Migration guide for multiple home units

Matthew Pickering matthewtpickering at gmail.com
Thu Jun 16 14:54:45 UTC 2022


Hi Gergo

The error tells you what you only have setup the HscEnv so that
there's one unit called main, but you are attempting to compile
something with unit id cortex-prim.

Perhaps you could be inspired by `setSessionDynFlags` which deals with
renaming the main unit id if you are compiling a unit which have a
different unit id. (See setUnitDynFlagsNoCheck).

Matt


On Thu, Jun 16, 2022 at 5:01 AM Erdi, Gergo via ghc-devs
<ghc-devs at haskell.org> wrote:
>
> 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{..} = 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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