Please ensure cabal does not warn for incomplete-uni-patterns

[tomjaguarpaw]

As per this accepted GHC proposal, GHC will add incomplete-uni-patterns and incomplete-record-updates to -Wall. Could you please ensure that the following files do not give any warnings for incomplete-uni-patterns, perhaps by setting the pragma below? (A clean compile of cabal is needed to build GHC.)

{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}

• Cabal/Distribution/Backpack/Configure.hs
• Cabal/Distribution/Parsec.hs
• Cabal/Distribution/Simple/Build/Macros.hs
• Cabal/Distribution/Simple/GHC.hs
• Cabal/Distribution/Simple/GHCJS.hs
• Cabal/Distribution/Simple/UHC.hs
• Cabal/Distribution/Simple/Test/LibV09.hs
• Cabal/Distribution/Simple/BuildTarget.hs
• Cabal/Distribution/Simple/ShowBuildInfo.hs
• Cabal/Cabal/Distribution/Simple/Haddock.hs

[dwijnand]

When you say "Could you please ensure that the following files do not give any warnings" and then give a list specifying 1 particular file, I assume you found that file to have warnings. But I'm having a hard time reproducing that, after adding that pragma and running cabal build Cabal. Is there some step I'm missing?

[tomjaguarpaw]

I am currently implementing the above-mentioned proposal in GHC, i.e. that -Wincomplete-uni-patterns is added to -Wall. However, that file emits warnings under -Wincomplete-uni-patterns, breaking the build of GHC. I'm asking that -Wno-incomplete-uni-patterns is added on that file so that it will not break the build of GHC. Does that make sense?

[dwijnand]

If you have a look at https://travis-ci.com/dwijnand/cabal/builds/136806769 and the commit it builds from (which builds on current HEAD), and ignore the failures on older GHCs, you'll see that compilation didn't fail (and I believe warnings are set to fatal), so I do still need some information as to what Parsec.hs needs or how to get it to fail...

[tomjaguarpaw]

I'm saying that it will fail under -Wincomplete-uni-patterns and that warning will be included under -Wall under future GHCs, therefore Parsec.hs needs -Wno-incomplete-uni-patterns applied. In other words, what I'm asking you to do is exactly to merge dwijnand@4e6b2c5!

[dwijnand]

so I do still need some information

Thanks to @phadej I found out that the information I was missing is that the "no" in -Wno-incomplete-uni-patterns suppresses the warning. (I expanded on this in https://twitter.com/dwijnand/status/1195908792686391296.)

[tomjaguarpaw]

[Edited the list to include many more cases I found!]

[phadej]

Just out of curiosity, is there work on hadrian / shake to make them -Wincomplete-uni-patterns clean?
I opened to track that https://gitlab.haskell.org/ghc/ghc/issues/17577