Tracking Issue: Exposing RUSTFLAGS in cargo

[epage]

RUSTFLAGS is a low level mechanism

• Harder for users to discover features
• Harder for cargo to reason about like in Per-user compiled artifact cache #5931, add a RUSTLINKFLAGS environment variable #4349

This is meant to track the RUSTFLAGS that should have a cargo-native way of being exposed. This won't always be one-to-one mappings and won't necessarily cover every rustc CLI feature.

• --allow, --deny, --warn
  • Use case: package-level control over warnings
  • Tracking Issue for [lints] table RFC 3389 #12115
• --allow, --deny, --warn
  • Interactively denying/allowing warnings
  • Add --deny-warnings functionality for all commands. #8424
• --target-cpu=native
  • Expose target-cpu=native as a profile setting #2535
• --cfg
  • https://internals.rust-lang.org/t/pre-rfc-mutually-excusive-global-features/19618
• -Cinstrument-coverage
  • Native cargo coverage support #13040
• -C target-feature
  • Consider exposing target_feature option in cargo CLI #14524

Note: Keep in mind the cargo-native solution could live in:

• Cargo.toml: if this is something considered static for the project
• .cargo/config.toml (which includes env, cli): if this is something that changes between environments (including users and platforms) or is transient
• CLI: if this is something that changes from run to run and needs the extra visibility

See also

• https://rust-lang.zulipchat.com/#narrow/stream/246057-t-cargo/topic/Reasons.20people.20use.20RUSTFLAGS
• https://rust-lang.zulipchat.com/#narrow/stream/246057-t-cargo/topic/Per-user.20build.20caches

[soloturn]

@epage is this the same as people always discuss when finding the config language toml is ok, but not ideal? compared to:

• ron: https://github.com/ron-rs/ron
• cuddle: https://kdl.dev
• dhall: https://dhall-lang.org/

[epage]

This issue is about finding ways to expose environment config as project config and is unrelated to what format is used for either