Stabilize expr_2021 fragment specifier in all editions

[eholk]

This is part of the expr/expr_2021 fragment specifier for Edition 2024 (#123742). The RFC says we can support expr_2021 in as many editions as is practical, and there's nothing particularly hard about supporting it all the way back to 2015.

In editions 2021 and earlier, expr and expr_2021 are synonyms. Their behavior diverges starting in Edition 2024. This is checked by the expr_2021_inline_const.rs test.

cc @vincenzopalazzo @rust-lang/wg-macros @traviscross

[rustbot]

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[traviscross]

@rustbot labels +I-lang-nominated

Thanks for the stabilization PR. Let's nominate to have a look.

[compiler-errors]

r=me after T-lang deals with this

[traviscross]

On the lang side, we last discussed this specifier on 2024-08-28 (in deciding to keep the name) and also noted in that discussion wanting to get this stabilized as soon as possible. This is that stabilization, so let's...

@rfcbot fcp merge

[traviscross]

@rfcbot fcp merge

[rfcbot]

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

• @joshtriplett
• @nikomatsakis
• @pnkfelix
• @scottmcm
• @tmandry
• @traviscross

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[tmandry]

@rfcbot reviewed

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[eholk]

@bors r=@compiler-errors

[bors]

📌 Commit 52e36f8 has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 52e36f8 with merge ece67f5...

[bors]

💔 Test failed - checks-actions

[vincenzopalazzo]

Small rebased and added the following diff!

diff --git a/tests/ui/macros/metavar_cross_edition_recursive_macros.rs b/tests/ui/macros/metavar_cross_edition_recursive_macros.rs
index 3eec1208b89..9a5b92f5032 100644
--- a/tests/ui/macros/metavar_cross_edition_recursive_macros.rs
+++ b/tests/ui/macros/metavar_cross_edition_recursive_macros.rs
@@ -6,7 +6,6 @@
 // This test captures the behavior of macro-generating-macros with fragment
 // specifiers across edition boundaries.

-#![feature(expr_fragment_specifier_2024)]
 #![feature(macro_metavar_expr)]
 #![allow(incomplete_features)]

Giving a CI run before squash the fixup commit!

[traviscross]

@bors r=compiler-errors,traviscross

[bors]

📌 Commit c7cd55f has been approved by compiler-errors,traviscross

It is now in the queue for this repository.

[bors]

⌛ Testing commit c7cd55f with merge 21aa500...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors,traviscross
Pushing 21aa500 to master...

[rust-timer]

Finished benchmarking commit (21aa500): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (secondary 6.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	6.5%	[6.1%, 7.4%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 769.179s -> 771.18s (0.26%)
Artifact size: 341.45 MiB -> 341.46 MiB (0.00%)