Avoid parsing unchanged lockfiles - #17301
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weihanglo merged 1 commit intoAug 3, 2026
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Thanks. We actually had a similar PR (#17294) recently and got closed because it was a full bot automation not addressing reviewers' question correctly.
This seems to be a fairly pure refactor. Is there any reason it is still behind draft?
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I am also interested in how you fount this, if you don't mind sharing.
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Oops, sorry, took it out of draft!
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I tend to use Ultra mode to do exploration of projects and find interesting optimization opportunities, then will go deep on a few of them (try out a prototype, do some benchmarking, etc.). In this case I actually asked it to find opportunities "similar in spirit" to xmakro's Clippy optimizations which I found neat. It's a very different project though with very different bottlenecks so most of the surfaced findings were not that similar in spirit. I'm happy to share the full output if you want to see it (though it is of course LLM-generated).
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That sounds like a fun exploration!
We have a Performance label tracking those. One of the most possible area to improve is asyncifying Cargo. Cargo has its bespoke concurrency control before async/await. For example, dependency source update and manifest parsing are still serial. In #t-cargo > Parallelizing parts of cargo @Kobzol did an experiment on that but not yet ready.
Anyway, if you have found something interesting, feel free to open issues!
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Rust project may have an LLM policy soonish I guess, thoughif people bring a tidy-up doc and discuss with me as a human, personally I don't mind it is LLM-assisted or not.
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Update cargo submodule 21 commits in 7c83d4cc0953b81d823e47d640c64da9b8bd4fac..c79e8f89441b3e73d6d65d125c0c745792808c74 2026-07-29 21:34:53 +0000 to 2026-08-04 19:17:33 +0000 - fix(diag): Ensure diagnostic titles work without snippets (rust-lang/cargo#17304) - refactor: Remove unnecessary mut in sources (rust-lang/cargo#17305) - feat(trim-paths): emit unremap files for final artifacts (rust-lang/cargo#17303) - fix: prevent panic when `package.build` is empty (rust-lang/cargo#17268) - Add a suggestion when adding `[lints]` to a workspace to use `[workspace.lints]` instead (rust-lang/cargo#17300) - chore(deps): update embarkstudios/cargo-deny-action action to v2.1.1 (rust-lang/cargo#17291) - refactor: move sysroot lookup to GlobalContext (rust-lang/cargo#17276) - fix(trim-paths): unambiguous and reversible remap rules (rust-lang/cargo#17302) - Avoid parsing unchanged lockfiles (rust-lang/cargo#17301) - Remove unnecessary to_path_buf (rust-lang/cargo#17295) - chore(deps): update cargo-semver-checks to v0.50.0 (rust-lang/cargo#17297) - chore(deps): update actions/checkout action to v6.1.0 (rust-lang/cargo#17290) - Remove unnecessary return at end of functions (rust-lang/cargo#17292) - make __CARGO_TEST_FORCE_ARGFILE available in distributed builds (rust-lang/cargo#17293) - Fix manual_readme lint for lower-priority README files (rust-lang/cargo#17208) - fix(git): make checkout names independent of git config (rust-lang/cargo#17289) - fix(diag): Rename redundant_readme to manual_readme (rust-lang/cargo#17288) - Remove redundant double call .to_string() (rust-lang/cargo#17286) - fix(completions): complete paths for cargo run arguments (rust-lang/cargo#17284) - test(git): exercise multi git revision lockfile (rust-lang/cargo#17279) - add context to lints documentation (rust-lang/cargo#17273) r? ghost
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Update cargo submodule 21 commits in 7c83d4cc0953b81d823e47d640c64da9b8bd4fac..c79e8f89441b3e73d6d65d125c0c745792808c74 2026-07-29 21:34:53 +0000 to 2026-08-04 19:17:33 +0000 - fix(diag): Ensure diagnostic titles work without snippets (rust-lang/cargo#17304) - refactor: Remove unnecessary mut in sources (rust-lang/cargo#17305) - feat(trim-paths): emit unremap files for final artifacts (rust-lang/cargo#17303) - fix: prevent panic when `package.build` is empty (rust-lang/cargo#17268) - Add a suggestion when adding `[lints]` to a workspace to use `[workspace.lints]` instead (rust-lang/cargo#17300) - chore(deps): update embarkstudios/cargo-deny-action action to v2.1.1 (rust-lang/cargo#17291) - refactor: move sysroot lookup to GlobalContext (rust-lang/cargo#17276) - fix(trim-paths): unambiguous and reversible remap rules (rust-lang/cargo#17302) - Avoid parsing unchanged lockfiles (rust-lang/cargo#17301) - Remove unnecessary to_path_buf (rust-lang/cargo#17295) - chore(deps): update cargo-semver-checks to v0.50.0 (rust-lang/cargo#17297) - chore(deps): update actions/checkout action to v6.1.0 (rust-lang/cargo#17290) - Remove unnecessary return at end of functions (rust-lang/cargo#17292) - make __CARGO_TEST_FORCE_ARGFILE available in distributed builds (rust-lang/cargo#17293) - Fix manual_readme lint for lower-priority README files (rust-lang/cargo#17208) - fix(git): make checkout names independent of git config (rust-lang/cargo#17289) - fix(diag): Rename redundant_readme to manual_readme (rust-lang/cargo#17288) - Remove redundant double call .to_string() (rust-lang/cargo#17286) - fix(completions): complete paths for cargo run arguments (rust-lang/cargo#17284) - test(git): exercise multi git revision lockfile (rust-lang/cargo#17279) - add context to lints documentation (rust-lang/cargo#17273) r? ghost
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Update cargo submodule 21 commits in 7c83d4cc0953b81d823e47d640c64da9b8bd4fac..c79e8f89441b3e73d6d65d125c0c745792808c74 2026-07-29 21:34:53 +0000 to 2026-08-04 19:17:33 +0000 - fix(diag): Ensure diagnostic titles work without snippets (rust-lang/cargo#17304) - refactor: Remove unnecessary mut in sources (rust-lang/cargo#17305) - feat(trim-paths): emit unremap files for final artifacts (rust-lang/cargo#17303) - fix: prevent panic when `package.build` is empty (rust-lang/cargo#17268) - Add a suggestion when adding `[lints]` to a workspace to use `[workspace.lints]` instead (rust-lang/cargo#17300) - chore(deps): update embarkstudios/cargo-deny-action action to v2.1.1 (rust-lang/cargo#17291) - refactor: move sysroot lookup to GlobalContext (rust-lang/cargo#17276) - fix(trim-paths): unambiguous and reversible remap rules (rust-lang/cargo#17302) - Avoid parsing unchanged lockfiles (rust-lang/cargo#17301) - Remove unnecessary to_path_buf (rust-lang/cargo#17295) - chore(deps): update cargo-semver-checks to v0.50.0 (rust-lang/cargo#17297) - chore(deps): update actions/checkout action to v6.1.0 (rust-lang/cargo#17290) - Remove unnecessary return at end of functions (rust-lang/cargo#17292) - make __CARGO_TEST_FORCE_ARGFILE available in distributed builds (rust-lang/cargo#17293) - Fix manual_readme lint for lower-priority README files (rust-lang/cargo#17208) - fix(git): make checkout names independent of git config (rust-lang/cargo#17289) - fix(diag): Rename redundant_readme to manual_readme (rust-lang/cargo#17288) - Remove redundant double call .to_string() (rust-lang/cargo#17286) - fix(completions): complete paths for cargo run arguments (rust-lang/cargo#17284) - test(git): exercise multi git revision lockfile (rust-lang/cargo#17279) - add context to lints documentation (rust-lang/cargo#17273) r? ghost
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Update cargo submodule 21 commits in 7c83d4cc0953b81d823e47d640c64da9b8bd4fac..c79e8f89441b3e73d6d65d125c0c745792808c74 2026-07-29 21:34:53 +0000 to 2026-08-04 19:17:33 +0000 - fix(diag): Ensure diagnostic titles work without snippets (rust-lang/cargo#17304) - refactor: Remove unnecessary mut in sources (rust-lang/cargo#17305) - feat(trim-paths): emit unremap files for final artifacts (rust-lang/cargo#17303) - fix: prevent panic when `package.build` is empty (rust-lang/cargo#17268) - Add a suggestion when adding `[lints]` to a workspace to use `[workspace.lints]` instead (rust-lang/cargo#17300) - chore(deps): update embarkstudios/cargo-deny-action action to v2.1.1 (rust-lang/cargo#17291) - refactor: move sysroot lookup to GlobalContext (rust-lang/cargo#17276) - fix(trim-paths): unambiguous and reversible remap rules (rust-lang/cargo#17302) - Avoid parsing unchanged lockfiles (rust-lang/cargo#17301) - Remove unnecessary to_path_buf (rust-lang/cargo#17295) - chore(deps): update cargo-semver-checks to v0.50.0 (rust-lang/cargo#17297) - chore(deps): update actions/checkout action to v6.1.0 (rust-lang/cargo#17290) - Remove unnecessary return at end of functions (rust-lang/cargo#17292) - make __CARGO_TEST_FORCE_ARGFILE available in distributed builds (rust-lang/cargo#17293) - Fix manual_readme lint for lower-priority README files (rust-lang/cargo#17208) - fix(git): make checkout names independent of git config (rust-lang/cargo#17289) - fix(diag): Rename redundant_readme to manual_readme (rust-lang/cargo#17288) - Remove redundant double call .to_string() (rust-lang/cargo#17286) - fix(completions): complete paths for cargo run arguments (rust-lang/cargo#17284) - test(git): exercise multi git revision lockfile (rust-lang/cargo#17279) - add context to lints documentation (rust-lang/cargo#17273) r? ghost
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Update cargo submodule 21 commits in 7c83d4cc0953b81d823e47d640c64da9b8bd4fac..c79e8f89441b3e73d6d65d125c0c745792808c74 2026-07-29 21:34:53 +0000 to 2026-08-04 19:17:33 +0000 - fix(diag): Ensure diagnostic titles work without snippets (rust-lang/cargo#17304) - refactor: Remove unnecessary mut in sources (rust-lang/cargo#17305) - feat(trim-paths): emit unremap files for final artifacts (rust-lang/cargo#17303) - fix: prevent panic when `package.build` is empty (rust-lang/cargo#17268) - Add a suggestion when adding `[lints]` to a workspace to use `[workspace.lints]` instead (rust-lang/cargo#17300) - chore(deps): update embarkstudios/cargo-deny-action action to v2.1.1 (rust-lang/cargo#17291) - refactor: move sysroot lookup to GlobalContext (rust-lang/cargo#17276) - fix(trim-paths): unambiguous and reversible remap rules (rust-lang/cargo#17302) - Avoid parsing unchanged lockfiles (rust-lang/cargo#17301) - Remove unnecessary to_path_buf (rust-lang/cargo#17295) - chore(deps): update cargo-semver-checks to v0.50.0 (rust-lang/cargo#17297) - chore(deps): update actions/checkout action to v6.1.0 (rust-lang/cargo#17290) - Remove unnecessary return at end of functions (rust-lang/cargo#17292) - make __CARGO_TEST_FORCE_ARGFILE available in distributed builds (rust-lang/cargo#17293) - Fix manual_readme lint for lower-priority README files (rust-lang/cargo#17208) - fix(git): make checkout names independent of git config (rust-lang/cargo#17289) - fix(diag): Rename redundant_readme to manual_readme (rust-lang/cargo#17288) - Remove redundant double call .to_string() (rust-lang/cargo#17286) - fix(completions): complete paths for cargo run arguments (rust-lang/cargo#17284) - test(git): exercise multi git revision lockfile (rust-lang/cargo#17279) - add context to lints documentation (rust-lang/cargo#17273) r? ghost
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What does this PR try to resolve?
Previously, checking an unchanged lockfile with
--lockedor--frozendeserialized both lockfiles and rebuilt their resolution graphs before checking whether their contents already matched. For large workspaces, this repeats expensive work on the common unchanged-lockfile path.This PR moves the existing line-by-line equality check ahead of the semantic comparison. The existing line-ending behavior is preserved, and differing lockfiles still fall back to the full deserialization and resolution comparison.
On my M4, with 15 interleaved runs of
cargo metadata --offline --locked --format-version 1per workspace:How to test and review this PR?
The change only reorders the existing equality checks. All 24 lockfile compatibility integration tests pass, including coverage for frozen lockfile preservation and
--lockederrors.