Print parens around type assertions for decorators (#3329)

src/fast-path.js

@@ -322,6 +322,12 @@ FastPath.prototype.needsParens = function(options) {
             (node.type === "TSTypeAssertionExpression" ||
               node.type === "TSAsExpression")
           );
+        case "Decorator":
+          return (
+            parent.expression === node &&
+            (node.type === "TSTypeAssertionExpression" ||
+              node.type === "TSAsExpression")
+          );
 
         case "BinaryExpression":
         case "LogicalExpression": {

tests/typescript_decorators/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,24 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`decorator-type-assertion.ts 1`] = `
+@(bind as ClassDecorator)
+class Decorated {
+
+}
+
+@(<ClassDecorator>bind)
+class Decorated {
+
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+@(bind as ClassDecorator)
+class Decorated {}
+
+@(<ClassDecorator>bind)
+class Decorated {}
+
+`;
+
 exports[`decorators.js 1`] = `
 export class TestTextFileService {
 	constructor(

tests/typescript_decorators/decorator-type-assertion.ts

@@ -0,0 +1,9 @@
+@(bind as ClassDecorator)
+class Decorated {
+
+}
+
+@(<ClassDecorator>bind)
+class Decorated {
+
+}