Silence redundant error on typo resulting on binop

Author: estebank

compiler/rustc_hir_typeck/src/op.rs

@@ -394,6 +394,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         ";".to_string(),
                         Applicability::MaybeIncorrect,
                     );
+                    if 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 =

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}");
+}

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}");
 }

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`.