RFC: `fsyntax-only` as an alias for `fparse-only` in `f18`

Hi all,

Recently we've ported the preprocessor tests to use the new Flang driver[1]. Soon we will be ready to port OpenMP and OpenACC tests. As the new driver and `f18` use slightly different spellings for options [2], we will require some workarounds. In this RFC I'd like to ask you for your opinion on using `-fparse-only` and `-fsyntax-only`.

In [3] we introduce `-fsyntax-only` as an alias for `-fparse-only` in `f18`. This is sufficient for us to start porting more tests to the new Flang driver very soon. Also, in [3] we port all tests to use `-fsyntax-only` instead of `-fparse-only`. Otherwise, `-fparse-only` remains supported by `f18` and you can continue to use it.

Does the approach from [3] work for you or would you prefer a different solution? I'm happy to propose some alternatives if there's interest.

Thank you for reading!

-Andrzej

[1] https://reviews.llvm.org/D94805
[2] [flang-dev] RFC: new Flang driver options
[3] ⚙ D95784 [flang][f18] Replace `-fparse-only` with `-fsyntax-only`

+1 for -fsyntax-only, consistency with Clang is worth it.

An alias for a while seems reasonable, eventually we phase alternatives out.

~ Johannes

+1 from me also. Seems like an obvious good thing to ease the transition from old driver to new and the new spelling was already agreed in your previous RFC.

Thank you both! There was an additional suggestion on Slack to remove `-fparse-only` entirely, but I prefer to do it in 2 steps. If this is fine with you, could you please review and approve?

Btw, I've updated the patch to make it clear that `-fparse-only` is deprecated. Users will also see this warning:

warning: `-fparse-only` is deprecated and will be removed in the future, use `-fsyntax-only` instead

-Andrzej