A UnitEnv provides the complete interface into everything that is loaded into a GHC session, including the HomeUnitGraph for mapping home units to their HomePackageTables (which store information about all home modules), and the ExternalPackageState which provides access to all external packages loaded.

This module is meant to be imported as UnitEnv when calling insertHpt:

import GHC.Unit.Env (UnitEnv, HomeUnitGraph, HomeUnitEnv)
import GHC.Unit.Env as UnitEnv

Here is an overview of how the UnitEnv, ModuleGraph, HUG, HPT, and EPS interact:

┌────────────────┐┌────────────────────┐┌───────────┐
│HomePackageTable││ExternalPackageState││ModuleGraph│
└┬───────────────┘└┬───────────────────┘└┬──────────┘
┌▽────────────┐    │                     │
│HomeUnitGraph│    │                     │
└┬────────────┘    │                     │
┌▽─────────────────▽┐                    │
│UnitEnv            │                    │
└┬──────────────────┘                    │
┌▽───────────────────────────────────────▽┐
│HscEnv                                   │
└─────────────────────────────────────────┘

The UnitEnv references both the HomeUnitGraph (with all the home unit modules) and the ExternalPackageState (information about all non-home/external units). The HscEnv references this UnitEnv and the ModuleGraph (which describes the relationship between the modules being compiled). The HomeUnitGraph has one HomePackageTable for every unit.

TODO: Arguably, the ModuleGraph should be part of UnitEnv rather than being in the HscEnv.

The hug prefix means the function returns only things found in home units.

This API is deprecated!