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

1 Jul 2021

      PUBLIC

Unfortunately, that would take quite some extra effort. However, I think I have figured this out in the meantime: it seems it wasn't the FinderCache that needed invalidating, but the ModuleGraph. So now I have the following code for changing the home unit:

```
setHomeUnit :: (GhcMonad m) => UnitId -> m ()
setHomeUnit unitId = do
    modifySession $ \env -> env
        { hsc_dflags = (hsc_dflags env)
            { homeUnitId = unitId
            }
        }
    invalidateModSummaryCache

invalidateModSummaryCache :: (GhcMonad m) => m ()
invalidateModSummaryCache = modifySession $ \env -> env
    { hsc_mod_graph = invalidateMG (hsc_mod_graph env)
    }
  where
    invalidateMG = mapMG invalidateMS
    invalidateMS ms = ms{ ms_hs_date = addUTCTime (-1) (ms_hs_date ms) }
```

Here, `invalidateModSummaryCache` is based on the one in the `GHC` module which doesn't export it.

With the addition of `invalidateModSummaryCache` to `setHomeUnit`, I can now import `MyLib` from `Test` without using a package-qualified import. Adding or removing a `flushFinderCaches` call doesn’t seem to change anything.

-----Original Message-----
From: Matthew Pickering  
Sent: Wednesday, June 30, 2021 6:11 PM
To: Erdi, Gergo 
Subject: [External] Re: Loading a typechecked module and then using it immediately as a package

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Could you provide the code which is failing? Then it will be easier to fix.

On Tue, Jun 29, 2021 at 12:00 PM Erdi, Gergo  wrote:
...
PUBLIC
Should I? OK, I just tried calling `flushFinderCaches` after I change the home unit to `mainUnitId`, but I still get exactly the same behaviour: `findInstalledHomeModule` returns `InstalledFound` and things go downhill from there.
-----Original Message-----
From: Matthew Pickering 
Sent: Tuesday, June 29, 2021 6:34 PM
To: Erdi, Gergo 
Cc: ghc-devs@haskell.org
Subject: [External] Re: Loading a typechecked module and then using it immediately as a package
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Are you clearing the FinderCache?
On Tue, Jun 29, 2021 at 11:14 AM Erdi, Gergo  wrote:
...
PUBLIC
I don't know yet what's going on, but one thing I did notice is that `findInstalledHomeModule` returns `InstalledFound` for `MyLib`, which doesn't sound right to me -- `MyLib` should come from the "fake-uid" unit, and `Test` is typechecked in the `mainUnitId`.
-----Original Message-----
From: Erdi, Gergo
Sent: Tuesday, June 29, 2021 5:51 PM
To: Matthew Pickering 
Subject: Re: Loading a typechecked module and then using it immediately as a package
PUBLIC
I tried moving `MyLib.hs` into a directory different than `Test.sh`, but the error message still refers to its correct location! So this error is not guessing the file name of where `MyLib.hs` could be loaded from; instead, it seems to refer correctly to where the module (previously loaded) was. Hmm.
-----Original Message-----
From: Matthew Pickering 
Sent: Tuesday, June 29, 2021 5:04 PM
To: Erdi, Gergo 
Subject: [External] Re: Loading a typechecked module and then using it immediately as a package
Do you have a `MyLib.hs` source file? If you move that somewhere else (another folder) then things might work?
On Tue, Jun 29, 2021 at 9:41 AM Erdi, Gergo  wrote:
...
PUBLIC
What's weird about it is that if I print the `moduleNameProvidersMap`, I can see `MyLib` inside, and it looks no different than any other module from e.g. `ghc-prim` that I can import into `Test.hs` without any package qualification. Also, why does the error message refer to the file name `input/MyLib.hs`? Why does GHC even know that that is where it would have to be loaded from, if it weren't to be used from an already loaded package?
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