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Auto merge of rust-lang#117292 - estebank:issue-80446, r=davidtwco
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Detect misparsed binop caused by missing semi

When encountering

```rust
foo()
*bar = baz;
```

We currently emit potentially two errors, one for the return type of
`foo` not being multiplicative by the type of `bar`, and another for
`foo() * bar` not being assignable.

We now check for this case and suggest adding a semicolon in the right
place and emit only a single error.

Fix rust-lang#80446.
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bors committed Nov 6, 2023
2 parents aea82b2 + 4b7aaca commit fb61292
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27 changes: 27 additions & 0 deletions compiler/rustc_hir_typeck/src/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -959,12 +959,39 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
Applicability::MachineApplicable,
);
});
self.check_for_missing_semi(lhs, &mut err);

adjust_err(&mut err);

err.emit();
}

/// Check if the expression that could not be assigned to was a typoed expression that
pub fn check_for_missing_semi(
&self,
expr: &'tcx hir::Expr<'tcx>,
err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
) -> bool {
if let hir::ExprKind::Binary(binop, lhs, rhs) = expr.kind
&& let hir::BinOpKind::Mul = binop.node
&& self.tcx.sess.source_map().is_multiline(lhs.span.between(rhs.span))
&& rhs.is_syntactic_place_expr()
{
// v missing semicolon here
// foo()
// *bar = baz;
// (#80446).
err.span_suggestion_verbose(
lhs.span.shrink_to_hi(),
"you might have meant to write a semicolon here",
";".to_string(),
Applicability::MachineApplicable,
);
return true;
}
false
}

// Check if an expression `original_expr_id` comes from the condition of a while loop,
/// as opposed from the body of a while loop, which we can naively check by iterating
/// parents until we find a loop...
Expand Down
7 changes: 7 additions & 0 deletions compiler/rustc_hir_typeck/src/op.rs
Original file line number Diff line number Diff line change
Expand Up @@ -379,6 +379,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
(err, output_def_id)
}
};
if self.check_for_missing_semi(expr, &mut err)
&& let hir::Node::Expr(expr) = self.tcx.hir().get_parent(expr.hir_id)
&& let hir::ExprKind::Assign(..) = expr.kind
{
// We defer to the later error produced by `check_lhs_assignable`.
err.delay_as_bug();
}

let suggest_deref_binop =
|err: &mut DiagnosticBuilder<'_, _>, lhs_deref_ty: Ty<'tcx>| {
Expand Down
10 changes: 10 additions & 0 deletions tests/ui/binop/false-binop-caused-by-missing-semi.fixed
Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
// run-rustfix
fn foo() {}
fn main() {
let mut y = 42;
let x = &mut y;
foo();
*x = 0; //~ ERROR invalid left-hand side of assignment
let _ = x;
println!("{y}");
}
10 changes: 10 additions & 0 deletions tests/ui/binop/false-binop-caused-by-missing-semi.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
// run-rustfix
fn foo() {}
fn main() {
let mut y = 42;
let x = &mut y;
foo()
*x = 0; //~ ERROR invalid left-hand side of assignment
let _ = x;
println!("{y}");
}
17 changes: 17 additions & 0 deletions tests/ui/binop/false-binop-caused-by-missing-semi.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
error[E0070]: invalid left-hand side of assignment
--> $DIR/false-binop-caused-by-missing-semi.rs:7:8
|
LL | / foo()
LL | | *x = 0;
| | - ^
| |______|
| cannot assign to this expression
|
help: you might have meant to write a semicolon here
|
LL | foo();
| +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0070`.

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