Add support for interaction with stack ghci.

[johnwalker]

Add stack ghci support from #744. Also fix a defcustom typo in haskell-process-args-cabal-repl.

[gracjan]

Thanks.

[swsnr]

Mmh, it seems that haskell-process-cabal-build (e.g. C-c C-c) doesn't understand stack yet, does it?

[johnwalker]

Thats right. For now, look to the bottom of https://github.com/chrisdone/chrisdone-emacs/blob/master/config/haskell.el

I think thats the right approach for haskell-mode, too?

[peti]

Has anyone figured out a good way to switch easily between stack and cabal projects? (My emacs-fu is very weak, so it's quite possible that there's a simple and obvious solution that I'm unaware of). When I set haskell-process-type to auto, stack projects aren't recognized, unfortunately.

[srhb]

The only way I've found is to use a .dir-locals.el on an ad-hoc basis, which doesn't feel very nice. I'd settle for a menu when I start a haskell process, really.

[gracjan]

Starting a process already asks a lot of questions and we should strive to remove all of those.

[srhb]

I should have been more specific, because you're obviously right. It's a sane default to not ask too many questions. I guess I just want the option for a menu (because when you switch between cabal sandboxes, nix and stack, there's no good solution currently.)

[gracjan]

I think that the current 'auto' option has been irrevocably spoiled as there is no way to reliably detect cabal vs stack preference. Also note that nix can have all three possibilities: nix-ghci, nix-cabal and nix-stack, so it actually adds yet another dimension to the whole mix. I wonder if we somehow could get around the whole mess.

[peti]

Auto-detection cannot be 100% reliable, but IMHO it can be pretty good:

1. If the top-level directory relative to the current source module contains a stack.yaml file, then it's Stack.
2. If that directory contains a Cabal file and the directory layer above contains a stack.yaml file that mentions the Cabal file in its packages section, then it's Stack.
3. If there is a Cabal file but no Stack file, then it's Cabal.
4. If everything else fails, just load ghci.

[ivan-m]

@peti except that falls through in the case of "this project has stack support, but I don't want to use it" (e.g. cloned from upstream, but you're still using cabal), which is why I believe the current 'auto' option checks if there's stack.yaml and stack is in the PATH.