Tracking Issue for profile-hint-mostly-unused

[joshtriplett]

Summary

Implementation: #15643
Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#profile-hint-mostly-unused-option

This feature provides a new option in the [profile] section to enable the rustc hint-mostly-unused option. This is primarily useful to enable for specific dependencies:

[profile.dev.package.huge-mostly-unused-dependency]
hint-mostly-unused = true

To enable this feature, pass -Zprofile-hint-mostly-unused. However, since this option is a hint, using it without passing -Zprofile-hint-mostly-unused will only warn and ignore the profile option. Versions of Cargo prior to the introduction of this feature will give an "unused manifest key" warning, but will otherwise function without erroring. This allows using the hint in a crate's Cargo.toml without mandating the use of a newer Cargo to build it.

Unresolved Issues

No response

Future Extensions

In the future, we may also want to provide a way for a crate to hint that it should have this option turned on by default, unless overridden by the top-level crate.

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