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Oct 2, 2025
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Merged

Tweak handling of "struct like start" where a struct isn't supported #147004

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4305769
Tweak handling of "struct like start" where a struct isn't supported
estebank Sep 24, 2025
bb48c16
Simplify logic slightly
estebank Sep 24, 2025
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40 changes: 16 additions & 24 deletions compiler/rustc_parse/src/parser/diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2748,28 +2748,7 @@ impl<'a> Parser<'a> {
if token::Colon != self.token.kind {
return first_pat;
}
if !matches!(first_pat.kind, PatKind::Ident(_, _, None) | PatKind::Path(..))
|| !self.look_ahead(1, |token| token.is_non_reserved_ident())
{
let mut snapshot_type = self.create_snapshot_for_diagnostic();
snapshot_type.bump(); // `:`
match snapshot_type.parse_ty() {
Err(inner_err) => {
inner_err.cancel();
}
Ok(ty) => {
let Err(mut err) = self.expected_one_of_not_found(&[], &[]) else {
return first_pat;
};
err.span_label(ty.span, "specifying the type of a pattern isn't supported");
self.restore_snapshot(snapshot_type);
let span = first_pat.span.to(ty.span);
first_pat = self.mk_pat(span, PatKind::Wild);
err.emit();
}
}
return first_pat;
}

// The pattern looks like it might be a path with a `::` -> `:` typo:
// `match foo { bar:baz => {} }`
let colon_span = self.token.span;
Expand Down Expand Up @@ -2857,7 +2836,13 @@ impl<'a> Parser<'a> {
Applicability::MaybeIncorrect,
);
} else {
first_pat = self.mk_pat(new_span, PatKind::Wild);
first_pat = self.mk_pat(
new_span,
PatKind::Err(
self.dcx()
.span_delayed_bug(colon_span, "recovered bad path pattern"),
),
);
}
self.restore_snapshot(snapshot_pat);
}
Expand All @@ -2870,7 +2855,14 @@ impl<'a> Parser<'a> {
err.span_label(ty.span, "specifying the type of a pattern isn't supported");
self.restore_snapshot(snapshot_type);
let new_span = first_pat.span.to(ty.span);
first_pat = self.mk_pat(new_span, PatKind::Wild);
first_pat =
self.mk_pat(
new_span,
PatKind::Err(self.dcx().span_delayed_bug(
colon_span,
"recovered bad pattern with type",
)),
);
}
}
err.emit();
Expand Down
58 changes: 42 additions & 16 deletions compiler/rustc_parse/src/parser/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3612,7 +3612,7 @@ impl<'a> Parser<'a> {
self.token.is_keyword(kw::Async) && self.is_gen_block(kw::Gen, 1)
}

fn is_certainly_not_a_block(&self) -> bool {
fn is_likely_struct_lit(&self) -> bool {
// `{ ident, ` and `{ ident: ` cannot start a block.
self.look_ahead(1, |t| t.is_ident())
&& self.look_ahead(2, |t| t == &token::Comma || t == &token::Colon)
Expand All @@ -3624,24 +3624,50 @@ impl<'a> Parser<'a> {
path: &ast::Path,
) -> Option<PResult<'a, Box<Expr>>> {
let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
if struct_allowed || self.is_certainly_not_a_block() {
if let Err(err) = self.expect(exp!(OpenBrace)) {
return Some(Err(err));
match (struct_allowed, self.is_likely_struct_lit()) {
// A struct literal isn't expected and one is pretty much assured not to be present. The
// only situation that isn't detected is when a struct with a single field was attempted
// in a place where a struct literal wasn't expected, but regular parser errors apply.
// Happy path.
(false, false) => None,
(true, _) => {
// A struct is accepted here, try to parse it and rely on `parse_expr_struct` for
// any kind of recovery. Happy path.
if let Err(err) = self.expect(exp!(OpenBrace)) {
return Some(Err(err));
}
Some(self.parse_expr_struct(qself.clone(), path.clone(), true))
}
let expr = self.parse_expr_struct(qself.clone(), path.clone(), true);
if let (Ok(expr), false) = (&expr, struct_allowed) {
// This is a struct literal, but we don't can't accept them here.
self.dcx().emit_err(errors::StructLiteralNotAllowedHere {
span: expr.span,
sub: errors::StructLiteralNotAllowedHereSugg {
left: path.span.shrink_to_lo(),
right: expr.span.shrink_to_hi(),
},
});
(false, true) => {
// We have something like `match foo { bar,` or `match foo { bar:`, which means the
// user might have meant to write a struct literal as part of the `match`
// discriminant. This is done purely for error recovery.
let snapshot = self.create_snapshot_for_diagnostic();
if let Err(err) = self.expect(exp!(OpenBrace)) {
return Some(Err(err));
}
match self.parse_expr_struct(qself.clone(), path.clone(), false) {
Ok(expr) => {
// This is a struct literal, but we don't accept them here.
self.dcx().emit_err(errors::StructLiteralNotAllowedHere {
span: expr.span,
sub: errors::StructLiteralNotAllowedHereSugg {
left: path.span.shrink_to_lo(),
right: expr.span.shrink_to_hi(),
},
});
Some(Ok(expr))
}
Err(err) => {
// We couldn't parse a valid struct, rollback and let the parser emit an
// error elsewhere.
err.cancel();
self.restore_snapshot(snapshot);
None
}
}
}
return Some(expr);
}
None
}

pub(super) fn parse_struct_fields(
Expand Down
3 changes: 1 addition & 2 deletions tests/ui/parser/issues/issue-87086-colon-path-sep.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,10 +37,9 @@ fn g1() {
//~| HELP: maybe write a path separator here
_ => {}
}
if let Foo:Bar = f() { //~ WARN: irrefutable `if let` pattern
if let Foo:Bar = f() {
//~^ ERROR: expected one of
//~| HELP: maybe write a path separator here
//~| HELP: consider replacing the `if let` with a `let`
}
}

Expand Down
20 changes: 5 additions & 15 deletions tests/ui/parser/issues/issue-87086-colon-path-sep.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,7 @@ LL | if let Foo::Bar = f() {
| +

error: expected one of `@` or `|`, found `:`
--> $DIR/issue-87086-colon-path-sep.rs:49:16
--> $DIR/issue-87086-colon-path-sep.rs:48:16
|
LL | ref qux: Foo::Baz => {}
| ^ -------- specifying the type of a pattern isn't supported
Expand All @@ -77,7 +77,7 @@ LL | ref qux::Foo::Baz => {}
| ~~

error: expected one of `@` or `|`, found `:`
--> $DIR/issue-87086-colon-path-sep.rs:58:16
--> $DIR/issue-87086-colon-path-sep.rs:57:16
|
LL | mut qux: Foo::Baz => {}
| ^ -------- specifying the type of a pattern isn't supported
Expand All @@ -90,7 +90,7 @@ LL | mut qux::Foo::Baz => {}
| ~~

error: expected one of `@` or `|`, found `:`
--> $DIR/issue-87086-colon-path-sep.rs:69:12
--> $DIR/issue-87086-colon-path-sep.rs:68:12
|
LL | Foo:Bar::Baz => {}
| ^-------- specifying the type of a pattern isn't supported
Expand All @@ -103,7 +103,7 @@ LL | Foo::Bar::Baz => {}
| +

error: expected one of `@` or `|`, found `:`
--> $DIR/issue-87086-colon-path-sep.rs:75:12
--> $DIR/issue-87086-colon-path-sep.rs:74:12
|
LL | Foo:Bar => {}
| ^--- specifying the type of a pattern isn't supported
Expand All @@ -115,15 +115,5 @@ help: maybe write a path separator here
LL | Foo::Bar => {}
| +

warning: irrefutable `if let` pattern
--> $DIR/issue-87086-colon-path-sep.rs:40:8
|
LL | if let Foo:Bar = f() {
| ^^^^^^^^^^^^^^^^^
|
= note: this pattern will always match, so the `if let` is useless
= help: consider replacing the `if let` with a `let`
= note: `#[warn(irrefutable_let_patterns)]` on by default

error: aborting due to 9 previous errors; 1 warning emitted
error: aborting due to 9 previous errors

17 changes: 9 additions & 8 deletions tests/ui/parser/type-ascription-in-pattern.rs
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Original file line number Diff line number Diff line change
@@ -1,15 +1,16 @@
fn foo(x: bool) -> i32 {
match x { //~ ERROR struct literals are not allowed here
x: i32 => x, //~ ERROR expected
true => 42., //~ ERROR expected identifier
false => 0.333, //~ ERROR expected identifier
match x {
x: i32 => x, //~ ERROR: expected
//~^ ERROR: mismatched types
true => 42.,
false => 0.333,
}
} //~ ERROR expected one of
}

fn main() {
match foo(true) {
42: i32 => (), //~ ERROR expected
_: f64 => (), //~ ERROR expected
x: i32 => (), //~ ERROR expected
42: i32 => (), //~ ERROR: expected
_: f64 => (), //~ ERROR: expected
x: i32 => (), //~ ERROR: expected
}
}
80 changes: 22 additions & 58 deletions tests/ui/parser/type-ascription-in-pattern.stderr
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Original file line number Diff line number Diff line change
@@ -1,80 +1,34 @@
error: expected one of `!`, `,`, `.`, `::`, `?`, `{`, `}`, or an operator, found `=>`
--> $DIR/type-ascription-in-pattern.rs:3:16
|
LL | match x {
| - while parsing this struct
LL | x: i32 => x,
| -^^ expected one of 8 possible tokens
| |
| help: try adding a comma: `,`

error: expected identifier, found keyword `true`
--> $DIR/type-ascription-in-pattern.rs:4:9
|
LL | match x {
| - while parsing this struct
LL | x: i32 => x,
LL | true => 42.,
| ^^^^ expected identifier, found keyword

error: expected identifier, found keyword `false`
--> $DIR/type-ascription-in-pattern.rs:5:9
|
LL | match x {
| - while parsing this struct
...
LL | false => 0.333,
| ^^^^^ expected identifier, found keyword

error: struct literals are not allowed here
--> $DIR/type-ascription-in-pattern.rs:2:11
|
LL | match x {
| ___________^
LL | | x: i32 => x,
LL | | true => 42.,
LL | | false => 0.333,
LL | | }
| |_____^
|
help: surround the struct literal with parentheses
error: expected one of `@` or `|`, found `:`
--> $DIR/type-ascription-in-pattern.rs:3:10
|
LL ~ match (x {
LL | x: i32 => x,
LL | true => 42.,
LL | false => 0.333,
LL ~ })
| ^ --- specifying the type of a pattern isn't supported
| |
| expected one of `@` or `|`
|

error: expected one of `.`, `?`, `{`, or an operator, found `}`
--> $DIR/type-ascription-in-pattern.rs:7:1
help: maybe write a path separator here
|
LL | match x {
| ----- while parsing this `match` expression
...
LL | }
| - expected one of `.`, `?`, `{`, or an operator
LL | }
| ^ unexpected token
LL | x::i32 => x,
| ~~

error: expected one of `...`, `..=`, `..`, or `|`, found `:`
--> $DIR/type-ascription-in-pattern.rs:11:11
--> $DIR/type-ascription-in-pattern.rs:12:11
|
LL | 42: i32 => (),
| ^ --- specifying the type of a pattern isn't supported
| |
| expected one of `...`, `..=`, `..`, or `|`

error: expected `|`, found `:`
--> $DIR/type-ascription-in-pattern.rs:12:10
--> $DIR/type-ascription-in-pattern.rs:13:10
|
LL | _: f64 => (),
| ^ --- specifying the type of a pattern isn't supported
| |
| expected `|`

error: expected one of `@` or `|`, found `:`
--> $DIR/type-ascription-in-pattern.rs:13:10
--> $DIR/type-ascription-in-pattern.rs:14:10
|
LL | x: i32 => (),
| ^ --- specifying the type of a pattern isn't supported
Expand All @@ -86,5 +40,15 @@ help: maybe write a path separator here
LL | x::i32 => (),
| ~~

error: aborting due to 8 previous errors
error[E0308]: mismatched types
--> $DIR/type-ascription-in-pattern.rs:3:19
|
LL | fn foo(x: bool) -> i32 {
| --- expected `i32` because of return type
LL | match x {
LL | x: i32 => x,
| ^ expected `i32`, found `bool`

error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0308`.
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