LHsSigType GhcRn
hs_inst_ty
  = Either (LHsKind GhcRn) Type -> ErrCtxtMsg
InstDeclErrCtxt (Either (LHsKind GhcRn) Type -> ErrCtxtMsg)
-> Either (LHsKind GhcRn) Type -> ErrCtxtMsg
forall a b. (a -> b) -> a -> b
$ LHsKind GhcRn -> Either (LHsKind GhcRn) Type
forall a b. a -> Either a b
Left (LHsKind GhcRn -> Either (LHsKind GhcRn) Type)
-> LHsKind GhcRn -> Either (LHsKind GhcRn) Type
forall a b. (a -> b) -> a -> b
$ LHsSigType GhcRn -> LHsKind GhcRn
forall (p :: Pass). LHsSigType (GhcPass p) -> LHsType (GhcPass p)
getLHsInstDeclHead LHsSigType GhcRn
hs_inst_ty

instDeclCtxt2 :: Type -> ErrCtxtMsg
instDeclCtxt2 :: Type -> ErrCtxtMsg
instDeclCtxt2 Type
dfun_ty
  = Either (LHsKind GhcRn) Type -> ErrCtxtMsg
InstDeclErrCtxt (Either (LHsKind GhcRn) Type -> ErrCtxtMsg)
-> Either (LHsKind GhcRn) Type -> ErrCtxtMsg
forall a b. (a -> b) -> a -> b
$ Type -> Either (LHsKind GhcRn) Type
forall a b. b -> Either a b
Right (Type -> Either (LHsKind GhcRn) Type)
-> Type -> Either (LHsKind GhcRn) Type
forall a b. (a -> b) -> a -> b
$ Type
head_ty
  where
    ([Id]
_,[Type]
_,Type
head_ty) = Type -> ([Id], [Type], Type)
tcSplitQuantPredTy Type
dfun_ty