------- Original Message -------
On Saturday, February 4th, 2023 at 4:04 PM, Eternal Recursion via ghc-devs <ghc-devs@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

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