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Suggest parentheses when match or if expression in binop is parsed as statement #146044

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Merged
merged 3 commits into from
Sep 5, 2025
Merged

Suggest parentheses when match or if expression in binop is parsed as statement #146044

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a7e32a5
Provide suggestion when encountering `match () { () => 1 } + match ()…
estebank Aug 31, 2025
f5b5e67
More targeted parentheses suggestion for match statement intended as …
estebank Aug 31, 2025
ff60e5c
Suggest parentheses around if-expressions
estebank Sep 2, 2025
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2 changes: 1 addition & 1 deletion compiler/rustc_hir_typeck/src/coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1897,7 +1897,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
fcx.suggest_semicolon_at_end(cond_expr.span, &mut err);
}
}
};
}
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do we have a style lint to check this?

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Don't think we do.


// If this is due to an explicit `return`, suggest adding a return type.
if let Some((fn_id, fn_decl)) = fcx.get_fn_decl(block_or_return_id)
Expand Down
17 changes: 16 additions & 1 deletion compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
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Expand Up @@ -1912,7 +1912,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
hir::StmtKind::Expr(ref expr) => {
// Check with expected type of `()`.
self.check_expr_has_type_or_error(expr, self.tcx.types.unit, |err| {
if expr.can_have_side_effects() {
if self.is_next_stmt_expr_continuation(stmt.hir_id)
&& let hir::ExprKind::Match(..) | hir::ExprKind::If(..) = expr.kind
{
// We have something like `match () { _ => true } && true`. Suggest
// wrapping in parentheses. We find the statement or expression
// following the `match` (`&& true`) and see if it is something that
// can reasonably be interpreted as a binop following an expression.
err.multipart_suggestion(
"parentheses are required to parse this as an expression",
vec![
(expr.span.shrink_to_lo(), "(".to_string()),
(expr.span.shrink_to_hi(), ")".to_string()),
],
Applicability::MachineApplicable,
);
} else if expr.can_have_side_effects() {
self.suggest_semicolon_at_end(expr.span, err);
}
});
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146 changes: 106 additions & 40 deletions compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
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@@ -1,3 +1,4 @@
// ignore-tidy-filelength
use core::cmp::min;
use core::iter;

Expand Down Expand Up @@ -766,56 +767,121 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
needs_block: bool,
parent_is_closure: bool,
) {
if expected.is_unit() {
// `BlockTailExpression` only relevant if the tail expr would be
// useful on its own.
match expression.kind {
ExprKind::Call(..)
| ExprKind::MethodCall(..)
| ExprKind::Loop(..)
| ExprKind::If(..)
| ExprKind::Match(..)
| ExprKind::Block(..)
if expression.can_have_side_effects()
// If the expression is from an external macro, then do not suggest
// adding a semicolon, because there's nowhere to put it.
// See issue #81943.
&& !expression.span.in_external_macro(self.tcx.sess.source_map()) =>
if !expected.is_unit() {
return;
}
// `BlockTailExpression` only relevant if the tail expr would be
// useful on its own.
match expression.kind {
ExprKind::Call(..)
| ExprKind::MethodCall(..)
| ExprKind::Loop(..)
| ExprKind::If(..)
| ExprKind::Match(..)
| ExprKind::Block(..)
if expression.can_have_side_effects()
// If the expression is from an external macro, then do not suggest
// adding a semicolon, because there's nowhere to put it.
// See issue #81943.
&& !expression.span.in_external_macro(self.tcx.sess.source_map()) =>
{
if needs_block {
err.multipart_suggestion(
"consider using a semicolon here",
vec![
(expression.span.shrink_to_lo(), "{ ".to_owned()),
(expression.span.shrink_to_hi(), "; }".to_owned()),
],
Applicability::MachineApplicable,
);
} else if let hir::Node::Block(block) = self.tcx.parent_hir_node(expression.hir_id)
&& let hir::Node::Expr(expr) = self.tcx.parent_hir_node(block.hir_id)
&& let hir::Node::Expr(if_expr) = self.tcx.parent_hir_node(expr.hir_id)
&& let hir::ExprKind::If(_cond, _then, Some(_else)) = if_expr.kind
&& let hir::Node::Stmt(stmt) = self.tcx.parent_hir_node(if_expr.hir_id)
&& let hir::StmtKind::Expr(_) = stmt.kind
&& self.is_next_stmt_expr_continuation(stmt.hir_id)
{
if needs_block {
err.multipart_suggestion(
"consider using a semicolon here",
vec![
(expression.span.shrink_to_lo(), "{ ".to_owned()),
(expression.span.shrink_to_hi(), "; }".to_owned()),
],
Applicability::MachineApplicable,
);
} else {
err.span_suggestion(
expression.span.shrink_to_hi(),
"consider using a semicolon here",
";",
Applicability::MachineApplicable,
);
}
err.multipart_suggestion(
"parentheses are required to parse this as an expression",
vec![
(stmt.span.shrink_to_lo(), "(".to_string()),
(stmt.span.shrink_to_hi(), ")".to_string()),
],
Applicability::MachineApplicable,
);
} else {
err.span_suggestion(
expression.span.shrink_to_hi(),
"consider using a semicolon here",
";",
Applicability::MachineApplicable,
);
}
ExprKind::Path(..) | ExprKind::Lit(_)
if parent_is_closure
&& !expression.span.in_external_macro(self.tcx.sess.source_map()) =>
}
ExprKind::Path(..) | ExprKind::Lit(_)
if parent_is_closure
&& !expression.span.in_external_macro(self.tcx.sess.source_map()) =>
{
err.span_suggestion_verbose(
expression.span.shrink_to_lo(),
"consider ignoring the value",
"_ = ",
Applicability::MachineApplicable,
);
}
_ => {
if let hir::Node::Block(block) = self.tcx.parent_hir_node(expression.hir_id)
&& let hir::Node::Expr(expr) = self.tcx.parent_hir_node(block.hir_id)
&& let hir::Node::Expr(if_expr) = self.tcx.parent_hir_node(expr.hir_id)
&& let hir::ExprKind::If(_cond, _then, Some(_else)) = if_expr.kind
&& let hir::Node::Stmt(stmt) = self.tcx.parent_hir_node(if_expr.hir_id)
&& let hir::StmtKind::Expr(_) = stmt.kind
&& self.is_next_stmt_expr_continuation(stmt.hir_id)
{
err.span_suggestion_verbose(
expression.span.shrink_to_lo(),
"consider ignoring the value",
"_ = ",
// The error is pointing at an arm of an if-expression, and we want to get the
// `Span` of the whole if-expression for the suggestion. This only works for a
// single level of nesting, which is fine.
// We have something like `if true { false } else { true } && true`. Suggest
// wrapping in parentheses. We find the statement or expression following the
// `if` (`&& true`) and see if it is something that can reasonably be
// interpreted as a binop following an expression.
err.multipart_suggestion(
"parentheses are required to parse this as an expression",
vec![
(stmt.span.shrink_to_lo(), "(".to_string()),
(stmt.span.shrink_to_hi(), ")".to_string()),
],
Applicability::MachineApplicable,
);
}
_ => (),
}
}
}

pub(crate) fn is_next_stmt_expr_continuation(&self, hir_id: HirId) -> bool {
if let hir::Node::Block(b) = self.tcx.parent_hir_node(hir_id)
&& let mut stmts = b.stmts.iter().skip_while(|s| s.hir_id != hir_id)
&& let Some(_) = stmts.next() // The statement the statement that was passed in
&& let Some(next) = match (stmts.next(), b.expr) { // The following statement
(Some(next), _) => match next.kind {
hir::StmtKind::Expr(next) | hir::StmtKind::Semi(next) => Some(next),
_ => None,
},
(None, Some(next)) => Some(next),
_ => None,
}
&& let hir::ExprKind::AddrOf(..) // prev_stmt && next
| hir::ExprKind::Unary(..) // prev_stmt * next
| hir::ExprKind::Err(_) = next.kind
// prev_stmt + next
{
true
} else {
false
}
}

/// A possible error is to forget to add a return type that is needed:
///
/// ```compile_fail,E0308
Expand Down
23 changes: 22 additions & 1 deletion tests/ui/parser/expr-as-stmt-2.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,4 +7,25 @@ fn foo(a: Option<u32>, b: Option<u32>) -> bool {
if let Some(y) = a { true } else { false }
}

fn main() {}
fn bar() -> bool {
false
}

fn main() {
if true { true } else { false } && true;
//~^ ERROR mismatched types
//~| ERROR mismatched types
if true { true } else { false } && if true { true } else { false };
//~^ ERROR mismatched types
//~| ERROR mismatched types
if true { true } else { false } if true { true } else { false };
//~^ ERROR mismatched types
//~| ERROR mismatched types
if true { bar() } else { bar() } && if true { bar() } else { bar() };
//~^ ERROR mismatched types
//~| ERROR mismatched types
if true { bar() } else { bar() } if true { bar() } else { bar() };
//~^ ERROR mismatched types
//~| ERROR mismatched types
let _ = if true { true } else { false } && true; // ok
}
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