Refactor the #[allow(dead_code)] propagation for impl items of traits

[mu001999]

View all comments

Extracted from #157885.

This PR does the refactor and corrects the previous implementation.

The following will fail currently (play):

#![deny(dead_code)]
#![deny(unfulfilled_lint_expectations)]

#[allow(dead_code)]
pub trait Tr {
    fn foo(&self);
}

struct Foo;

impl Tr for Foo {
    fn foo(&self) {
        bar();
    }
}

#[expect(dead_code)]
fn bar() {}

fn main() {}

After this PR, we could handle the #[allow(dead_code)] propagation correctly, and should get perf improvement.

[mu001999]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: ef781c8 (ef781c8005ba42aaa03739a3effec6ddb8e82cbe)
Base parent: 2f54787 (2f54787b636028a19294176d0fb27794452e6608)

[rust-timer]

Finished benchmarking commit (ef781c8): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-1.3%, -0.2%]	35
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.1%]	9
All ❌✅ (primary)	-0.5%	[-1.3%, -0.2%]	35

Max RSS (memory usage)

Results (secondary 5.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	5.9%	[5.9%, 5.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 3.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.7%	[2.7%, 7.2%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.5%	[-3.5%, -3.5%]	1
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 470.877s -> 469.545s (-0.28%)
Artifact size: 400.19 MiB -> 400.97 MiB (0.19%)

[rustbot]

r? @chenyukang

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: compiler
• compiler expanded to 75 candidates
• Random selection from 18 candidates

[mu001999]

@rustbot author

[mu001999]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: e466d2a (e466d2ab296542be4a4e93a797980f81378d18a4)
Base parent: da51146 (da5114692c9ebe46b869488c5f34f92eb10b98c1)

[rust-timer]

Finished benchmarking commit (e466d2a): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	2
Improvements ✅ (primary)	-0.5%	[-1.3%, -0.1%]	37
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.1%]	10
All ❌✅ (primary)	-0.5%	[-1.3%, -0.1%]	37

Max RSS (memory usage)

Results (secondary 7.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	7.7%	[7.7%, 7.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -3.1%, secondary -3.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.2%, -3.1%]	2
Improvements ✅ (secondary)	-3.7%	[-3.7%, -3.7%]	1
All ❌✅ (primary)	-3.1%	[-3.2%, -3.1%]	2

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 469.244s -> 471.227s (0.42%)
Artifact size: 400.19 MiB -> 400.33 MiB (0.03%)

[rustbot]

This PR was rebased onto a different main 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.

[chenyukang]

@bors r+ rollup

[rust-bors]

📌 Commit 93d03be has been approved by chenyukang

It is now in the queue for this repository.

[mu001999]

This PR has perf implication, so @bors rollup=never

[rust-log-analyzer]

The job x86_64-mingw-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[rust-bors]

💔 Test for 62090b5 failed: CI. Failed job:

• auto - x86_64-mingw-1 (web logs, enhanced plaintext logs)

[mu001999]

failures:

---- library\std\src\os\windows\process.rs - os::windows::process::CommandExt::spawn_with_attributes (line 317) stdout ----
Test executable failed (exit code: 101).

stdout:
Microsoft Windows [Version 10.0.26100.33296]
(c) Microsoft Corporation. All rights reserved.

D:\a\rust\rust\library\std>
stderr:

thread 'main' (3256) panicked at library\std\src\os\windows\process.rs:31:63:
called `Result::unwrap()` on an `Err` value: Os { code: 5, kind: PermissionDenied, message: "Access is denied." }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- library\std\src\os\windows\process.rs - os::windows::process::CommandExt::spawn_with_attributes (line 317) stdout end ----

failures:
    library\std\src\os\windows\process.rs - os::windows::process::CommandExt::spawn_with_attributes (line 317)

test result: FAILED. 1261 passed; 1 failed; 177 ignored; 0 measured; 0 filtered out; finished in 144.40s

all doctests ran in 147.84s; merged doctests compilation took 3.05s
error: doctest failed, to rerun pass `-p std --doc`
Bootstrap failed while executing `test --stage 2 --skip=compiler --skip=src`
Currently active steps:
test::Crate { build_compiler: Compiler { stage: 2, host: x86_64-pc-windows-gnu, forced_compiler: false }, target: x86_64-pc-windows-gnu, mode: Std, crates: ["alloc", "alloctests", "compiler_builtins", "core", "coretests", "panic_abort", "panic_unwind", "proc_macro", "rustc-std-workspace-core", "std", "std_detect", "sysroot", "test", "unwind"] } at src\bootstrap\src\core\build_steps\test.rs:3523
Build completed unsuccessfully in 2:20:01
make: *** [Makefile:126: ci-mingw-x] Error 1
  local time: Fri Aug 28 07:56:07 CUT 2026
  network time: Fri, 28 Aug 2026 07:56:08 GMT
##[error]Process completed with exit code 2.

Seems suspicious

@bors retry

[rust-bors]

☀️ Test successful - CI
Approved by: chenyukang
Duration: 3h 19m 45s
Pushing c42ac5f to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing d0f2ef5 (parent) -> c42ac5f (this PR)

Test differences

Show 5 test diffs

Stage 1

• [ui (polonius)] tests/ui/lint/dead-code/allow-dead-code-propagation-to-impls.rs: [missing] -> pass (J0)
• [ui] tests/ui/lint/dead-code/allow-dead-code-propagation-to-impls.rs: [missing] -> pass (J1)

Stage 2

• [ui] tests/ui/lint/dead-code/allow-dead-code-propagation-to-impls.rs: [missing] -> pass (J2)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: x86_64-gnu-next-trait-solver-polonius
• J1: x86_64-gnu-llvm-21-3, x86_64-gnu-llvm-22-3, x86_64-gnu-next-trait-solver-polonius
• J2: aarch64-apple-1, aarch64-apple-macos-26-1, aarch64-gnu, aarch64-gnu-llvm-21-1, aarch64-msvc-1, arm-android, armhf-gnu, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-gcc, x86_64-gnu-llvm-21, x86_64-gnu-llvm-21-2, x86_64-gnu-llvm-22-2, x86_64-gnu-nopt, x86_64-gnu-parallel-frontend, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard c42ac5fd59628ea7e2f52af5944c2aaac3f0e7f6 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. i686-gnu-nopt-2: 1h 27m -> 2h 12m (+50.1%)
2. i686-msvc-2: 1h 28m -> 2h 8m (+45.2%)
3. x86_64-gnu-gcc-core-tests: 17m 41s -> 10m (-43.4%)
4. dist-x86_64-netbsd: 1h 4m -> 1h 31m (+41.8%)
5. x86_64-gnu-stdlib-semver-check: 18m 5s -> 11m 20s (-37.3%)
6. x86_64-rust-for-linux: 59m 7s -> 37m 19s (-36.9%)
7. dist-x86_64-llvm-mingw: 2h 7m -> 1h 25m (-32.9%)
8. x86_64-gnu-llvm-21-3: 1h 11m -> 1h 34m (+32.8%)
9. x86_64-mingw-1: 2h 16m -> 3h (+31.8%)
10. i686-gnu-nopt-1: 2h 23m -> 1h 38m (-31.3%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (c42ac5f): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-1.3%, -0.1%]	32
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	8
All ❌✅ (primary)	-0.5%	[-1.3%, -0.1%]	32

Max RSS (memory usage)

Results (primary -2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Cycles

Results (primary -2.4%, secondary 3.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.3%	[3.3%, 3.3%]	1
Improvements ✅ (primary)	-2.4%	[-2.7%, -2.2%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.4%	[-2.7%, -2.2%]	3

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 475.629s -> 474.678s (-0.20%)
Artifact size: 402.76 MiB -> 402.79 MiB (0.01%)