rustdoc: Only synthesize auto/blanket impls for documented items

[camelid]

Previously, the code would skip synthesizing impls if the trait was
not documented, but it would still synthesize even if the type was not
documented. This is wasted work.

[camelid]

This is based on #159721, so this should be rebased and get a perf run once that PR lands.

[rustbot]

r? @GuillaumeGomez

rustbot has assigned @GuillaumeGomez.
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: rustdoc
• rustdoc expanded to 8 candidates
• Random selection from GuillaumeGomez, lolbinarycat, notriddle

[camelid]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8d0c82f (8d0c82f4399e40d56ef07de43fedf554ddb93e9f)
Base parent: 2d8fa67 (2d8fa67781953811835f7ae45f670afbb7f44285)

[rust-timer]

Finished benchmarking commit (8d0c82f): 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)	-6.5%	[-19.1%, -0.8%]	11
Improvements ✅ (secondary)	-5.4%	[-13.7%, -0.3%]	3
All ❌✅ (primary)	-6.5%	[-19.1%, -0.8%]	11

Max RSS (memory usage)

Results (primary -1.6%, secondary -2.2%)

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)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-1.6%	[-2.0%, -1.3%]	4
Improvements ✅ (secondary)	-3.8%	[-4.9%, -1.6%]	3
All ❌✅ (primary)	-1.6%	[-2.0%, -1.3%]	4

Cycles

Results (primary -7.4%, secondary -6.5%)

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)	-7.4%	[-16.2%, -2.7%]	8
Improvements ✅ (secondary)	-9.8%	[-15.4%, -2.1%]	3
All ❌✅ (primary)	-7.4%	[-16.2%, -2.7%]	8

Binary size

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

Bootstrap: 488.662s -> 489.706s (0.21%)
Artifact size: 387.62 MiB -> 387.61 MiB (-0.00%)

[GuillaumeGomez]

Another great improvement, thanks a lot!

@bors r+ p=6 rollup=never

[rust-bors]

📌 Commit ab70c36 has been approved by GuillaumeGomez

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: GuillaumeGomez
Duration: 3h 10m 42s
Pushing 76c35a1 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 89c61a7 (parent) -> 76c35a1 (this PR)

Test differences

Show 2 test diffs

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

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 76c35a14a45897a366c11657ecbbe9ec4153ad17 --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. x86_64-gnu-gcc-core-tests: 14m 30s -> 8m 30s (-41.4%)
2. x86_64-gnu-tools: 43m 2s -> 55m 54s (+29.9%)
3. x86_64-gnu-llvm-21: 55m 27s -> 1h 11m (+29.6%)
4. optional-x86_64-gnu-parallel-frontend: 2h 9m -> 1h 31m (-29.2%)
5. dist-i686-msvc: 1h 29m -> 1h 55m (+28.7%)
6. x86_64-rust-for-linux: 36m 54s -> 47m 21s (+28.3%)
7. dist-powerpc64le-linux-musl: 1h 15m -> 1h 32m (+23.0%)
8. dist-arm-linux-gnueabi: 1h 9m -> 1h 24m (+21.6%)
9. arm-android: 1h 21m -> 1h 39m (+21.6%)
10. dist-armhf-linux: 1h 26m -> 1h 7m (-21.5%)

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 (76c35a1): 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)	-6.5%	[-19.1%, -0.8%]	11
Improvements ✅ (secondary)	-5.4%	[-13.8%, -0.3%]	3
All ❌✅ (primary)	-6.5%	[-19.1%, -0.8%]	11

Max RSS (memory usage)

Results (primary -1.8%, secondary -1.2%)

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)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-1.8%	[-2.0%, -1.5%]	4
Improvements ✅ (secondary)	-3.1%	[-4.8%, -1.4%]	2
All ❌✅ (primary)	-1.8%	[-2.0%, -1.5%]	4

Cycles

Results (primary -7.4%, secondary -3.8%)

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-7.4%	[-16.3%, -2.1%]	9
Improvements ✅ (secondary)	-5.9%	[-11.9%, -2.6%]	3
All ❌✅ (primary)	-7.4%	[-16.3%, -2.1%]	9

Binary size

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

Bootstrap: 487.226s -> 488.274s (0.22%)
Artifact size: 387.62 MiB -> 387.66 MiB (0.01%)