Using GHC API with multiple targets

[Eternal Recursion]

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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