BinOpAssign always returns unit

compiler/rustc_hir_typeck/src/op.rs

@@ -34,19 +34,14 @@ pub(crate) fn check_expr_assign_op(
         rhs: &'tcx Expr<'tcx>,
         expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
-        let (lhs_ty, rhs_ty, return_ty) =
+        let (lhs_ty, rhs_ty, _return_ty) =
             self.check_overloaded_binop(expr, lhs, rhs, Op::AssignOp(op), expected);
 
         let category = BinOpCategory::from(op.node);
-        let ty = if !lhs_ty.is_ty_var()
-            && !rhs_ty.is_ty_var()
-            && is_builtin_binop(lhs_ty, rhs_ty, category)
+        if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, category)
         {
             self.enforce_builtin_binop_types(lhs.span, lhs_ty, rhs.span, rhs_ty, category);
-            self.tcx.types.unit
-        } else {
-            return_ty
-        };
+        }
 
         self.check_lhs_assignable(lhs, E0067, op.span, |err| {
             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
@@ -86,7 +81,7 @@ pub(crate) fn check_expr_assign_op(
             }
         });
 
-        ty
+        self.tcx.types.unit
     }
 
     /// Checks a potentially overloaded binary operator.

tests/ui/parser/let-chains-assign-add-incorrect.fixed

@@ -15,6 +15,8 @@ fn test_where_left_is_not_let() {
     //~| ERROR binary assignment operation `+=` cannot be used in a let chain
     //~| NOTE cannot use `+=` in a let chain
     //~| HELP you might have meant to compare with `==` instead of assigning with `+=`
+    //~| ERROR mismatched types
+    //~| NOTE expected `bool`, found `()`
 }
 
 fn test_where_left_is_let() {
@@ -28,6 +30,8 @@ fn test_where_left_is_let() {
     //~| ERROR binary assignment operation `+=` cannot be used in a let chain
     //~| NOTE cannot use `+=` in a let chain
     //~| HELP you might have meant to compare with `==` instead of assigning with `+=`
+    //~| ERROR mismatched types
+    //~| NOTE expected `bool`, found `()`
 }
 
 fn main() {

tests/ui/parser/let-chains-assign-add-incorrect.rs

@@ -15,6 +15,8 @@ fn test_where_left_is_not_let() {
     //~| ERROR binary assignment operation `+=` cannot be used in a let chain
     //~| NOTE cannot use `+=` in a let chain
     //~| HELP you might have meant to compare with `==` instead of assigning with `+=`
+    //~| ERROR mismatched types
+    //~| NOTE expected `bool`, found `()`
 }
 
 fn test_where_left_is_let() {
@@ -28,6 +30,8 @@ fn test_where_left_is_let() {
     //~| ERROR binary assignment operation `+=` cannot be used in a let chain
     //~| NOTE cannot use `+=` in a let chain
     //~| HELP you might have meant to compare with `==` instead of assigning with `+=`
+    //~| ERROR mismatched types
+    //~| NOTE expected `bool`, found `()`
 }
 
 fn main() {

tests/ui/parser/let-chains-assign-add-incorrect.stderr

@@ -7,7 +7,7 @@ LL |     if let _ = 1 && true && y += 2 {};
    = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
-  --> $DIR/let-chains-assign-add-incorrect.rs:22:8
+  --> $DIR/let-chains-assign-add-incorrect.rs:24:8
    |
 LL |     if let _ = 1 && y += 2 {};
    |        ^^^^^^^^^
@@ -37,13 +37,19 @@ LL +     if let _ = 1 && true && y == 2 {};
    |
 
 error[E0308]: mismatched types
-  --> $DIR/let-chains-assign-add-incorrect.rs:22:21
+  --> $DIR/let-chains-assign-add-incorrect.rs:8:8
+   |
+LL |     if let _ = 1 && true && y += 2 {};
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
+
+error[E0308]: mismatched types
+  --> $DIR/let-chains-assign-add-incorrect.rs:24:21
    |
 LL |     if let _ = 1 && y += 2 {};
    |                     ^ expected `bool`, found integer
 
 error: binary assignment operation `+=` cannot be used in a let chain
-  --> $DIR/let-chains-assign-add-incorrect.rs:22:23
+  --> $DIR/let-chains-assign-add-incorrect.rs:24:23
    |
 LL |     if let _ = 1 && y += 2 {};
    |        -------------- ^^ cannot use `+=` in a let chain
@@ -56,6 +62,12 @@ LL -     if let _ = 1 && y += 2 {};
 LL +     if let _ = 1 && y == 2 {};
    |
 
-error: aborting due to 6 previous errors
+error[E0308]: mismatched types
+  --> $DIR/let-chains-assign-add-incorrect.rs:24:8
+   |
+LL |     if let _ = 1 && y += 2 {};
+   |        ^^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
+
+error: aborting due to 8 previous errors
 
 For more information about this error, try `rustc --explain E0308`.