Silence redundant error on typo resulting on binop

Author: estebank

Diff for: compiler/rustc_hir_typeck/src/expr.rs

@@ -961,7 +961,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     /// Check if the expression that could not be assigned to was a typoed expression that
-    fn check_for_missing_semi(&self, expr: &'tcx hir::Expr<'tcx>, err: &mut Diagnostic) {
+    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))
@@ -977,7 +981,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ";".to_string(),
                 Applicability::MachineApplicable,
             );
+            return true;
         }
+        false
     }
 
     // Check if an expression `original_expr_id` comes from the condition of a while loop,

Diff for: compiler/rustc_hir_typeck/src/op.rs

@@ -379,21 +379,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         (err, output_def_id)
                     }
                 };
-                if self.tcx.sess.source_map().is_multiline(lhs_expr.span.between(rhs_expr.span))
-                    && let IsAssign::No = is_assign
-                    && let hir::BinOpKind::Mul = op.node
-                    && rhs_expr.is_syntactic_place_expr()
+                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
                 {
-                    //      v missing semicolon here
-                    // foo()
-                    // *bar = baz;
-                    // (#80446).
-                    err.span_suggestion_verbose(
-                        lhs_expr.span.shrink_to_hi(),
-                        "you might have meant to write a semicolon here",
-                        ";".to_string(),
-                        Applicability::MaybeIncorrect,
-                    );
+                    // We defer to the later error produced by `check_lhs_assignable`.
+                    err.delay_as_bug();
                 }
 
                 let suggest_deref_binop =

Diff for: tests/ui/binop/false-binop-caused-by-missing-semi.fixed

@@ -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}");
+}

Diff for: tests/ui/binop/false-binop-caused-by-missing-semi.rs

@@ -1,9 +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
-    //~^ ERROR cannot multiply `()` by `&mut {integer}`
+    let _ = x;
     println!("{y}");
 }

Diff for: tests/ui/binop/false-binop-caused-by-missing-semi.stderr

@@ -1,18 +1,5 @@
-error[E0369]: cannot multiply `()` by `&mut {integer}`
-  --> $DIR/false-binop-caused-by-missing-semi.rs:6:5
-   |
-LL |     foo()
-   |     ----- ()
-LL |     *x = 0;
-   |     ^- &mut {integer}
-   |
-help: you might have meant to write a semicolon here
-   |
-LL |     foo();
-   |          +
-
 error[E0070]: invalid left-hand side of assignment
-  --> $DIR/false-binop-caused-by-missing-semi.rs:6:8
+  --> $DIR/false-binop-caused-by-missing-semi.rs:7:8
    |
 LL | /     foo()
 LL | |     *x = 0;
@@ -25,7 +12,6 @@ help: you might have meant to write a semicolon here
 LL |     foo();
    |          +
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0070, E0369.
-For more information about an error, try `rustc --explain E0070`.
+For more information about this error, try `rustc --explain E0070`.