[Haskell-cafe] With cabal.project, what's the story about warning and -Werror compiler flags?

Mikolaj Konarski mikolaj at well-typed.com
Mon Aug 29 04:58:07 UTC 2022

Hi Nicolas,

> Before, I put compiler warning flags like `-Wall` in `Ghc-Options`
> ..
> Having these options in `mypackage.cabal` always felt slightly weird,
> since they are in no way required for a package to function: they're
> developer options, not user/consumer options.

They'd be certainly out of place in a binary package. However,
a source package is meant to be compiled, so instructing
the compiler to produce warnings during compilation seems relevant.
A related reason is that IIRC haskell-ci does `cabal sdist` and then
runs all its operations based on the resulting source package.
So, if you want to see warnings in CI logs, you need to retain
the relevant instruction in the source package created by `cabal sdist`.
And warnings sometimes help to explain why compilation fails
or why the resulting binary misbehaves.

> > If it is, I did run into a couple of issues getting things to actually
> > work. Whilst putting `Ghc-Options` in a `Package mypackage` section in
> > `cabal.project` seems to work, I'm unable to achieve the same resulsts
> > for C compiler invocations. Presumably there's a `Gcc-Options` setting
> > one can use (which is also generated in `cabal.project.local` by `cabal
> > configure --gcc-options ...`). However, in testing, it appears said
> > compiler optons are only passed to GCC when compiling, e.g., a HSC2HS
> > file, but not when compiling a C file part of a `C-Sources` setting
> > (whilst `Cc-Options` in `mypackage.cabal` are).
> >
> > Is there some discrepancy between what can be done from `cabal.project`
> > vs. `mypackage.cabal`? Is this intentional? Am I trying to accomplish
> > something that isn't/shouldn't be supported by Cabal in the first
> > place?

That sounds like a bug. Is there anything relevant in the issue tracker?

All the best,

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