Recover and suggest to use `;` to construct array type #143905

xizheyin · 2025-07-13T20:32:08Z

r? compiler

xizheyin · 2025-07-13T20:37:28Z

tests/ui/parser/recover/array-type-no-semi.stderr

+help: use `=` if you meant to assign
+   |
+LL -     let b: [i32, 5];
+LL +     let b = [i32, 5];


This suggestion is wrong, but it have nothing with this PR. Because the old diagnostic has the same help message.

Old Diagnostic:

error: expected one of `!`, `(`, `+`, `::`, `;`, `<`, or `]`, found `,` --> src/main.rs:3:16 | 3 | let b: [i32, 5]; | - ^ expected one of 7 possible tokens | | | while parsing the type for `b` | help: use `=` if you meant to assign

compiler/rustc_parse/src/parser/ty.rs

compiler-errors · 2025-07-13T21:27:28Z

r? compiler-errors

@rustbot author

rustbot · 2025-07-13T21:27:33Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

xizheyin · 2025-07-14T01:07:50Z

Also, why can't we emit the error and then return TyKind::Array, so we can recover successfully rather than propagating an error?

Yeah, I have tried to recover it to TyKind::Array, but It emit a regression. In this test, it will emit error: expected ; or ], found , immidiately, which is wrong. It just want call parse_ty_common for Some(x), while in this case, it parse it into Array and give a wrong suggestion.

https://github.com/rust-lang/rust/blob/master/tests/ui/issues/issue-50571.rs
https://github.com/rust-lang/rust/blob/master/tests/ui/issues/issue-50571.stderr

@rustbot ready

compiler-errors

I personally think it's fine to regress #50571, since it's an issue that only has to do with edition 2015 and is a rare enough.

I'd still like to see a better recovery that actually ends up returning Ok(TyKind::Array(...)).

tests/ui/parser/better-expected.stderr

compiler/rustc_parse/src/parser/ty.rs

Signed-off-by: xizheyin <[email protected]>

xizheyin

@rustbot ready

xizheyin · 2025-07-14T06:46:58Z

tests/ui/parser/removed-syntax/removed-syntax-fixed-vec.stderr

+help: you might have meant to use `;` as the separator
+   |
+LL | type v = [isize ;* 3];
+   |                 +


This regression is somewhat werid, because parse_expr_anon_const take it as a deref of 3. That maybe reasonable for

const L = &3; type V = [isize * L];

After applying the suggestion, it is correct.

type V = [isize ;* L];

But IMO, it does not matter in this * case, because after applying the suggestion, compiler will report something like you can not deref a integer, which is reasonable.

We could perhaps special case both , and * as separators here?

xizheyin · 2025-07-14T06:47:57Z

tests/ui/parser/recover/array-type-no-semi.stderr

+error: expected `;` or `]`, found `5`
+  --> $DIR/array-type-no-semi.rs:15:17
+   |
+LL |     let e: [i32 5];
+   |                 ^ expected `;` or `]`
+   |
+   = note: you might have meant to write a slice or array type
+help: you might have meant to use `;` as the separator
+   |
+LL |     let e: [i32 ;5];
+   |                 +


Here is the new case like [i32 5].

rustbot · 2025-07-14T08:02:55Z

There are changes to the tidy tool.

cc @jieyouxu

tests/ui/issues/issue-50571.rs

compiler-errors · 2025-07-14T17:12:53Z

tests/ui/parser/removed-syntax/removed-syntax-fixed-vec.stderr

+help: you might have meant to use `;` as the separator
+   |
+LL | type v = [isize ;* 3];
+   |                 +


We could perhaps special case both , and * as separators here?

compiler-errors · 2025-07-14T17:14:24Z

compiler/rustc_parse/src/parser/ty.rs

+        let length = match self.parse_expr_anon_const() {
+            Ok(length) => length,
+            Err(e) => {
+                e.cancel();
+                self.bump();
+                match self.parse_expr_anon_const() {


Instead of parsing once then parsing again, could you do:

let suggestion_span = if self.eat(comma) || self.eat(asterisk) { // Consume common erroneous separators. self.prev_token.span } else { self.token.span.shrink_to_lo() }; /// then parse the length.

Should other separators be considered, such as :?

I think , and * are fine for now

Signed-off-by: xizheyin <[email protected]>

xizheyin · 2025-07-15T04:02:32Z

Yeah, I have instead specially judge , and *.

compiler-errors · 2025-07-15T05:47:28Z

@bors r+ rollup

bors · 2025-07-15T05:47:31Z

📌 Commit ed88af2 has been approved by compiler-errors

It is now in the queue for this repository.

Rollup of 13 pull requests Successful merges: - #142301 (tests: Fix duplicated-path-in-error fail with musl) - #143630 (Drop `./x suggest`) - #143736 (Give all bytes of TypeId provenance) - #143752 (Don't panic if WASI_SDK_PATH not set when detecting compiler) - #143837 (Adjust `run_make_support::symbols` helpers) - #143878 (Port `#[pointee]` to the new attribute parsing infrastructure) - #143905 (Recover and suggest to use `;` to construct array type) - #143907 (core: make `str::split_at_unchecked()` inline) - #143910 (Add experimental `backtrace-trace-only` std feature) - #143927 (Preserve constness in trait objects up to hir ty lowering) - #143935 (rustc_type_ir/walk: move docstring to `TypeWalker` itself) - #143938 (Update books) - #143941 (update `cfg_select!` documentation) Failed merges: - #143926 (Remove deprecated fields in bootstrap) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143905 - xizheyin:143828, r=compiler-errors Recover and suggest to use `;` to construct array type Fixes #143828 r? compiler

Rollup of 13 pull requests Successful merges: - rust-lang/rust#142301 (tests: Fix duplicated-path-in-error fail with musl) - rust-lang/rust#143630 (Drop `./x suggest`) - rust-lang/rust#143736 (Give all bytes of TypeId provenance) - rust-lang/rust#143752 (Don't panic if WASI_SDK_PATH not set when detecting compiler) - rust-lang/rust#143837 (Adjust `run_make_support::symbols` helpers) - rust-lang/rust#143878 (Port `#[pointee]` to the new attribute parsing infrastructure) - rust-lang/rust#143905 (Recover and suggest to use `;` to construct array type) - rust-lang/rust#143907 (core: make `str::split_at_unchecked()` inline) - rust-lang/rust#143910 (Add experimental `backtrace-trace-only` std feature) - rust-lang/rust#143927 (Preserve constness in trait objects up to hir ty lowering) - rust-lang/rust#143935 (rustc_type_ir/walk: move docstring to `TypeWalker` itself) - rust-lang/rust#143938 (Update books) - rust-lang/rust#143941 (update `cfg_select!` documentation) Failed merges: - rust-lang/rust#143926 (Remove deprecated fields in bootstrap) r? `@ghost` `@rustbot` modify labels: rollup

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Add test array-type-no-semi.rs

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Signed-off-by: xizheyin <[email protected]>

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xizheyin force-pushed the 143828 branch from edd7377 to cc95190 Compare July 14, 2025 08:02

rustbot added A-tidy Area: The tidy tool T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Jul 14, 2025

xizheyin changed the title ~~Suggest use ; to construct array type when other token exists~~ Recover and suggest to use ; to construct array type Jul 14, 2025

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Recover and suggest use ; to construct array type

ed88af2

Signed-off-by: xizheyin <[email protected]>

xizheyin force-pushed the 143828 branch from a4f7e21 to ed88af2 Compare July 15, 2025 04:01

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Rollup of 13 pull requests #143958

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bors merged commit 281990e into rust-lang:master Jul 15, 2025
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Unrolled build for #143905

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Rollup merge of #143905 - xizheyin:143828, r=compiler-errors Recover and suggest to use `;` to construct array type Fixes #143828 r? compiler

xizheyin deleted the 143828 branch July 15, 2025 18:00

Recover and suggest to use ; to construct array type #143905

Recover and suggest to use ; to construct array type #143905

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Recover and suggest to use `;` to construct array type #143905

Recover and suggest to use `;` to construct array type #143905

xizheyin commented Jul 13, 2025 •

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