Allow passing RTS options to GHC in stack.yaml

[parsonsmatt]

Note: Documentation fixes for https://docs.haskellstack.org/en/stable/ should target the "stable" branch, not master.

Please include the following checklist in your PR:

• Any changes that could be relevant to users have been recorded in the ChangeLog.md
• The documentation has been updated, if necessary.

I added an integration test that ensures stack builds successfully when passing RTS options to GHC.

Fixes #5180

[parsonsmatt]

it seems like the integration tests on Mac are broken for an unrelated reason - failing to execute GHC for permissions?

[snoyberg]

I'm not sure how important this is in this case, but this has quadratic performance. I'd recommend instead collecting a list of Texts and then combining with T.unwords. In fact, I think then you'd be able to use break (== "-RTS")

[parsonsmatt]

Thanks for the tip! I've provided a much nicer looking implementation, and it even made me aware of the case where a user does not provide a -RTS in the argument list.

I decided to splice a -RTS on the end of the collected RTS args regardless. This matches the syntax you might use in a CLI invocation - ghc --version +RTS -N -A128m. As far as I know, this shouldn't cause any problems - any string without an -RTS would completely fail without this, and any string with non-RTS arguments after a +RTS would fail in either case.

[snoyberg]

LGTM, thanks!