Preserve parens with keyof, enforce parens with arrows with type params (#2503)

* Force parens around argument of simple arrow function if type annotation is present

* Preserve parens inside keyof operator

jest.config.js

@@ -8,7 +8,7 @@ module.exports = {
   testRegex: "jsfmt\\.spec\\.js$|__tests__/.*\\.js$",
   testPathIgnorePatterns: ["tests/new_react", "tests/more_react"],
   collectCoverage: ENABLE_COVERAGE,
-  collectCoverageFrom: ["src/**/*.js", "index.js"],
+  collectCoverageFrom: ["src/**/*.js", "index.js", "!<rootDir>/node_modules/"],
   coveragePathIgnorePatterns: [
     "<rootDir>/src/doc-debug.js",
     "<rootDir>/src/clean-ast.js",

src/fast-path.js

@@ -346,13 +346,15 @@ FastPath.prototype.needsParens = function(options) {
       }
 
     case "TSParenthesizedType": {
+      const grandParent = this.getParentNode(1);
       if (
         (parent.type === "TypeParameter" ||
           parent.type === "VariableDeclarator" ||
           parent.type === "TypeAnnotation" ||
           parent.type === "GenericTypeAnnotation") &&
         (node.typeAnnotation.type === "TypeAnnotation" &&
-          node.typeAnnotation.typeAnnotation.type !== "TSFunctionType")
+          node.typeAnnotation.typeAnnotation.type !== "TSFunctionType" &&
+          grandParent.type !== "TSTypeOperator")
       ) {
         return false;
       }

src/printer.js

@@ -3126,6 +3126,7 @@ function canPrintParamsWithoutParens(node) {
   return (
     node.params.length === 1 &&
     !node.rest &&
+    !node.typeParameters &&
     node.params[0].type === "Identifier" &&
     !node.params[0].typeAnnotation &&
     !node.params[0].comments &&

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

@@ -379,3 +379,10 @@ const initializeSnapshotState = (
 ) => new SnapshotState(testFile, update, testPath, expand);
 
 `;
+
+exports[`type_params.js 1`] = `
+<T>(a) => { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+<T>(a) => {};
+
+`;

tests/arrows/type_params.js

@@ -0,0 +1 @@
+<T>(a) => { }

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

@@ -0,0 +1,15 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`keyof.ts 1`] = `
+type A = keyof (T | U);
+type B = keyof (X & Y);
+type C = keyof T | U;
+type D = keyof X & Y;
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type A = keyof (T | U);
+type B = keyof (X & Y);
+type C = keyof T | U;
+type D = keyof X & Y;
+
+`;

tests/typescript_keyof/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, { parser: "typescript" });

tests/typescript_keyof/keyof.ts

@@ -0,0 +1,5 @@
+type A = keyof (T | U);
+type B = keyof (X & Y);
+type C = keyof T | U;
+type D = keyof X & Y;
+