Loading a typechecked module and then using it immediately as a package

[Matthew Pickering]

Hi Gergo,

Please see a minimal example in this gist.

https://gist.github.com/mpickering/5029c7f244c484c91d665bcbc6bc6406

Cheers,

Matt

On Fri, Jun 25, 2021 at 10:20 AM Erdi, Gergo via ghc-devs
<ghc-devs at haskell.org> wrote:
>
> PUBLIC
>
>
> Hi,
>
>
>
> I have the following to .hs files:
>
>
>
> MyLib.hs:
>
> module MyLib where
> …
>
> Test.hs:
>
> {-# LANGUAGE PackageImports  #-}
> module Test where
> import “my-pkg” MyLib
> …
>
>
>
> I would like to parse/typecheck/load MyLib.hs into some Unit “my-unit”, then add that to the package “my-pkg”, and then typecheck Test.hs, all in-proc using the GHC API, without putting any other files on disk. How do I do that?
>
>
>
> What I tried is loading MyLib.hs after setting the homeUnitId in the DynFlags to “my-unit”, then editing the packageNameMap in the unitState of the DynFlags to may “my-pkg” to “my-unit”:
>
> setHomeUnit :: (GhcMonad m) => UnitId -> m ()
>
> setHomeUnit unitId = do
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>     dflags <- getSessionDynFlags
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>     modifySession $ \h -> h{ hsc_dflags = dflags{ homeUnitId = unitId } }
>
>
>
> registerUnit :: (GhcMonad m) => PackageName -> UnitId -> m ()
>
> registerUnit pkg unitId = modifySession $ \h -> h{ hsc_dflags = addUnit $ hsc_dflags h }
>
>   where
>
>     addUnit dflags = dflags
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>         { unitState = let us = unitState dflags in us
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>             { packageNameMap = M.insert pkg (Indefinite unitId Nothing) $ packageNameMap us
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>             }
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>         }
>
>
>
> pipeline = do
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>         setHomeUnit myUnit
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>         loadModule =<< typecheckModule =<< parseModule =<< modSumarryFor “MyLib”
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>         registerUnit myPkg myUnit
>
>
>
>         setHomeUnit mainUnitId
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>         typecheckModule =<< parseModule =<< modSumarryFor “Test”
>
>
>
>
>
> Alas, this doesn’t work: the import of `MyLib` from `my-pkg` fails with:
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>
>
> input/linking/Test.hs:5:1: error:
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>     Could not find module ‘MyLib’
>
>     It is not a module in the current program, or in any known package.
>
>
>
> TBH I’m not very surprised that it didn’t work – that registerUnit function is doing some pretty deep surgery on the unitState that probably breaks several invariants. Still, I wasn’t able to find a better way – all the functions in GHC.Unit.State seem to be for querying only.
>
>
>
> Thanks,
>
>             Gergo
>
>
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