compilation-mode in emacs no-longer creates links to files on errors/warnings

[wraithm]

Stack version

$ stack --version
Version 2.5.1, Git revision d6ab861544918185236cf826cb2028abb266d6d5 x86_64 hpack-0.33.0

Method of installation

• Official binary, downloaded from stackage.org or fpcomplete's package repository

Problem

Previous versions of stack printed errors in such a way that compilation-mode in emacs would detect the error and you could execute M-x first-error or similar function to go to the first error, and you can traverse the errors with M-x next-error and such. I think I actually also had to set --no-interleaved-output to get this to work well too in the previous version of stack I was on.

The new version of stack that I'm using breaks this. I think it's simply that the file paths are indented a bit. Emacs (and vim for quickfix afaict) use filepaths on newlines for detecting these errors. This is very frustrating that first-error, next-error, etc are broken.

Is it possible to use compilation-mode with stack in a simple way and get output such that emacs detects the errors?

[wraithm]

@snoyberg @mattaudesse @chrisdone Any thoughts here?

[mattaudesse]

Sorry @wraithm - I don't use this feature or know much about it.

[wraithm]

I think it's as simple as removing the indentation in the error output:

          indent = dropWhileEnd isSpace . unlines . fmap (\line -> "  " ++ line) . lines
          doubleIndent = indent . indent

https://github.com/commercialhaskell/stack/blob/master/src/Stack/Types/Build.hs#L216-L217

The file-name where the error occurs has to be at the beginning of the line for emacs or vim to detect it as an error.

This is a pretty serious usability bug, in my humble opinion. I've honestly been a lot slower at fixing code because of this! I imagine that there are some people silently suffering that vim quickfix and emacs compilation-mode aren't working properly.

[wraithm]

Okay, I built stack removing the indentation in Stack.Types.Build, and with --no-interleaved-output, compilation-mode started detecting errors again.

This issue is specific to having multiple packages in the same stack project. In a single package project, there is no extra indentation put in front of errors, and emacs/vim will detect the errors.