Module paths with `/` as separator are broken in Windows

[keithfancher]

Discovered while working on this HLS PR: haskell/haskell-language-server#4023, related to these issues:

• Stan plugin recommends StrictData pragma even when it is in scope haskell/haskell-language-server#3174
• Stan should normalize incoming file paths to be relative stan#556

Stan, via extensions, appears to be prepending the hs-source-dirs from the .cabal file verbatim onto the module name. This means if the .cabal file uses / as its path separators, the returned file paths (and associated extension map) will be broken for Windows users.

For example, if your cabal file has:

  hs-source-dirs: extension-tests/language-pragma

... then the resulting Map key winds up looking like this for Windows users:

extension-tests/language-pragma\\LanguagePragmaTest.hs

This results in Map lookups missing, which in turn results in Stan not recognizing any of a project's enabled extensions. (One of the causes for the above-mentioned HLS issue.)

From a quick look, I think the issue might be happening around here somewhere. (I do see some Cabal version checks, not sure how those play into this...)

[tomjaguarpaw]

Thanks for the report. stan and extensions have very little active maintainership currently. I'm happy to oversee and advise a patch to fix this, but I won't have time to do it myself any time in the near future. Perhaps @0rphee is interested?

[tomjaguarpaw]

The first thing to do would be to produce an example that demonstrates the current behaviour, as simply as possible.

[0rphee]

Probably I won't be able to work on this for the foreseeable future, maybe in a few months.. :)