GHC case change for warning breaks haskell-mode check

[sirlensalot]

As of 8.0.2, GHC is now issuing warnings with a lower-case 'w':

src/Pact/Compile.hs:49:1-40: warning: [-Wunused-imports] …
    The import of ‘Hash’ from module ‘Pact.Types.Crypto’ is redundant

As a result, tools are not recognizing this and flagging things as errors or worse. Here's relevant results from a grep:

./haskell-interactive-mode.el:1032:             (not (string-match "^\n<interactive>:[-0-9]+:[-0-9]+:[\n ]+Warning:" response)))
./haskell-load.el:204:        ((string-match "Warning: orphan instance: " msg)
./haskell-load.el:398:    ((string-prefix-p "Warning:\n    " haskell-msg)
./haskell-load.el:521:             (type (cond ((string-match "^Warning:" error-msg)  'warning)

For string-match, using [Ww]fixes the issue and is presumably backward-compatible. Ie for line 521:

             (type (cond ((string-match "^[Ww]arning:" error-msg)  'warning)

works with my GHC 8.0.2 environment. string-prefix-p would need a better fix. I can't comment on the other places string-match is in use so I would request someone more familiar with this codebase make the fix.

NB: Why in [deity]'s name did they change the case in 8.0.2????? Do the haskell gods just enjoy breaking tools, because the GHC8 upgrade wasn't painful enough???

[ivan-m]

This seems to be the commit they did it in (or at least some of their test-cases started to use the lower-case variant).

[gracjan]

Gods are whimsical and erratic and we were almost prepared: #1168.

[sirlensalot]

Deeper research using a grep for "arning" in *.el files. Relevant finds:

1. ./haskell-compile.el:73: ":\\(?6:\n?[ \t]+[Ww]arning:\\)?") From Improve warning recognition. Clean up whitespace. #1477, which was aware of the case issue. not sure if it works with [-Wfoo] stuff that shows up though.
2. ./haskell-interactive-mode.el:1032: (not (string-match "^\n<interactive>:[-0-9]+:[-0-9]+:[\n ]+Warning:" response))) This is a hard one to test as it's unclear why it's avoiding warnings; in my REPL errors are getting clobbered with weird types no matter what. Nonetheless, would seem to be safe to change to [Ww].
3. ./haskell-load.el:204: ((string-match "Warning: orphan instance: " msg) This is broken irrespective of case change.
4. ./haskell-load.el:398: ((string-prefix-p "Warning:\n " haskell-msg) Also broken irr. of case change
5. ./haskell-load.el:521: (type (cond ((string-match "^Warning:" error-msg) 'warning) this is the main one for this issue, easily fixed with [Ww]
6. ./inf-haskell.el:84: ("^\\(.+?\\):\\([0-9]+\\):\\(\\([0-9]+\\):\\)?\\( \\|\n *\\)\\([Ww]arning\\)?" case is fine, again not sure it handles [-Wfoo] stuff.

Proposal: I go ahead and introduce [Ww] for 2-5, but will only test the results for 5, and assume it doesn't break things further for the other cases. Please LMK if this is acceptable.

[gracjan]

Yes, good enough! Go ahead!