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Yet another warning auto-fixer for GHC compilations with the following properties:

• Build system independent - can work with anything that emits GHC to stdout.
• Does not try to compile or fully parse the HS file. It doesn't depend on any Haskell parsing library (see End note about this).
• Can show a unidiff of proposed changes (-d).
• Can fix in place (-f).
• It's very fast.

Also, it is very limited. Currently only fixes a single type of warning, but an annoying one about redundant imports:

src/Main.hs:34:1: Warning:
    The import of ‘forM_, forM’ from module ‘Control.Monad’ is redundant

If you fully trust the thing:

cabal clean
cabal build 2> warnings.txt
cat warnings.txt | autofix-ghc --fix

Support you saved the above warning to warnings.txt by redirecting cabal output somehow.

$ cat warnings.txt | autofix-ghc --fix

autofix-ghc can fix: src/Main.hs

You can see a diff:

$ cat warnings.txt | autofix-ghc --diff

autofix-ghc can fix: src/Lib/Git.hs
diff -urN src/Main.hs src/Main.hs
--- src/Main.hs
+++ src/Main.hs
@@ -31,7 +31,7 @@
   ) where
 
 ------------------------------------------------------------------------------------
-import           Control.Monad             (forM_, forM, when)
+import           Control.Monad             (when)
 import           Control.Lens.Operators    ((&))
 import           Control.Monad.IO.Class    (liftIO)
 import           Control.Monad.Catch       (MonadMask)

And you can fix it:

$ cat warnings.txt | autofix-ghc --fix

autofix-ghc fixed: src/Main.hs

I wrote this in a day for teaching myself attoparsec. If you find this useful and want to improve it, pull requests are welcomed.