Expand arg locations

[sayrer]

This fixed #801 for me.

[hlopko]

Just a quick drive by - could you add a test?

[illicitonion]

Just a quick drive by - could you add a test?

An easy way to do this could be to generate in a genrule a file which sets a --cfg flag, and then pass @$(location :generated-file) as a rustc_flags value, and then assert in a main method that that cfg is set. Possibly this could conveniently live in https://github.com/bazelbuild/rules_rust/tree/main/examples/env_locations :)

[sayrer]

Just a quick drive by - could you add a test?

An easy way to do this could be to generate in a genrule a file which sets a --cfg flag, and then pass @$(location :generated-file) as a rustc_flags value, and then assert in a main method that that cfg is set. Possibly this could conveniently live in https://github.com/bazelbuild/rules_rust/tree/main/examples/env_locations :)

Oh... maybe you meant I should make a separate test file. Happy to do so if it matters.

[UebelAndre]

Oh... maybe you meant I should make a separate test file. Happy to do so if it matters.

I personally think it's better to add a small and focused use use of this functionality to the test module but I'll defer to @hlopko on this one.

Otherwise looks good to me! 😄

[illicitonion]

LGTM - thanks!

[hlopko]

Thank you so so much for a solid PR. Could you update docs of rule attributes that are affected by this PR to mention that macros are expanded?

[sayrer]

It looks to me like the only issues remaining here might be small documentation / test changes, although I think I've resolved all of the comments.

I don't feel strongly about any of them, so I'd suggest merging this and then changing any of those things in a follow-up, rather than leaving comments here. That will make it easier to work on a California vs. Munich schedule.

[hlopko]

Thank you so much! Looks great to me!