Cabal: Feature request: absolute paths in ghc errors

Created on 7 Apr 2020 · 8Comments · Source: haskell/cabal

ghc will report errors and warnings in files relative to the hs-source-dirs that is declared in the .cabal file. This typically results in minimal output relative to the location of the .cabal file.

However, there are many workflows where this can result in problems, especially if the user invokes cabal build from a different directory which is common in multi-project builds.

It would be good if there was a cabal.project{.local} option made available that caused cabal to construct the absolute path of hs-source-dirs prior to invoking ghc.

Source

symbiont-sam-halliday

All 8 comments

This is a perfect issue to solve after https://github.com/haskell/cabal/issues/6667. Before that I'm not brave enough to change anything related to paths.

phadej on 7 Apr 2020

😄1

You might be interrested in my PR #6196 which addresses this issue using Entering/Leaving messages mentioning the directory Cabal is being invoked in, similar to how recursive Make deals with this problem.

DanielG on 7 Apr 2020

👍1

@DanielG thanks! That looks interesting. I think it'd be a lot cleaner generally if more things used absolute paths. Parsing contextual information seems like it might be impossible for many tools, e.g. a terminal that is just doing filename detection and linking.

symbiont-sam-halliday on 8 Apr 2020

@phadej if I wanted to make just this one directory absolute, do you know which line of code I should change? It's the only one I care about since it impacts ghc error messages.

symbiont-sam-halliday on 11 Sep 2020

I'm also interested in this feature. I also noticed https://gitlab.haskell.org/ghc/ghc/-/issues/15680

jacereda on 22 Sep 2020

❤1

Emacs 27.1 also has compilation-transform-file-match-alist that can serve as a workaround sometimes.

jacereda on 22 Sep 2020

It seems bizarre to me that stack implemented this as a post-processor of the ghc output, instead of just making the directory absolute before invoking ghc. As a proof of concept that this is all that is needed, I manually converted all my source locations to absolute paths and ghc did what I wanted. Of course, I can't commit that kind of change to my project's repo.

symbiont-sam-halliday on 23 Sep 2020

Is it possible that MAX_PATH restrictions on Windows had a role to play in keeping relative directories in stack?