feat(hints): support minimum optimization levels by 0xPoe · Pull Request #17368 · rust-lang/cargo

0xPoe · 2026-08-16T09:10:26Z

What does this PR try to resolve?

This PR would allow Rust library to provide a simple hint about the minimum opt-level to build them with via the hint.min-opt-level setting in the manifest.

How to test and review this PR?

Check the unit tests and review it commit by commit.

r?@ghost

0xPoe

🔢 Self-check (PR reviewed by myself and ready for feedback)

Code compiles successfully
Unit tests added
No AI-generated elegant nonsense in PR.
Comments added where necessary
PR title and description updated
Documentation updated
PR size is reasonable

r?@joshtriplett

View changes since this review

@ghost

### What does this PR try to resolve? Try to use `annotate-snippets` to report mostly unused warnings. Inspired by rust-lang#17368 (comment). Some behaviour changes after we move it to phase pass. | # | Case | Before | After | |---|---|---|---| | 1 | `hint-mostly-unused = true` in a profile table the build doesn't apply: unselected profile (`[profile.release]` on `cargo check`, config `profile.bench`), `build-override` with no build scripts, `package.<spec>` for a package that isn't built | Silent | Warns | | 2 | `hints.mostly-unused = true` while a profile sets `hint-mostly-unused = false` for that package | Silent, as the flag wouldn't change this build | Warns, as the key is still ignored without the flag (the profile override isn't considered) | | 3 | `hints.mostly-unused = true` while a profile also sets `hint-mostly-unused = true` for that package | Only the profile warning | Both warnings | | 4 | `[hints]` in a workspace member this invocation doesn't compile, e.g. `cargo check -p a` when `b` has the hint | Silent | Warns about `b` | | 5 | `cargo doc -p b` where `b` has `[hints]`| Silent | Warns | | 6 | `cargo clean` with `hint-mostly-unused = true` in a config/env profile | Silent | Warns, as `cargo clean` loads profiles | | 7 | `[hints]` in a path dependency that isn't a workspace member | Warns | Silent | | 8 | `[hints]` in a registry/git dependency | Warns under `-vv` when it is compiled | Silent | | 9 | `cargo install <registry crate>` whose own manifest has `[profile.release] hint-mostly-unused = true` | Warns | Silent | ### How to test and review this PR? Check the unit tests and review each commit individually. r?@ghost LLM disclosure: AI generated the unit tests and helped me move mostly unused diagnostics to the parse pass.

Record the current ignored-hint behavior across the RFC precedence, scope, validation, and boundary cases. Signed-off-by: 0xPoe <poe.liu@pm.me>

Validating `hints.min-opt-level` only needs the manifest, so run it as a package rule in the parse pass instead of walking the pre-build unit graph. Non-member path dependencies stop being diagnosed, matching how unused manifest keys and unknown hints are already reported. Signed-off-by: 0xPoe <poe.liu@pm.me>

Signed-off-by: 0xPoe <poe.liu@pm.me>

rustbot · 2026-10-04T19:26:57Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

0xPoe changed the title ~~feat(hints): support minimum optimization levels~~ WIP: feat(hints): support minimum optimization levels Aug 16, 2026

0xPoe changed the title ~~WIP: feat(hints): support minimum optimization levels~~ WIP(Not Ready For Review): feat(hints): support minimum optimization levels Aug 16, 2026

0xPoe force-pushed the hint-min-opt-level branch 7 times, most recently from b532a3f to 2b19c48 Compare August 21, 2026 07:18

0xPoe commented Aug 21, 2026

View reviewed changes

Comment thread crates/cargo-util-schemas/Cargo.toml Outdated

Comment thread crates/cargo-util-schemas/manifest.schema.json

Comment thread src/workspace/profiles.rs Outdated

rustbot assigned joshtriplett Aug 21, 2026

0xPoe changed the title ~~WIP(Not Ready For Review): feat(hints): support minimum optimization levels~~ feat(hints): support minimum optimization levels Aug 21, 2026

0xPoe marked this pull request as ready for review August 21, 2026 07:20

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 21, 2026