Add handling parens for extends clause in generator (#6897)

packages/babel-generator/src/node/parentheses.js

@@ -27,6 +27,10 @@ const PRECEDENCE = {
   "**": 10,
 };
 
+const isClassExtendsClause = (node: Object, parent: Object): boolean =>
+  (t.isClassDeclaration(parent) || t.isClassExpression(parent)) &&
+  parent.superClass === node;
+
 export function NullableTypeAnnotation(node: Object, parent: Object): boolean {
   return t.isArrayTypeAnnotation(parent);
 }
@@ -35,7 +39,10 @@ export { NullableTypeAnnotation as FunctionTypeAnnotation };
 
 export function UpdateExpression(node: Object, parent: Object): boolean {
   // (foo++).test()
-  return t.isMemberExpression(parent) && parent.object === node;
+  return (
+    (t.isMemberExpression(parent) && parent.object === node) ||
+    isClassExtendsClause(node, parent)
+  );
 }
 
 export function ObjectExpression(
@@ -62,6 +69,10 @@ export function Binary(node: Object, parent: Object): boolean {
     return parent.left === node;
   }
 
+  if (isClassExtendsClause(node, parent)) {
+    return true;
+  }
+
   if (
     ((t.isCallExpression(parent) || t.isNewExpression(parent)) &&
       parent.callee === node) ||
@@ -151,7 +162,8 @@ export function YieldExpression(node: Object, parent: Object): boolean {
     t.isCallExpression(parent) ||
     t.isMemberExpression(parent) ||
     t.isNewExpression(parent) ||
-    (t.isConditionalExpression(parent) && node === parent.test)
+    (t.isConditionalExpression(parent) && node === parent.test) ||
+    isClassExtendsClause(node, parent)
   );
 }
 
@@ -170,7 +182,8 @@ export function UnaryLike(node: Object, parent: Object): boolean {
     t.isMemberExpression(parent, { object: node }) ||
     t.isCallExpression(parent, { callee: node }) ||
     t.isNewExpression(parent, { callee: node }) ||
-    t.isBinaryExpression(parent, { operator: "**", left: node })
+    t.isBinaryExpression(parent, { operator: "**", left: node }) ||
+    isClassExtendsClause(node, parent)
   );
 }
 
@@ -210,6 +223,10 @@ export function AssignmentExpression(node: Object): boolean {
   }
 }
 
+export function NewExpression(node: Object, parent: Object): boolean {
+  return isClassExtendsClause(node, parent);
+}
+
 // Walk up the print stack to determine if our node can come first
 // in statement.
 function isFirstInStatement(