-Werror has unintended consequenses in a release. Say you are using transformers/mtl and you want to stay backwards compatible, you can't use Except since it's just in the new versions, but with -Werror you couldn't use Error since it would produce deprecation warnings. CPP isn't an option since that would change the implementation. I don't like the idea of disabling deprecation warninings since that setting has at least module level granularity, if other deprecations pop up I want to see those! By enabling -Werror you are turning a non breaking change (deprecation) into a breaking one and not even an upper bound of <= A.B.C.D would be safe since the number of components are arbitrary. The granularity of disabled warnings is part of the problem, it'd be really nice if you could disable deprecation warnings for specific identifiers, same with a lot of the other warnings. - Adam On Tue, Jul 1, 2014 at 7:34 PM, Carter Schonwald

wrote:

yeah, -Wall makes enough noise to have a good ROI

What I do though, is enable Werror on my Travis Ci formulae.

On Tue, Jul 1, 2014 at 1:30 PM, Brandon Allbery wrote:

...

On Tue, Jul 1, 2014 at 1:25 PM, Johan Larson wrote:

...

Is there a consensus within the Haskell community on the use of -Werror in packages uploaded to Cabal?

GHC's interpretation of Haskell, and the warnings it provides, change often enough that -Werror is generally a good way to lock a package to one or a small number of GHC releases. As such, last I heard Hackage complained if -Werror was found in a package's cabal file.

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@Peter you'll want to write flag maintainer description: Enable settings for the package maintainer. default: False manual: True note the Manual : True piece, you'll be creating a world of sad if cabal-install auto sets that to true by accident ! :) On Tue, Jul 1, 2014 at 2:23 PM, Peter Jones wrote:

Johan Larson writes:

...

Is there a consensus within the Haskell community on the use of -Werror in packages uploaded to Cabal?

I like to hide -Werror behind a cabal flag:

flag maintainer description: Enable settings for the package maintainer. default: False

if flag(maintainer) ghc-options: -Werror

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every flag defaults to Manual: True I think and then when cabal is trying to find a good build plan it will twiddle flags! On Tue, Jul 1, 2014 at 3:06 PM, Peter Jones wrote:

Carter Schonwald writes:

...

note the Manual : True piece, you'll be creating a world of sad if cabal-install auto sets that to true by accident ! :)

How would that happen? (Just curious.)

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I meant defaults to manual : false, But you get the idea. (I could be wrong. But still worth being explicit in your cabal files so no need to remember what the default is) On Tuesday, July 1, 2014, Peter Jones wrote:

Carter Schonwald javascript:;> writes:

...

every flag defaults to Manual: True I think and then when cabal is trying to find a good build plan it will twiddle flags!

Wow. Well, that's good to know. Thanks.

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On Tue, Jul 1, 2014 at 9:20 PM, Ivan Lazar Miljenovic < ivan.miljenovic@gmail.com> wrote:

Why does cabal-install twiddle flags though?

Surely if I say "default: False" that means "don't set this to True unless you actually want it". Having an extra "Manual" field seems like duplication.

Not exactly. You use it to specify which alternative to try first; and the reason it's trying alternatives is so that it can adapt to different platforms: dependency versions (e.g. the old split-base flag), Unix vs. Windows, etc. Controlling which one is tried first may be necessary to ensure it doesn't accidentally match something that appears to work but is less correct or appropriate than the alternative. For example, using an older library setup may work in installations that have both old and new libraries, but trying the new one first is likely to have e.g. performance or compatibility benefits. -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net