Specifying `--profile` and `--release` when running `cargo rustc` doesn't work anymore

[koute]

Problem
This used to work:

cargo rustc --lib --profile test --release

Now it doesn't:

$ cargo rustc --lib --profile test --release
error: Conflicting usage of --profile and --release

How am I supposed to compile unit tests in release mode through cargo rustc now? I can use --tests, but that will also compile integration tests (which I don't want), and --test $crate_name doesn't work.

Steps

1. cargo new --lib foobar
2. cd foobar
3. cargo rustc --lib --profile test --release

Notes

Version which worked: cargo 1.39.0-nightly (3596cb86b 2019-09-19) (and all of the previous versions)
Version which doesn't work: cargo 1.40.0-nightly (8b0561d68 2019-09-30)

This is a regression from stable to nightly.

[koute]

cc @da-x

[da-x]

@koute - sorry for the regression. Queued up a fix.

[koute]

Thanks!

It's nice to see that cargo's handling of profiles is getting cleaned up. However, this definitely needs a deprecation warning so that whoever depends on the current behavior could migrate, and it'd also be great if we made sure that there is no loss of functionality (e.g. the case where I want to compile only the unit tests in release mode, which as far as I can see after your changes becomes impossible?).

[da-x]

@koute. Yes, this was discussed when implementing the PR for the RFC. We may need to gather up these use cases and have special flags for them, or do something else.