commit c1274b689f9bdee0aa6a7fd0899deb246cd08031
author Damien DeVille <damien@ddeville.me> Thu Dec 09 11:59:00 2021 -0800
committer GitHub <noreply@github.com> Thu Dec 09 14:59:00 2021 -0500
tree 53828d2ab5b559bbf614d990f3b8bfac3a62119f
parent e50b151674ce6e2565d17ef15c016023a1356396

Support `cargo:rustc-link-arg=FLAG` in build script runner (#1061)

Cargo 1.50 added support for `cargo:rustc-link-arg` and `cargo:rust-link-arg-bins` instructions in build script output (`rustc-cdylib-link-arg` has been supported since 1.35 and `cargo:rustc-link-arg-bin` was later added in 1.54).

The build script runner currently prints a warning when `rustc-cdylib-link-arg` is used but entirely ignores the other ones (likely setting them as `BuildScriptOutput::DepEnv` since this is the default branch).

This patch adds support for the `cargo:rustc-link-arg` instruction and prints an warning when `cargo:rust-link-arg-bins` and `cargo:rust-link-arg-bin` are used, just like `rustc-cdylib-link-arg`.

Note that `cargo:rustc-link-arg` is important because `cargo` errors when `cargo:rustc-flags` is used for anything that isn't a `-l` or `-L` flag (nb: this is enforced by cargo so it'd work with Bazel). There are cases (such as linking a `-weak_framework` or `-weak_library` on macos) that cannot use `cargo:rustc-link-lib` and passing a custom `-Clink-arg` is required)

I think that we should also support `cargo:rust-link-arg-bins`, `rustc-cdylib-link-arg` and `cargo:rustc-link-arg-bin` but that's a bigger task since it requires knowing the crate type the build output will apply to. I've made issue https://github.com/bazelbuild/rules_rust/issues/1062 for it.

Ref: https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script