stack script should allow setting ghc-options

[mgsloan]

Currently, stack script only allows specifying arguments to the user's program, not to the ghc invocation. Should probably use --ghc-arg as described in https://downloads.haskell.org/~ghc/master/users-guide/runghc.html , rather than passing the arguments directly. I suggest adding the following:

• --ghc-options, which works just like the argument to build
• --ghc-arg, which allows passing it to just the script command's ghc invocation.

[danieledapo]

@mgsloan if nobody has taken this yet, I can work on it.

I'm not sure I understand what would be the difference between --ghc-options and --ghc-arg though. My understanding is:

• stack script --resolver lts-9.2 --ghc-options -threaded -v5 would be roughly equivalent to runghc -v5 foo;
• stack script --resolver lts-9.2 --ghc-arg -v5 foo would be roughly equivalent to runghc --ghc-arg -v5 foo.

but I'm not sure that's 100% right.

[mgsloan]

@d-dorazio Awesome! Sorry for the delay in getting back to you on clarification.

I've thought about this a bit more, and actually I don't think it makes sense to allow providing ghc options for use when building packages (this is what I intended --ghc-options to be). So, this means no need to make up a new flag name (--ghc-arg).

So I think a better design is to make --ghc-options get passed to the ghc invocation. So, stack script --resolver lts-9.2 --ghc-options "-threaded -v5" would do something like runghc --ghc-arg "-v5 foo";

[dbaynard]

Closing due to #3519