-Werror is inconvenient for local builds

[robrix]

My goal with enabling -Werror in cabal.project for local builds was to make it harder to run into cases where the build passes locally but fails in CI because e.g. you’ve got warnings in some file that you haven’t touched recently and so you don’t see them. In practice, it’s just become a pain for any workflow using cabal build instead of e.g. script/repl, often necessary to e.g. iterate on haskell-tree-sitter stuff.

Thus, I kinda think we should remove the setting in cabal.project and only enable it in CI builds.

[robrix]

(This was biting @tclem the other day.)

[patrickt]

I use cabal build a lot and would love this. I think we can just do it by adding --ghc-options=“-Werror” to our invocation of cabal configure in haskell.yml.

[robrix]

Well, this isn’t going to be as easy as I’d hoped—cabal uses --ghc-options flags passed on the CLI as options for the dependencies, and what do you know, some of them have warnings:

System/Random.hs:43:1: error: [-Wtabs, -Werror=tabs]
    Tab character found here, and in 74 further locations.
    Please use spaces instead.
   |
43 |         (
   | ^^^^^^^^