Try to recover from over-parsing in const item with missing semicolon by chenyukang · Pull Request #151247 · rust-lang/rust

chenyukang · 2026-01-17T13:31:34Z

Fixes #151149

r? @estebank

compiler/rustc_parse/src/parser/item.rs

tests/ui/issues/const-recover-semi-issue-151149.rs

compiler/rustc_parse/src/parser/item.rs

tests/ui/issues/const-recover-semi-issue-151149.stderr

estebank · 2026-01-19T00:31:12Z

tests/ui/issues/const-recover-semi-issue-151149.stderr

+error[E0308]: mismatched types
+  --> $DIR/const-recover-semi-issue-151149.rs:15:19
+   |
+LL | const fn foo() -> &'static u8 {
+   |          ---      ^^^^^^^^^^^ expected `&u8`, found `()`
+   |          |
+   |          implicitly returns `()` as its body has no tail or `return` expression


It'd be lovely if we could mark the function's tail expr as TyKind::Err so that we didn't emit a second error...

is there any flag from parser we can set it directly?

commit 471b929 will remove the later mismatched error, not sure there is any simpler solution, seems a little over engineering for a corner case.

estebank · 2026-01-19T17:51:01Z

tests/ui/parser/const-recover-semi-issue-151149.stderr

+  --> $DIR/const-recover-semi-issue-151149.rs:19:38
+   |
+LL |       const C: u8 = u8::const_default()
+   |  ______________________________________^


The span should start where the const starts (as the label is talking about it but pointing at the rhs of the binop).

tests/ui/parser/const-recover-semi-issue-151149.stderr

estebank · 2026-01-20T03:25:51Z

tests/ui/parser/const-recover-semi-issue-151149.rs

@@ -0,0 +1,38 @@
+#![feature(const_trait_impl)]


Can we make this //@ run-rustfix?

compiler/rustc_parse/src/parser/mod.rs

…ssing

rustbot · 2026-02-01T03:46:20Z

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 · 2026-02-01T03:49:31Z

i'd like to see whether there is a performance regression.

@bors try @rust-timer queue

…=<try> Try to recover from over-parsing in const item with missing semicolon

chenyukang · 2026-02-01T05:02:33Z

@bors retry

rust-bors · 2026-02-01T05:02:35Z

❗ You can only retry pull requests that are approved and have a previously failed auto build.

rust-bors · 2026-02-01T05:59:49Z

☀️ Try build successful (CI)
Build commit: f37f3df (f37f3dfb6a344f1fe12b003fdaeaf36417406168, parent: a1db344c0829cb682df4174e9370b60915751605)

rust-timer · 2026-02-01T06:40:52Z

Finished benchmarking commit (f37f3df): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in 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)	0.1%	[0.1%, 0.1%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -5.1%, secondary -3.1%)

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)	-5.1%	[-5.1%, -5.1%]	1
Improvements ✅ (secondary)	-3.1%	[-3.1%, -3.1%]	1
All ❌✅ (primary)	-5.1%	[-5.1%, -5.1%]	1

Cycles

Results (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)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.8%	[-4.8%, -4.8%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.1%, secondary -0.1%)

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)	-0.1%	[-0.1%, -0.0%]	44
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	24
All ❌✅ (primary)	-0.1%	[-0.1%, -0.0%]	44

Bootstrap: 476.042s -> 475.011s (-0.22%)
Artifact size: 397.86 MiB -> 397.80 MiB (-0.02%)

- Change error span to start from 'const' keyword instead of binop RHS - Add decl_lo parameter to missing_semi_from_binop() for better spans - Add run-rustfix directive to test file - Simplify test to focus on const item recovery cases

rustbot assigned estebank Jan 17, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 17, 2026

chenyukang commented Jan 17, 2026

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compiler/rustc_parse/src/parser/item.rs Outdated Show resolved Hide resolved

chenyukang force-pushed the yukang-fix-const-recover-151149 branch from 0851ad6 to b1dcdd1 Compare January 17, 2026 16:52

estebank reviewed Jan 19, 2026

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chenyukang force-pushed the yukang-fix-const-recover-151149 branch 2 times, most recently from acb4b6a to 68d28b5 Compare January 19, 2026 07:25

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estebank reviewed Jan 20, 2026

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chenyukang added 3 commits February 1, 2026 03:31

Try to recover from over-parsing in const item when a semicolon is mi…

8048fbb

…ssing

also add recover from over parsing for let

e92eb4d

remove mismatched errors when recovered

fb11399

chenyukang force-pushed the yukang-fix-const-recover-151149 branch from 2c3d8d3 to c639215 Compare February 1, 2026 03:46

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rust-bors bot pushed a commit that referenced this pull request Feb 1, 2026

Auto merge of #151247 - chenyukang:yukang-fix-const-recover-151149, r…

f37f3df

…=<try> Try to recover from over-parsing in const item with missing semicolon

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 1, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 1, 2026

chenyukang force-pushed the yukang-fix-const-recover-151149 branch from c639215 to a393b01 Compare February 1, 2026 06:52

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rust-timer commented Feb 1, 2026

Overall result: ❌ regressions - no action needed

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chenyukang commented Jan 17, 2026 •

edited by rustbot

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