Only suppress binop error in favor of semicolon suggestion if we're in an assignment statement

compiler/rustc_hir_typeck/src/op.rs

@@ -381,10 +381,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  let maybe_missing_semi = self.check_for_missing_semi(expr, &mut err);
 
  // We defer to the later error produced by `check_lhs_assignable`.
- // We only downgrade this if it's the LHS, though.
+ // We only downgrade this if it's the LHS, though, and if this is a
+ // valid assignment statement.
  if maybe_missing_semi
  && let hir::Node::Expr(parent) = self.tcx.parent_hir_node(expr.hir_id)
  && let hir::ExprKind::Assign(lhs, _, _) = parent.kind
+ && let hir::Node::Stmt(stmt) = self.tcx.parent_hir_node(parent.hir_id)
+ && let hir::StmtKind::Expr(_) | hir::StmtKind::Semi(_) = stmt.kind
  && lhs.hir_id == expr.hir_id
  {
  err.downgrade_to_delayed_bug();

tests/ui/binop/nested-assignment-may-be-deref.rs

@@ -0,0 +1,14 @@
+pub fn bad(x: &mut bool) {
+ if true
+ *x = true {}
+ //~^ ERROR cannot multiply `bool` by `&mut bool`
+}
+
+pub fn bad2(x: &mut bool) {
+ let y: bool;
+ y = true
+ *x = true;
+ //~^ ERROR cannot multiply `bool` by `&mut bool`
+}
+
+fn main() {}

tests/ui/binop/nested-assignment-may-be-deref.stderr

@@ -0,0 +1,29 @@
+error[E0369]: cannot multiply `bool` by `&mut bool`
+ --> $DIR/nested-assignment-may-be-deref.rs:3:5
+ |
+LL | if true
+ | ---- bool
+LL | *x = true {}
+ | ^- &mut bool
+ |
+help: you might have meant to write a semicolon here
+ |
+LL | if true;
+ | +
+
+error[E0369]: cannot multiply `bool` by `&mut bool`
+ --> $DIR/nested-assignment-may-be-deref.rs:10:5
+ |
+LL | y = true
+ | ---- bool
+LL | *x = true;
+ | ^- &mut bool
+ |
+help: you might have meant to write a semicolon here
+ |
+LL | y = true;
+ | +
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0369`.