Specify a different target when running unit tests

[seanybaggins]

When working with bare metal embedded systems, it would be nice to be able to run unit tests on your host machine using cargo test and then deploy to the target device using cargo run. Currently, to build different targets between tests and regular builds, your only option is to explicitly use the --target flag when invoking cargo.

The purpose of this pull request is have different targets between cargo build and cargo test without the need for the --target flag.

This was achieved by changing the .cargo/config.toml options.

Closes #6784

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

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[seanybaggins]

Some things I am still not pleased with...

cargo build --tests
still uses the build.target profile instead of the build.test-target profile.

Open to ideas for the best way to get the context for the --tests flag within the CompileKind::from_requested_targets function.

[seanybaggins]

Perhaps a better way to implement this is just to use the cargo make tool...

[alexcrichton]

Thanks for the PR! We discussed this a bit at the last Cargo meeting, and we agree that this may not be the best way to implement it. Especially the gotchas you mention (cargo build --tests not using the same target) feels sort of weird. Would using a solution like cargo make work for you?

[seanybaggins]

Sorry for such a late reply.

Yes. I think the cargo-make tool solves the problem this pull request was trying to address.