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

[Erdi, Gergo]

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 <matthewtpickering at gmail.com> 
Sent: Wednesday, June 30, 2021 6:11 PM
To: Erdi, Gergo <Gergo.Erdi at sc.com>
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 <Gergo.Erdi at sc.com> 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 <matthewtpickering at gmail.com>
> Sent: Tuesday, June 29, 2021 6:34 PM
> To: Erdi, Gergo <Gergo.Erdi at sc.com>
> Cc: ghc-devs at haskell.org
> Subject: [External] Re: Loading a typechecked module and then using it immediately as a package
>
> ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients.
>
>
> Are you clearing the FinderCache?
>
> On Tue, Jun 29, 2021 at 11:14 AM Erdi, Gergo <Gergo.Erdi at sc.com> 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 <matthewtpickering at gmail.com>
> > 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 <matthewtpickering at gmail.com>
> > Sent: Tuesday, June 29, 2021 5:04 PM
> > To: Erdi, Gergo <Gergo.Erdi at sc.com>
> > 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 <Gergo.Erdi at sc.com> 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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Where you have a Financial Markets relationship with Standard Chartered PLC, Standard Chartered Bank and their subsidiaries (the "Group"), information on the regulatory standards we adhere to and how it may affect you can be found in our Regulatory Compliance Statement at https: //www.sc.com/rcs/ and Regulatory Compliance Disclosures at http: //www.sc.com/rcs/fm

Insofar as this communication is not sent by the Global Research team and contains any market commentary, the market commentary has been prepared by the sales and/or trading desk of Standard Chartered Bank or its affiliate. It is not and does not constitute research material, independent research, recommendation or financial advice. Any market commentary is for information purpose only and shall not be relied on for any other purpose and is subject to the relevant disclaimers available at https: //www.sc.com/en/regulatory-disclosures/#market-disclaimer.

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