Lang item cleanups

[oli-obk]

a grab bag of cleanups around lang item collection and various documentation things I found while poking around that area

r? @JonathanBrouwer

[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

[rustbot]

JonathanBrouwer is currently at their maximum review capacity.
They may take a while to respond.

[oli-obk]

@bors try @rust-timer queue

[bjorn3]

Another minor cleanup: WEAK_ONLY_LANG_ITEMS doesn't look to be used anywhere. Only LangItem::is_weak_only is used.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 80e7599 (80e75997d7b5e008b36315517f09f1b92496d928)
Base parent: 07074cf (07074cfe1d991fe06b7fc613bbbd1dd9d0d37c80)

[rust-timer]

Finished benchmarking commit (80e7599): 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
@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)	-0.3%	[-0.5%, -0.2%]	39
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.1%]	42
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	39

Max RSS (memory usage)

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

Cycles

Results (secondary 0.8%)

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)	2.4%	[1.9%, 2.8%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 489.352s -> 489.442s (0.02%)
Artifact size: 388.43 MiB -> 388.34 MiB (-0.02%)