Support cabal projects

[Fresheyeball]

This is a very nice tool, and I wish I could use it without stack.

[ndmitchell]

What's the reason for wanting to avoid stack? A simple stack init && weeder should be enough, so you don't have to use stack for day to day development - I don't.

If you do want to use Cabal, that's possible, but requires passing some extra flags to Cabal, then modifying Weeder to find the suitable output files. If there was a volunteer to do that I can give a few pointers.

[Fresheyeball]

I just don't use stack, since I manage haskell dependencies with nix. Can you tell me more about the output files?

[ndmitchell]

Ah, that makes a lot more sense. To a first approximation weeder needs to find the list of cabal files (easy if you aren't using stack), and from there find all the -dump-hi output files, which Stack generates as standard (hence why Stack makes it a lot easier). The options are to compile for Cabal/Nix using -dump-hi, or convert the .hi files after-the-fact. I don't know which one is easier, but happy with either approach.

[robcohen]

I also would like to use nix/cabal with weeder. The CI setup I have does not rely on stack, so that's not an option. If I can figure out how to do this, I'll do my best to submit a patch. If you know of any resources that document how I might do this, please let me know.

[robcohen]

Is it possible you meant "-ddump-hi" as documented here?

[ndmitchell]

Yep, I definitely meant -ddump-hi!

If you want to integrate it the file to replace/augment is https://github.com/ndmitchell/weeder/blob/master/src/Weeder.hs#L37-L42 which calls things in https://github.com/ndmitchell/weeder/blob/master/src/Stack.hs. Basically find the project, make sure it has .hi files and then get its necessary info.

[robcohen]

Thanks a lot, I appreciate the guidance!

[cleverca22]

mkDerivation = args: super.mkDerivation (args // {
  configureFlags = (args.configureFlags or []) ++ [ "--ghc-options=-ddump-hi" ];
});

if you put this inside your haskell package overrides, it will modify the configureFlags that get passed to cabal, and then you will probably have dump-hi files in every output path

[ndmitchell]

If you demand that anyone who has built with Cabal must have already passed ddump-hi then it probably isn't too hard a problem to solve - just rewriting things to look for cabal files and find hi files in a different place. Ideally in that case it would automatically figure out stack vs Cabal (perhaps with a setting to force one mode or the other).

[cleverca22]

input-output-hk/cardano-sl#3400
this restructures the file to have multiple haskell overlays, and then an optional overlay that does cabal configure --ghc-options=-ddump-hi for the entire set of haskell packages

[Shimuuar]

So what I found about generating *.dump-hi files using cabal new-build.

1. One needs to pass both -ddump-hi and -ddump-to-file to GHC. This could be done either using cabal new-build --ghc-option=-ddump-hi --ghc-option=-ddump-to-file ... invocation or using nix overrides.

2. All *.dump-hi files are located inside dist-newstyle even if project contains multiple packages

3. cabal doesn't clean up dist-newstyle so it may contain files from older builds. For example if one bumps version in cabal file and rebuilds. dist-newstyle will contain files from both old and new version

[ndmitchell]

Weeder 2.0 is being developed at https://github.com/ocharles/weeder so I suggest you go see if that fixes your issues.