Using GHC API with multiple targets

Sun Feb 19 12:57:47 UTC 2023

Hi Matt et al.!

Just to close the circle on this (I meant to post this several days ago), the error ended up being the fact that getCoreFS also made a call to runGhc, effectively creating a new environment with new session flags that needed to be set (duh). I'm still puzzling over the nuances of the many available DynFlags knobs and buttons, but no longer stuck on the errors I was getting.

Sincerely,

Bob

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------- Original Message -------
On Tuesday, February 14th, 2023 at 7:04 AM, Matthew Pickering <matthewtpickering at gmail.com> wrote:

> The GHC API code you give is fine, and works correctly. In the whole
> reproducer there is some additional code `getCoreFS` which is where
> the error comes from.
> 
> On Mon, Feb 6, 2023 at 1:56 PM Matthew Pickering
> matthewtpickering at gmail.com wrote:
> 
> > Can you put the whole example into a github repo and then I will look
> > at what is wrong?
> > 
> > Matt
> > 
> > On Mon, Feb 6, 2023 at 1:34 PM Eternal Recursion via ghc-devs
> > ghc-devs at haskell.org wrote:
> > 
> > > Thanks, Andreas!
> > > 
> > > I will check out the hint package and also play with verbosity and workingDirectory.
> > > 
> > > I considered using the Cabal library to derive the inputs from the project's cabal file, but it does help first to know what the needful inputs are, and where to stash them in the DynFlags session settings.
> > > 
> > > It's got to be one of those "One Weird Trick (tm)" gotcha settings that make it suddenly work. It seems obvious what some of the settings mean, but I suppose with more familiarity will come appreciation of nuances that make the apparently obvious meaning seem obviously wrong.
> > > 
> > > Sincerely,
> > > 
> > > Bob
> > > 
> > > Sent with Proton Mail secure email.
> > > 
> > > ------- Original Message -------
> > > On Monday, February 6th, 2023 at 7:53 AM, Andreas Klebinger klebinger.andreas at gmx.at wrote:
> > > 
> > > I think this is an ok forum for this kind of question. You could also try the haskell mailing list but I'm not sure if you will get more
> > > help tehre.
> > > 
> > > I recently played around with the ghc api and I found the `hint` package to be quite helpful as an example on how to do various
> > > things when using the ghc api to implement your own interpreter.
> > > 
> > > Have you tried setting verbose? Perhaps the include dir is relative to the working directory. In that case setting:
> > > 
> > > , workingDirectory = Just targetDir
> > > , importPaths = [targetDir] ++ importPaths dynflags
> > > 
> > > would mean ghc will search in targetDir/targetDir for Lib/Lib2. Should be easy to say for sure by enabling verbosity and looking at the output.
> > > 
> > > Am 06/02/2023 um 13:42 schrieb Eternal Recursion via ghc-devs:
> > > 
> > > If this is the wrong forum for this question (which as I think about it, I suppose it is) then redirection to a more appropriate mailing list or forum (or any advice, really) would be appreciated. I just figured this would be the forum with the best understanding of how the GHC API works (and has changed over time), and my longer term goal is indeed to contribute to it after I get past my learning curve.
> > > 
> > > Sincerely,
> > > 
> > > Bob
> > > 
> > > Sent with Proton Mail secure email.
> > > 
> > > ------- Original Message -------
> > > On Saturday, February 4th, 2023 at 4:04 PM, Eternal Recursion via ghc-devs ghc-devs at haskell.org wrote:
> > > 
> > > Hi Everyone!
> > > 
> > > I'm new here, trying to learn the GHC API. using 944 with cabal 3.8.1.0.
> > > 
> > > How do I correctly set a GHC Session's DynFlags (and/or other properties) to ensure local libraries imported by the main target are resolved properly at compile time?
> > > 
> > > What flags need to be set so that GHC is able to load/analyze/compile all relevant Libraries in a package?
> > > 
> > > This is my current code:
> > > 
> > > withPath :: FilePath -> IO ()
> > > withPath target = do
> > > let targetDir = takeDirectory target
> > > let targetFile = takeFileName target
> > > listing <- listDirectory targetDir
> > > let imports = filter (\f -> takeExtension f == ".hs") listing
> > > print imports
> > > let moduleName = mkModuleName targetFile
> > > g <- defaultErrorHandler defaultFatalMessager defaultFlushOut
> > > $ runGhc (Just libdir) $ do
> > > initGhcMonad (Just libdir)
> > > dynflags <- getSessionDynFlags
> > > setSessionDynFlags $ dynflags { ghcLink = LinkInMemory
> > > , ghcMode = CompManager
> > > , backend = Interpreter
> > > , mainModuleNameIs = moduleName
> > > , workingDirectory = Just targetDir
> > > , importPaths = [targetDir] ++ importPaths dynflags
> > > }
> > > targets <- mapM (\t -> guessTarget t Nothing Nothing) imports
> > > setTargets targets
> > > setContext [ IIDecl $ simpleImportDecl (mkModuleName "Prelude") ]
> > > load LoadAllTargets
> > > liftIO . print . ppr =<< getTargets
> > > getModuleGraph
> > > putStrLn "Here we go!"
> > > print $ ppr $ mgModSummaries g
> > > putStrLn "☝️ "
> > > 
> > > However, when I run it (passing to example/app/Main.hs, in which directory are Lib.hs and Lib2.hs, the latter being imported into Main), I get:
> > > 
> > > $ cabal run cli -- example/app/Main.hs
> > > Up to date
> > > ["Main.hs","Lib.hs","Lib2.hs"]
> > > [main:Main.hs, main:Lib.hs, main:Lib2.hs]
> > > Here we go!
> > > [ModSummary {
> > > ms_hs_hash = 23f9c4415bad851a1e36db9d813f34be
> > > ms_mod = Lib,
> > > unit = main
> > > ms_textual_imps = [(, Prelude)]
> > > ms_srcimps = []
> > > },
> > > ModSummary {
> > > ms_hs_hash = e1eccc23af49f3498a5a9566e63abefd
> > > ms_mod = Lib2,
> > > unit = main
> > > ms_textual_imps = [(, Prelude)]
> > > ms_srcimps = []
> > > },
> > > ModSummary {
> > > ms_hs_hash = 5f6751d7f0d5547a1bdf39af84f8c07f
> > > ms_mod = Main,
> > > unit = main
> > > ms_textual_imps = [(, Prelude), (, Lib2)]
> > > ms_srcimps = []
> > > }]
> > > ☝
> > > 
> > > example/app/Main.hs:4:1: error:
> > > Could not find module ‘Lib2’
> > > Use -v (or `:set -v` in ghci) to see a list of the files searched for.
> > > |
> > > 4 | import qualified Lib2 as L2
> > > | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > cli: example/app/Main.hs:4:1: error:
> > > Could not find module `Lib2' Use -v (or` :set -v` in ghci) to see a list of the files searched for.
> > > 
> > > What do I need to do differently to make this work?
> > > 
> > > I have a local Cabal file I could use, but to know what I need out of it, I need to understand the minimum required info to get this to work. TIA!
> > > 
> > > Sincerely,
> > > 
> > > Bob
> > > 
> > > Sent with Proton Mail secure email.
> > > 
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> > > 
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