58982 fix incorrect error diagnostic

src/librustc_typeck/check/coercion.rs

@@ -1224,17 +1224,21 @@ impl<'gcx, 'tcx, 'exprs, E> CoerceMany<'gcx, 'tcx, 'exprs, E>
                             cause.span,
                             blk_id,
                         );
-                        if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
-                            if !sp.overlaps(cause.span) {
-                                db.span_label(*sp, reason_label);
+                        if let ty::Infer(..) = self.expected_ty.sty {
+                            if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
+                                if !sp.overlaps(cause.span) {
+                                    db.span_label(*sp, reason_label);
+                                }
                             }
                         }
                     }
                     _ => {
                         db = fcx.report_mismatched_types(cause, expected, found, err);
-                        if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
-                            if !sp.overlaps(cause.span) {
-                                db.span_label(*sp, reason_label);
+                        if let ty::Infer(..) = self.expected_ty.sty {
+                            if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
+                                if !sp.overlaps(cause.span) {
+                                    db.span_label(*sp, reason_label);
+                                }
                             }
                         }
                     }

src/test/ui/liveness/liveness-forgot-ret.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/liveness-forgot-ret.rs:3:19
    |
 LL | fn f(a: isize) -> isize { if god_exists(a) { return 5; }; }
-   |    -              ^^^^^ expected isize, found ()    - expected because of this statement
+   |    -              ^^^^^ expected isize, found ()
    |    |
    |    this function's body doesn't return
    |