Using GHC API with multiple targets

Mon Feb 6 13:18:11 UTC 2023

Tbh, the current code is a bit of a Frankenstein cobbled together from the dead limbs of online GHC API tutorials past. I think that line was the swollen appendix of something. :)

But I can confirm that commenting out that line does not help. I get exactly the same module graph output and error message.

I will add enhanced verbosity as Andreas suggests and see under what rocks it's looking for Lib2. I can't believe it can't find it. I mean, it's right there.

Looking at the module graph, I gather I should want to see the local modules Lib and Lib2 in the ms_srcimps list. The ms_textual_imps list appears to be just a list of what modules are listed in the imports statements.

I also note parenthetically that the Lib import line is commented out in Main.hs. When I add it, it seems to be resolving to the wrong Lib module (libiserve or something like that IIRC) and then complains the function I'm trying to call isn't exported by it.

Any background about DynFlags for context is appreciated. It seems a rather large construct that has seen some mission creep and redesign efforts over the years...

Sincerely,

Bob

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------- Original Message -------
On Monday, February 6th, 2023 at 7:59 AM, Matthew Pickering <matthewtpickering at gmail.com> wrote:

> Looks like it would work to me if you remove
> 
> `setContext [ IIDecl $ simpleImportDecl (mkModuleName "Prelude") ]`
> 
> Why do you have this line?
> 
> Matt
> 
> On Mon, Feb 6, 2023 at 12:54 PM 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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