Re: Reconsidering -Wall and -Wcompat

Just as one data point, the Swift compiler is by default showing warnings about upcoming changes. Just like deprecation warnings, I do find that helpful. Based on that experience, including -Wcompat in -Wall seems like a good plan to me. Manuel

Ben Gamari :

tl;dr. GHC has a new set of warnings, -Wcompat, intended to give users advance notice of coming library changes. We want to know whether you think this set should be included in -Wall. See the Wiki [4] and voice your opinion via the linked poll.

Hello everyone,

GHC 8.0.1 will include a new warning group, -Wcompat, which arose out of the MonadFail proposal discussion [1] late last year. This warning set is intended to provide a means of informing users of coming changes in GHC's core libraries.

We would like to solicit the community's feedback on whether this new flag set should be implied by -Wall.

This proposal is motivated by concern expressed by some that -Wcompat would see little usage unless it is placed in one of the warning sets typically used during development. One such set is -Wall, which enables a generous fraction of GHC's warning collectionand is is intended [2] for use during development.

Unfortunately, despite the (albeit only recently stated) intent of flag, -Wall is widely used outside of development [3], often with the expectation that the result be warning-clean across multiple GHC versions. While we hope that -Wall will see less use in this context in the future, given its current role we wouldn't want to add options to it that would cause undue burden for users.

So, we are asking for your opinion: should -Wcompat be implied by -Wall? You can find a more thorough description of the precise proposal on the GHC Wiki [4]. It would be very much appreciated if you could take a few minutes familiarize yourself with the options and provide your thoughts via this quick poll,

https://docs.google.com/forms/d/1BmIQvhHcnDB79LgBvaWl_xXpS1q0dMHe3Gq9JeU9odM...

Feel free to discuss the issue further in this thread.

Thank you for sharing,

- Ben

[1] https://mail.haskell.org/pipermail/ghc-devs/2015-October/010101.html

[2] https://mail.haskell.org/pipermail/ghc-devs/2016-January/010955.html

[3] In a rather unscientific study, nearly half of packages on Hackage include it in ghc-options,

$ tar -xf ~/.cabal/packages/00-INDEX.tar $ (for pkg in $(ls); do ls $pkg/*/*.cabal | sort -r | head -n1; done) | xargs grep -L '\-Wall' | wc -l 4352 $ ls | wc -l 9347

[4] https://ghc.haskell.org/trac/ghc/wiki/Design/Warnings/Wcompat _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs