Always print parentheses around arrow function parameters

packages/babel-generator/src/generators/methods.ts

@@ -110,37 +110,7 @@ export function ArrowFunctionExpression(
     this.space();
   }
 
-  const firstParam = node.params[0];
-
-  if (
-    node.params.length === 1 &&
-    t.isIdentifier(firstParam) &&
-    !hasTypes(node, firstParam)
-  ) {
-    if (
-      (this.format.retainLines || node.async) &&
-      ((node.loc &&
-        node.body.loc &&
-        node.loc.start.line < node.body.loc.start.line) ||
-        firstParam.leadingComments?.length ||
-        firstParam.trailingComments?.length)
-    ) {
-      this.token("(");
-      if (firstParam.loc && firstParam.loc.start.line > node.loc.start.line) {
-        this.indent();
-        this.print(firstParam, node);
-        this.dedent();
-        this._catchUp("start", node.body.loc);
-      } else {
-        this.print(firstParam, node);
-      }
-      this.token(")");
-    } else {
-      this.print(firstParam, node);
-    }
-  } else {
-    this._params(node);
-  }
+  this._params(node);
 
   this._predicate(node);
 
@@ -150,13 +120,3 @@ export function ArrowFunctionExpression(
 
   this.print(node.body, node);
 }
-
-function hasTypes(node, param) {
-  return (
-    node.typeParameters ||
-    node.returnType ||
-    param.typeAnnotation ||
-    param.optional ||
-    param.trailingComments
-  );
-}

packages/babel-generator/test/fixtures/edgecase/single-arg-async-arrow-with-retainlines/output.js

@@ -1,11 +1,11 @@
 var fn = async (
-  arg
-) => {};
+arg) =>
+{};
 
 async (x) =>
 {};
 
-async x => {};
+async (x) => {};
 
 async (x) =>
 {};

packages/babel-generator/test/fixtures/flow/arrow-functions/output.js

@@ -4,12 +4,12 @@ const bar2 = (x?) => {};
 
 const bar3 = (x?: string) => {};
 
-const bar4 = x => {};
+const bar4 = (x) => {};
 
 const bar5 = (x): string => {};
 
 const bar6 = (x: number) => {};
 
 const bar7 = <T>(x) => {};
 
-const bar8 = <T>(x: T): ((T) => T[]) => y => [x, y];
+const bar8 = <T>(x: T): ((T) => T[]) => (y) => [x, y];

packages/babel-generator/test/fixtures/flow/predicates/output.js

@@ -14,4 +14,4 @@ var f = (x: mixed): %checks => typeof x === "string";
 
 const foo2 = (x: mixed): boolean %checks => typeof x === "string";
 
-x: %checks => x !== null;
+(x): %checks => x !== null;

packages/babel-generator/test/fixtures/flow/typecasts/output.js

@@ -6,5 +6,5 @@
   xxx: number,
   yyy: string,
 });
-(xxx => xxx + 1: (xxx: number) => number);
+((xxx) => xxx + 1: (xxx: number) => number);
 (xxx: number), (yyy: string);

packages/babel-generator/test/fixtures/harmony-edgecase/arrow-function/output.js

@@ -1,15 +1,15 @@
-e => {
+(e) => {
   print("hello world");
 };
 
 (e1, e2, e3) => {
   print("hello world");
 };
 
-e => e;
+(e) => e;
 
 (e1, e2, e3) => e;
 
-e => {};
+(e) => {};
 
-e => 20 + 20;
+(e) => 20 + 20;

packages/babel-generator/test/fixtures/minified/arrow-functions/output.js

@@ -1 +1 @@
-var foo=(arg1,arg2)=>{arg1;arg2};var foo2=(arg1,arg2)=>{arg1};var foo3=arg1=>arg1;
+var foo=(arg1,arg2)=>{arg1;arg2};var foo2=(arg1,arg2)=>{arg1};var foo3=(arg1)=>arg1;

packages/babel-generator/test/fixtures/parentheses/arrow-function-object-body/output.js

@@ -1,4 +1,4 @@
-var foo = arr.map(v => ({
+var foo = arr.map((v) => ({
   x: v.bar,
   y: v.bar * 2
 }));

packages/babel-generator/test/fixtures/parentheses/arrow-function/output.js

@@ -1 +1 @@
-foo || (bar => bar());
+foo || ((bar) => bar());

packages/babel-generator/test/fixtures/parentheses/async-arrow-function/output.js

@@ -1,8 +1,8 @@
 const x = async ( // some comment
-  a) => {
+a) => {
   return foo(await a);
 };
 
 function foo(a) {
   return a;
-}
+}

packages/babel-generator/test/fixtures/types/ArrowFunctionExpression/output.js

@@ -1,7 +1,7 @@
-var foo = x => x * x;
+var foo = (x) => x * x;
 
 var foo = (a, b) => a * b;
 
-var foo = async x => x * x;
+var foo = async (x) => x * x;
 
 var foo = async (a, b) => a * b;

packages/babel-generator/test/fixtures/types/LogicalExpression/output.js

@@ -1,5 +1,5 @@
 foo || bar;
-(x => x) || bar;
+((x) => x) || bar;
 
 (function a(x) {
   return x;

packages/babel-plugin-proposal-class-properties/test/fixtures/assumption-setPublicClassFields/non-block-arrow-func/output.mjs

@@ -1,4 +1,4 @@
-export default (param => {
+export default ((param) => {
   var _class, _temp;
 
   return _temp = _class = class App {

packages/babel-plugin-proposal-class-properties/test/fixtures/private-loose/non-block-arrow-func/output.mjs

@@ -1,4 +1,4 @@
-export default (param => {
+export default ((param) => {
   var _class, _props, _temp;
 
   return _temp = (_props = babelHelpers.classPrivateFieldLooseKey("props"), _class = class App {

packages/babel-plugin-proposal-class-properties/test/fixtures/private/non-block-arrow-func/output.mjs

@@ -1,4 +1,4 @@
-export default (param => {
+export default ((param) => {
   var _class, _temp, _props;
 
   return _temp = _class = class App {

packages/babel-plugin-proposal-class-properties/test/fixtures/public-loose/non-block-arrow-func/output.mjs

@@ -1,4 +1,4 @@
-export default (param => {
+export default ((param) => {
   var _class, _temp;
 
   return _temp = _class = /*#__PURE__*/function () {

packages/babel-plugin-proposal-class-properties/test/fixtures/public/computed-without-block/output.js

@@ -1,4 +1,4 @@
-var createClass = k => {
+var createClass = (k) => {
   var _k;
 
   return _k = k(), /*#__PURE__*/function () {

packages/babel-plugin-proposal-class-properties/test/fixtures/public/non-block-arrow-func/output.mjs

@@ -1,4 +1,4 @@
-export default (param => {
+export default ((param) => {
   var _class, _temp;
 
   return _temp = _class = /*#__PURE__*/function () {

packages/babel-plugin-proposal-decorators/test/fixtures/duplicated-keys/computed-keys-same-ast/output.js

@@ -1,4 +1,4 @@
-let Foo = babelHelpers.decorate([_ => desc = _], function (_initialize) {
+let Foo = babelHelpers.decorate([(_) => desc = _], function (_initialize) {
   "use strict";
 
   class Foo {

packages/babel-plugin-proposal-decorators/test/fixtures/duplicated-keys/computed-keys-same-value/output.js

@@ -1,4 +1,4 @@
-let Foo = babelHelpers.decorate([_ => desc = _], function (_initialize) {
+let Foo = babelHelpers.decorate([(_) => desc = _], function (_initialize) {
   "use strict";
 
   class Foo {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/condition-before-break/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       if (true) {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/condition-before-expression/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       if (true) {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/declaration-before-break/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
     case 6:

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/fallthrough-block-last/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/fallthrough-block/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/fallthrough-last/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       'a';

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/fallthrough-multiblock/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/fallthrough/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       'a';

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/multi-consequent-multiblock/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/multiple-break/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       return 'a';

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/multiple-consequent-block/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/nested-break-block/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
       {

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/single-consequent-block/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
     case 6:

packages/babel-plugin-proposal-do-expressions/test/fixtures/do-expression-switch-case/single-consequent/output.js

@@ -1,4 +1,4 @@
-const x = n => function () {
+const x = (n) => function () {
   switch (n) {
     case 0:
     case 6:

packages/babel-plugin-proposal-dynamic-import/test/fixtures/amd/module/output.js

@@ -1,5 +1,5 @@
 define(["require"], function (_require) {
   "use strict";
 
-  var modP = new Promise((_resolve, _reject) => _require(["mod"], imported => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject));
+  var modP = new Promise((_resolve, _reject) => _require(["mod"], (imported) => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject));
 });

packages/babel-plugin-proposal-dynamic-import/test/fixtures/amd/no-interop/output.js

@@ -1,3 +1,3 @@
 define(["require"], function (_require) {
-  var modP = new Promise((_resolve, _reject) => _require(["mod"], imported => _resolve(imported), _reject));
+  var modP = new Promise((_resolve, _reject) => _require(["mod"], (imported) => _resolve(imported), _reject));
 });

packages/babel-plugin-proposal-dynamic-import/test/fixtures/amd/script/output.js

@@ -1,3 +1,3 @@
 define(["require"], function (_require) {
-  var modP = new Promise((_resolve, _reject) => _require(["mod"], imported => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject));
+  var modP = new Promise((_resolve, _reject) => _require(["mod"], (imported) => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject));
 });

packages/babel-plugin-proposal-dynamic-import/test/fixtures/amd/with-other-import-export/output.js

@@ -8,5 +8,5 @@ define(["require", "exports", "foo"], function (_require, _exports, _foo) {
   _foo = babelHelpers.interopRequireDefault(_foo);
   var mod;
   _exports.mod = mod;
-  new Promise((_resolve, _reject) => _require(["mod"], imported => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject)).then(m => _exports.mod = mod = m);
+  new Promise((_resolve, _reject) => _require(["mod"], (imported) => _resolve(babelHelpers.interopRequireWildcard(imported)), _reject)).then((m) => _exports.mod = mod = m);
 });

packages/babel-plugin-proposal-dynamic-import/test/fixtures/commonjs/to-string/output.js

@@ -1 +1 @@
-Promise.resolve(`${2}`).then(s => babelHelpers.interopRequireWildcard(require(s)));
+Promise.resolve(`${2}`).then((s) => babelHelpers.interopRequireWildcard(require(s)));

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-rest/parameters-object-rest-used-in-default/output.js

@@ -53,9 +53,9 @@
 };
 
 (_ref10, {
-  a = R => R
+  a = (R) => R
 } = {
-  b: R => R
+  b: (R) => R
 }) => {
   let R = babelHelpers.extends({}, _ref10);
 };

packages/babel-plugin-proposal-optional-chaining/test/fixtures/transparent-expr-wrappers/ts-as-call-context-in-if/output.js

@@ -1,4 +1,4 @@
-a => {
+(a) => {
   var _a$b;
 
   if ((_a$b = (a.b as any)) !== null && _a$b !== void 0 && _a$b.call(a)) {}

packages/babel-plugin-proposal-optional-chaining/test/fixtures/transparent-expr-wrappers/ts-as-in-conditional/output.js

@@ -1,4 +1,4 @@
-a => {
+(a) => {
   var _a$c;
 
   ((a !== null && a !== void 0 && a.b as any) && (_a$c = a.c) !== null && _a$c !== void 0 && _a$c.d as any) ? 0 : 1;

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/arrow-functions/output.js

@@ -1,13 +1,13 @@
 var _ref, _ref2, _ref3;
 
-var result = (_ref = (_ref2 = (_ref3 = [5, 10], _ref3.map(x => x * 2)), _ref2.reduce((a, b) => a + b)), _ref + 1);
+var result = (_ref = (_ref2 = (_ref3 = [5, 10], _ref3.map((x) => x * 2)), _ref2.reduce((a, b) => a + b)), _ref + 1);
 expect(result).toBe(31);
 
-var inc = x => x + 1;
+var inc = (x) => x + 1;
 
-var double = x => x * 2;
+var double = (x) => x * 2;
 
-var result2 = [4, 9].map(x => {
+var result2 = [4, 9].map((x) => {
   var _ref4, _x;
 
   return _ref4 = (_x = x, inc(_x)), double(_ref4);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/basic/output.js

@@ -1,5 +1,5 @@
 var _;
 
-var inc = x => x + 1;
+var inc = (x) => x + 1;
 
 expect((_ = 10, inc(_))).toBe(11);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/minimal/arrow-functions-parenless/output.js

@@ -1,18 +1,18 @@
 const y = 2;
 
-const f = x => {
+const f = (x) => {
   var _ref, _x;
 
   return _ref = (_x = x, _x + 1), _ref * y;
 };
 
-const g = x => {
+const g = (x) => {
   var _x2, _ref2;
 
   return _x2 = x, (_ref2 = _x2 + 1, _ref2 * _x2);
 };
 
-const h = x => {
+const h = (x) => {
   var _x3, _ref3;
 
   return _x3 = x, (_ref3 = _x3 + 1, _ref3 * _x3);