Remove skip_arg attribute from Diagnostic and Subdiagnostic proc-macros

[GuillaumeGomez]

Instead of having users to manually add #[skip_arg] for each field that is not used in fluent messages, I think it's better to instead let the proc-macro only call diag.arg("name", field) on the fields actually used.

r? @JonathanBrouwer

[rustbot]

The rustc-dev-guide subtree was changed. If this PR only touches the dev guide consider submitting a PR directly to rust-lang/rustc-dev-guide otherwise thank you for updating the dev guide with your changes.

cc @BoxyUwU, @tshepang

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

rustc_macros::diagnostics was changed

cc @TaKO8Ki, @JonathanBrouwer

The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

Some changes occurred in match checking

cc @Nadrieril

[GuillaumeGomez]

I didn't expect to ping half the compiler team though. O.o

[JonathanBrouwer]

@bors try @rust-timer queue
Just in case

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8f93c9d (8f93c9d17d1ef0821b932d7ec77d1f88c1687baa, parent: b5e038d7158c1af55a646027fdacf5ecd7c783c7)

[rust-timer]

Finished benchmarking commit (8f93c9d): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary 15.5%, secondary -1.7%)

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

	mean	range	count
Regressions ❌ (primary)	15.5%	[15.5%, 15.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.7%	[-2.5%, -0.8%]	2
All ❌✅ (primary)	15.5%	[15.5%, 15.5%]	1

Cycles

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

Binary size

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

Bootstrap: 512.125s -> 509.812s (-0.45%)
Artifact size: 400.67 MiB -> 400.68 MiB (0.00%)