Fix export of grouping modifier

promql/printer.go

@@ -176,9 +176,7 @@ func (node *BinaryExpr) String() string {
 			} else {
 				matching += "RIGHT"
 			}
-			if len(vm.Include) > 0 {
-				matching += fmt.Sprintf("(%s)", vm.Include)
-			}
+			matching += fmt.Sprintf("(%s)", vm.Include)
 		}
 	}
 	return fmt.Sprintf("%s %s%s%s %s", node.LHS, node.Op, returnBool, matching, node.RHS)

promql/printer_test.go

@@ -94,7 +94,11 @@ func TestExprString(t *testing.T) {
 			in: `a - ON(b) GROUP_LEFT(x, y) c`,
 		},
 		{
-			in: `a - ON(b) GROUP_LEFT c`,
+			in:  `a - ON(b) GROUP_LEFT c`,
+			out: `a - ON(b) GROUP_LEFT() c`,
+		},
+		{
+			in: `a - ON(b) GROUP_LEFT() (c)`,
 		},
 		{
 			in: `a - IGNORING(b) c`,