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Handle unbalanced delimiters gracefully in make_attr_token_stream #151948

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Merged
rust-bors merged 1 commit into from
Feb 2, 2026
Merged

Handle unbalanced delimiters gracefully in make_attr_token_stream #151948

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8 changes: 7 additions & 1 deletion compiler/rustc_ast/src/tokenstream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -354,7 +354,13 @@ fn make_attr_token_stream(
FrameData { open_delim_sp: Some((delim, span, spacing)), inner: vec![] },
));
} else if let Some(delim) = kind.close_delim() {
let frame_data = mem::replace(&mut stack_top, stack_rest.pop().unwrap());
// If there's no matching opening delimiter, the token stream is malformed,
// likely due to a improper delimiter positions in the source code.
// It's not delimiter mismatch, and lexer can not detect it, so we just ignore it here.
let Some(frame) = stack_rest.pop() else {
return AttrTokenStream::new(stack_top.inner);
};
let frame_data = mem::replace(&mut stack_top, frame);
let (open_delim, open_sp, open_spacing) = frame_data.open_delim_sp.unwrap();
assert!(
open_delim.eq_ignoring_invisible_origin(&delim),
Expand Down
22 changes: 22 additions & 0 deletions tests/ui/macros/tokenstream-ice-issue-149954.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
// Regression test for ICE https://github.com/rust-lang/rust/issues/149954
//@ edition: 2024

enum A {
A
const A: A = { //~ ERROR expected one of `(`, `,`, `=`, `{`, or `}`, found keyword `const`
#[derive(Debug)]
struct A
where
A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
//~^ ERROR malformed `cfg` attribute input
//~| ERROR malformed `cfg` attribute input
//~| ERROR expected trait, found struct `A`
//~| ERROR expected trait, found type parameter `A`
//~| ERROR expected trait, found struct `A`
//~| ERROR expected trait, found type parameter `A`
//~| ERROR expected one of `<`, `where`, or `{`, found `}`
//~| ERROR expected one of `<`, `where`, or `{`, found `}`
//~| ERROR expected one of `,`, `>`, or `}`, found `<eof>`
}
>;
}; //~ ERROR `main` function not found in crate
110 changes: 110 additions & 0 deletions tests/ui/macros/tokenstream-ice-issue-149954.stderr
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@@ -0,0 +1,110 @@
error: expected one of `(`, `,`, `=`, `{`, or `}`, found keyword `const`
--> $DIR/tokenstream-ice-issue-149954.rs:6:5
|
LL | A
| - expected one of `(`, `,`, `=`, `{`, or `}`
LL | const A: A = {
| ^^^^^ unexpected token
|
= help: enum variants can be `Variant`, `Variant = <integer>`, `Variant(Type, ..., TypeN)` or `Variant { fields: Types }`

error: expected one of `<`, `where`, or `{`, found `}`
--> $DIR/tokenstream-ice-issue-149954.rs:10:60
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| - ^ expected one of `<`, `where`, or `{`
| |
| while parsing this enum

error: expected one of `<`, `where`, or `{`, found `}`
--> $DIR/tokenstream-ice-issue-149954.rs:10:60
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| - ^ expected one of `<`, `where`, or `{`
| |
| while parsing this enum
|
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: expected one of `,`, `>`, or `}`, found `<eof>`
--> $DIR/tokenstream-ice-issue-149954.rs:10:60
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| ^ expected one of `,`, `>`, or `}`
|
help: you might have meant to end the type parameters here
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }>
| +

error[E0539]: malformed `cfg` attribute input
--> $DIR/tokenstream-ice-issue-149954.rs:10:36
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| ^^^^^^
| |
| expected this to be a list
| help: must be of the form: `#[cfg(predicate)]`
|
= note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>

error[E0539]: malformed `cfg` attribute input
--> $DIR/tokenstream-ice-issue-149954.rs:10:36
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| ^^^^^^
| |
| expected this to be a list
| help: must be of the form: `#[cfg(predicate)]`
|
= note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0404]: expected trait, found struct `A`
--> $DIR/tokenstream-ice-issue-149954.rs:10:16
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| ________________^
... |
LL | | >;
| |_________^ not a trait

error[E0404]: expected trait, found type parameter `A`
--> $DIR/tokenstream-ice-issue-149954.rs:10:32
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| - ^^^^^^^^^^^^^^^^ not a trait
| |
| found this type parameter

error[E0404]: expected trait, found struct `A`
--> $DIR/tokenstream-ice-issue-149954.rs:10:16
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| ________________^
... |
LL | | >;
| |_________^ not a trait
|
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0404]: expected trait, found type parameter `A`
--> $DIR/tokenstream-ice-issue-149954.rs:10:32
|
LL | A: A<{ struct A<A: A<{ #[cfg] () }>> ; enum A }
| - ^^^^^^^^^^^^^^^^ not a trait
| |
| found this type parameter
|
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0601]: `main` function not found in crate `tokenstream_ice_issue_149954`
--> $DIR/tokenstream-ice-issue-149954.rs:22:3
|
LL | };
| ^ consider adding a `main` function to `$DIR/tokenstream-ice-issue-149954.rs`

error: aborting due to 11 previous errors

Some errors have detailed explanations: E0404, E0539, E0601.
For more information about an error, try `rustc --explain E0404`.
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