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Remove incorrect parse error recovery code that mistakes as casts for the long removed type ascription #162700

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Remove incorrect parse error recovery code that mistakes as casts for the long removed type ascription #162700

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4b98f77
Remove incorrect parse error recovery code that mistakes `as` casts f…
fmease Sep 12, 2026
f97a732
Further simplify `parse_assoc_op_cast`
fmease Sep 12, 2026
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111 changes: 36 additions & 75 deletions compiler/rustc_parse/src/parser/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -261,7 +261,7 @@ impl<'a> Parser<'a> {
let op = op.node;
// Special cases:
if op == AssocOp::Cast {
lhs = self.parse_assoc_op_cast(lhs, lhs_span, op_span, ExprKind::Cast)?;
lhs = self.parse_assoc_op_cast(lhs, lhs_span, op_span)?;
continue;
} else if let AssocOp::Range(limits) = op {
// If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
Expand Down Expand Up @@ -645,17 +645,17 @@ impl<'a> Parser<'a> {
lhs: Box<Expr>,
lhs_span: Span,
op_span: Span,
expr_kind: fn(Box<Expr>, Box<Ty>) -> ExprKind,
) -> PResult<'a, Box<Expr>> {
let mk_expr = |this: &mut Self, lhs: Box<Expr>, rhs: Box<Ty>| {
this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, op_span, rhs.span), expr_kind(lhs, rhs))
let mk_expr = |this: &mut Self, rhs: Box<Ty>| {
let span = this.mk_expr_sp(&lhs, lhs_span, op_span, rhs.span);
this.mk_expr(span, ExprKind::Cast(lhs, rhs))
};

// Save the state of the parser before parsing type normally, in case there is a
// LessThan comparison after this cast.
let parser_snapshot_before_type = self.clone();
let cast_expr = match self.parse_as_cast_ty() {
Ok(rhs) => mk_expr(self, lhs, rhs),
Ok(rhs) => mk_expr(self, rhs),
Err(type_err) => {
if !self.may_recover() {
return Err(type_err);
Expand All @@ -666,46 +666,11 @@ impl<'a> Parser<'a> {
// `usize < y` as a type with generic arguments.
let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);

// Check for typo of `'a: loop { break 'a }` with a missing `'`.
match (&lhs.kind, &self.token.kind) {
(
// `foo: `
ExprKind::Path(None, ast::Path { segments, .. }),
token::Ident(kw::For | kw::Loop | kw::While, IdentIsRaw::No),
) if let [segment] = segments.as_slice() => {
let snapshot = self.create_snapshot_for_diagnostic();
let label = Label {
ident: Ident::from_str_and_span(
&format!("'{}", segment.ident),
segment.ident.span,
),
};
match self.parse_expr_labeled(label, false) {
Ok(expr) => {
type_err.cancel();
self.dcx().emit_err(diagnostics::MalformedLoopLabel {
span: label.ident.span,
suggestion: label.ident.span.shrink_to_lo(),
});
return Ok(expr);
}
Err(err) => {
err.cancel();
self.restore_snapshot(snapshot);
}
}
}
_ => {}
}

match self.parse_path(PathStyle::Expr) {
Ok(path) => {
let span_after_type = parser_snapshot_after_type.token.span;
let expr = mk_expr(
self,
lhs,
self.mk_ty(path.span, TyKind::Path(None, path.clone())),
);
let expr =
mk_expr(self, self.mk_ty(path.span, TyKind::Path(None, path.clone())));

let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
match self.token.kind {
Expand Down Expand Up @@ -769,42 +734,38 @@ impl<'a> Parser<'a> {
// Check if an illegal postfix operator has been added after the cast.
// If the resulting expression is not a cast, it is an illegal postfix operator.
if !matches!(with_postfix.kind, ExprKind::Cast(_, _)) {
let msg = format!(
"cast cannot be followed by {}",
match with_postfix.kind {
ExprKind::Index(..) => "indexing",
ExprKind::Try(_) => "`?`",
ExprKind::Field(_, _) => "a field access",
ExprKind::MethodCall(_) => "a method call",
ExprKind::Call(_, _) => "a function call",
ExprKind::Await(_, _) => "`.await`",
ExprKind::Use(_, _) => "`.use`",
ExprKind::Yield(YieldKind::Postfix(_)) => "`.yield`",
ExprKind::Match(_, _, MatchKind::Postfix) => "a postfix match",
ExprKind::Err(_) => return Ok(with_postfix),
_ => unreachable!(
"did not expect {:?} as an illegal postfix operator following cast",
with_postfix.kind
self.dcx()
.struct_span_err(
span,
format!(
"cast cannot be followed by {}",
match with_postfix.kind {
ExprKind::Index(..) => "indexing",
ExprKind::Try(_) => "`?`",
ExprKind::Field(_, _) => "a field access",
ExprKind::MethodCall(_) => "a method call",
ExprKind::Call(_, _) => "a function call",
ExprKind::Await(_, _) => "`.await`",
ExprKind::Use(_, _) => "`.use`",
ExprKind::Yield(YieldKind::Postfix(_)) => "`.yield`",
ExprKind::Match(_, _, MatchKind::Postfix) => "a postfix match",
ExprKind::Err(_) => return Ok(with_postfix),
_ => unreachable!(
"did not expect {:?} as an illegal postfix operator following cast",
with_postfix.kind
),
}
),
}
);
let mut err = self.dcx().struct_span_err(span, msg);

let suggest_parens = |err: &mut Diag<'_>| {
let suggestions = vec![
(span.shrink_to_lo(), "(".to_string()),
(span.shrink_to_hi(), ")".to_string()),
];
err.multipart_suggestion(
)
.with_multipart_suggestion(
"try surrounding the expression in parentheses",
suggestions,
vec![
(span.shrink_to_lo(), "(".to_string()),
(span.shrink_to_hi(), ")".to_string()),
],
Applicability::MachineApplicable,
);
};

suggest_parens(&mut err);

err.emit();
)
.emit();
};
Ok(with_postfix)
}
Expand Down
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