A 'ModuleGraph' contains all the nodes from the home package (only). See 'ModuleGraphNode' for information about the nodes.

Modules need to be compiled. hs-boots need to be typechecked before the associated "real" module so modules with {-# SOURCE #-} imports can be built. Instantiations also need to be typechecked to ensure that the module fits the signature. Substantiation typechecking is roughly comparable to the check that the module and its hs-boot agree.

The graph is not necessarily stored in topologically-sorted order. Use topSortModuleGraph and flattenSCC to achieve this.

Why do we ever need to construct empty graphs? Is it because of one shot mode?

Construct a module graph. This function should be the only entry point for building a ModuleGraph, since it is supposed to be built once and never modified.

If you ever find the need to build a ModuleGraph iteratively, don't add insert and update functions to the API since they become footguns. Instead, design an API that allows iterative construction without posterior modification, perhaps like what is done for building arrays from mutable arrays.

A 'ModuleGraphNode' is a node in the 'ModuleGraph'. Edges between nodes mark dependencies arising from module imports and dependencies arising from backpack instantiations.

Collect the immediate dependencies of a ModuleGraphNode, optionally avoiding hs-boot dependencies. If the drop_hs_boot_nodes flag is False, and if this is a .hs and there is an equivalent .hs-boot, add a link from the former to the latter. This has the effect of detecting bogus cases where the .hs-boot depends on the .hs, by introducing a cycle. Additionally, it ensures that we will always process the .hs-boot before the .hs, and so the HomePackageTable will always have the most up to date information.

Returns the number of nodes in a ModuleGraph

Map a function f over all the ModSummaries. To preserve invariants, f can't change the isBoot status.

Map a function f over all the ModSummaries, in IO. To preserve invariants, f can't change the isBoot status.

Look up a ModSummary in the ModuleGraph Looks up the non-boot ModSummary Linear in the size of the module graph

Return all nodes reachable from the given NodeKey.

Reachability Query.

mgQuery(g, a, b) asks: Can we reach b from a in graph g?

Both a and b must be in g.

Many roots reachability Query.

mgQuery(g, roots, b) asks: Can we reach b from any of the roots in graph g?

Node b must be in g.

Turn a list of graph nodes into an efficient queriable graph. The first boolean parameter indicates whether nodes corresponding to hs-boot files should be collapsed into their relevant hs nodes.

This function returns all the modules belonging to the home-unit that can be reached by following the given dependencies. Additionally, if both the boot module and the non-boot module can be reached, it only returns the non-boot one.

This function filters out all the instantiation nodes from each SCC of a topological sort. Use this with care, as the resulting "strongly connected components" may not really be strongly connected in a direct way, as instantiations have been removed. It would probably be best to eliminate uses of this function where possible.