Optimizing Clippy & linting

[nikomatsakis]

Metadata
Owner(s)	@blyxyas
Team(s)	clippy
Goal document	2024h2/optimize-clippy

Summary

This is the formalization and documentation of the Clippy Performance Project, a project first talked about on Zulip, July 2023. As the project consists of several points and is ever-changing, this document also has a dynamic structure and the team can add points.

In short, this is an effort to optimize Clippy, and Rust's linting infrastructure with a point of view of making Clippy faster (both on CI/CD pipelines, and on devs' machines)

Tasks and status

• (Big performance change) Do not run lints that cannot emit rust#125116 Merged
• Incremental lints implemented

[blyxyas]

✔️ New medium-sized objective completed

rust-lang/rust-clippy#12830 Use ControlFlow in more places, closing rust-lang/rust-clippy#12829 Use ControlFlow in more visitors

[nikomatsakis]

This issue is intended for status updates only.

For general questions or comments, please contact the owner(s) directly.

[blyxyas]

Key developments:

• 1 Issue open with performance-project label ([Project Goal, Help Wanted] Optimizing MSRV attribute collection rust-clippy#13169), we've already integrated it into the project. @Alexendoo will be taking a look at it for the time being.
• 1 performance PR merged (see above comment)
• We're remaking our benchmarking tool (becnhv2)

  Our last benchmarking tool (becnh) wasn't actually benchmarking the way we would've liked. I'm currently remaking it from scratch, this time in Rust instead of Bash. See here and here for more details

What's to come:

• After becnhv2 is done, we'll continue working on (Big performance change) Do not run lints that cannot emit rust#125116 (which currently needs rebasing).

Blockers: There are no blockers, although we need some help figuring out the main bug on rust-lang/rust#125116, explained here. Someone from the compiler team taking a look at it would be greatly appreciated

[blyxyas]

Key developments:

• (Big performance change) Do not run lints that cannot emit rust#125116 is now all green! 🎉 We're currently doing benchmarks.
• (Clippy compilation) I'm working on moving our declare_clippy_lint macro from procedural to a macro_rules one.
• 1 Issue open (proposal) with the performance project label ([CI] Use rust-cache@v2 when building on CI rust-clippy#13033)

Blockers:
There are no blockers.

[blyxyas]

Key developments:
- GnomedDev pushed rust-lang/rust#130553, which replaced an old Clippy infrastructure with a faster one (string matching into symbol matching)
- Inspections into Clippy's type sizes and cache alignment are being started. Nothing fruitful yet, but I'm checking if there's something to be improved.
- The WIP benchmarking tool for Clippy has changed the algorithm from git based to using static source code distributions (like rustup), I'm experimenting with more possibilities.

Blockers:
There are no blockers

[blyxyas]

✔️ New large objective completed

rust-lang/rust#125116 has been merged, marking half of our goal formally done!