Migration guide for multiple home units

[Erdi, Gergo]

PUBLIC

Hi,

Is there a migration guide for GHC API clients for the new "multiple home units" feature?

In particular, I have the following two functions in my code that used to interact with related features of GHC:

addUnit :: UnitInfo -> HscEnv -> HscEnv
addUnit unitInfo at GenericUnitInfo{..}<mailto:unitInfo at GenericUnitInfo%7b..%7d> = modifyUnitState $ \us -> us
    { packageNameMap = addToUFM (packageNameMap us) unitPackageName unitId
    , unitInfoMap = M.insert unitId unitInfo $ unitInfoMap us
    }

registerModule :: (GhcMonad m) => ModDetails -> ModIface -> m ()
registerModule details iface = modifySession $ extendHpt . addModule
  where
    hmi = HomeModInfo iface details Nothing

    mod = mi_module iface
    modOrig = ModOrigin (Just True) [] [] True

    addModule = modifyUnitState $ \us -> us
        { moduleNameProvidersMap = M.insert (moduleName mod) (M.singleton mod modOrig) $ moduleNameProvidersMap us
        }

    extendHpt env = env
        { hsc_unit_env = let ue = hsc_unit_env env in ue
            { ue_hpt = addHomeModInfoToHpt hmi (hsc_HPT env)
            }
        }

I implemented these using the following utility function:

modifyUnitState :: (UnitState -> UnitState) -> HscEnv -> HscEnv
modifyUnitState f env = env
    { hsc_unit_env = let ue = hsc_unit_env env in ue
        { ue_units = f (ue_units ue)
        }
    }

With the recent changes to GHC, `modifyUnitState` doesn't work anymore because there is no single `UnitEnv` in the `HscEnv`. I tried updating the `HomeUnitEnv` of the current unit:

modifyUnitState :: (UnitState -> UnitState) -> HscEnv -> HscEnv
modifyUnitState f env = env
    { hsc_unit_env = let ue = hsc_unit_env env in
            ue_updateHomeUnitEnv f' (ue_currentUnit ue) ue
    }
  where
    f' hue = let units = homeUnitEnv_units hue in hue
        { homeUnitEnv_units = f units
        }

but this leads to a panic:

  GHC version 9.5.20220613:
        Unit unknown to the internal unit environment

unit (cortex-prim)
pprInternalUnitMap
  main (flags: main, Just main) ->
Call stack:
    CallStack (from HasCallStack):
      callStackDoc, called at compiler/GHC/Utils/Panic.hs:182:37 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Utils.Panic
      pprPanic, called at compiler/GHC/Unit/Env.hs:450:14 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Unit.Env
      ue_findHomeUnitEnv, called at compiler/GHC/Unit/Env.hs:394:48 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Unit.Env
      ue_unitFlags, called at compiler/GHC/Driver/Env.hs:421:18 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Driver.Env
      hscSetActiveUnitId, called at compiler/GHC/Driver/Env.hs:416:34 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Driver.Env
      hscSetActiveHomeUnit, called at compiler/GHC/Driver/Make.hs:1853:15 in ghc-lib-0.20220613-HQTH0nHhxeOCnJy5jYkZiX:GHC.Driver.Make


What is the new way of registering a new unit or new module with GHC?

Thanks,
            Gergo

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