Add retainFunctionParens option (#4621)

* Add retainParens option

* Add doc, remove option

* Add negation test

* Make sure parens are not added

* Change name

* Change dir name

packages/babel-generator/README.md

@@ -30,6 +30,7 @@ auxiliaryCommentBefore | string   |                 | Optional string to add as
 auxiliaryCommentAfter  | string   |                 | Optional string to add as a block comment at the end of the output file
 shouldPrintComment     | function | `opts.comments` | Function that takes a comment (as a string) and returns `true` if the comment should be included in the output.  By default, comments are included if `opts.comments` is `true` or if `opts.minifed` is `false` and the comment contains `@preserve` or `@license`
 retainLines            | boolean  | `false`         | Attempt to use the same line numbers in the output code as in the source code (helps preserve stack traces)
+retainFunctionParens   | boolean  | `false`         | Retain parens around function expressions (could be used to change engine parsing behavior)
 comments               | boolean  | `true`          | Should comments be included in output
 compact                | boolean or `'auto'` | `opts.minified` | Set to `true` to avoid adding whitespace for formatting
 minified               | boolean  | `false`         | Should the output be minified

packages/babel-generator/src/index.js

@@ -53,6 +53,7 @@ function normalizeOptions(code, opts, tokens): Format {
     auxiliaryCommentAfter: opts.auxiliaryCommentAfter,
     shouldPrintComment: opts.shouldPrintComment,
     retainLines: opts.retainLines,
+    retainFunctionParens: opts.retainFunctionParens,
     comments: opts.comments == null || opts.comments,
     compact: opts.compact,
     minified: opts.minified,

packages/babel-generator/src/printer.js

@@ -16,6 +16,7 @@ const NON_DECIMAL_LITERAL = /^0[box]/;
 export type Format = {
   shouldPrintComment: (comment: string) => boolean;
   retainLines: boolean;
+  retainFunctionParens: boolean;
   comments: boolean;
   auxiliaryCommentBefore: string;
   auxiliaryCommentAfter: string;
@@ -330,6 +331,11 @@ export default class Printer {
     this._maybeAddAuxComment(this._insideAux && !oldInAux);
 
     let needsParens = n.needsParens(node, parent, this._printStack);
+    if (this.format.retainFunctionParens &&
+        node.type === "FunctionExpression" &&
+        node.extra && node.extra.parenthesized) {
+      needsParens = true;
+    }
     if (needsParens) this.token("(");
 
     this._printLeadingComments(node, parent);

packages/babel-generator/test/fixtures/retainFunctionParens/argument/actual.js

@@ -0,0 +1 @@
+__d('x', (function () {}));

packages/babel-generator/test/fixtures/retainFunctionParens/argument/expected.js

@@ -0,0 +1 @@
+__d('x', (function () {}));

packages/babel-generator/test/fixtures/retainFunctionParens/assignment/actual.js

@@ -0,0 +1 @@
+var x = (function () {});

packages/babel-generator/test/fixtures/retainFunctionParens/assignment/expected.js

@@ -0,0 +1 @@
+var x = (function () {});

packages/babel-generator/test/fixtures/retainFunctionParens/negation/actual.js

@@ -0,0 +1 @@
+!function (){}()

packages/babel-generator/test/fixtures/retainFunctionParens/negation/expected.js

@@ -0,0 +1 @@
+!function () {}();

packages/babel-generator/test/fixtures/retainFunctionParens/nested/actual.js

@@ -0,0 +1 @@
+var x = (((function () { })));

packages/babel-generator/test/fixtures/retainFunctionParens/nested/expected.js

@@ -0,0 +1 @@
+var x = (function () {});

packages/babel-generator/test/fixtures/retainFunctionParens/no-parens/actual.js

@@ -0,0 +1 @@
+callback(function () {});

packages/babel-generator/test/fixtures/retainFunctionParens/no-parens/expected.js

@@ -0,0 +1 @@
+callback(function () {});

packages/babel-generator/test/fixtures/retainFunctionParens/options.json

@@ -0,0 +1,3 @@
+{
+  "retainFunctionParens": true
+}