[ES7] Trailing comma in function parameter list

Currenly a stage 1 proposal.
See https://github.com/jeffmo/es-trailing-function-commas.

src/acorn/src/expression.js

@@ -224,7 +224,7 @@ pp.parseSubscripts = function(base, start, noCalls) {
   } else if (!noCalls && this.eat(tt.parenL)) {
     let node = this.startNodeAt(start)
     node.callee = base
-    node.arguments = this.parseExprList(tt.parenR, false)
+    node.arguments = this.parseExprList(tt.parenR, this.options.features["es7.trailingFunctionCommas"])
     return this.parseSubscripts(this.finishNode(node, "CallExpression"), start, noCalls)
   } else if (this.type === tt.backQuote) {
     let node = this.startNodeAt(start)

src/acorn/src/statement.js

@@ -458,7 +458,7 @@ pp.parseFunction = function(node, isStatement, allowExpressionBody, isAsync) {
 
 pp.parseFunctionParams = function(node) {
   this.expect(tt.parenL)
-  node.params = this.parseBindingList(tt.parenR, false, false)
+  node.params = this.parseBindingList(tt.parenR, false, this.options.features["es7.trailingFunctionCommas"])
 }
 
 // Parse a class declaration or literal (depending on the

src/babel/transformation/transformers/es7/trailing-function-commas.js

@@ -0,0 +1,7 @@
+export var metadata = {
+  stage: 1
+};
+
+export function check() {
+  return false;
+}

src/babel/transformation/transformers/index.js

@@ -1,5 +1,6 @@
 export default {
   "es7.classProperties":                   require("./es7/class-properties"),
+  "es7.trailingFunctionCommas":            require("./es7/trailing-function-commas"),
   "es7.asyncFunctions":                    require("./es7/async-functions"),
   "es7.decorators":                        require("./es7/decorators"),
 

test/core/fixtures/transformation/es7.trailing-function-commas/call/actual.js

@@ -0,0 +1,4 @@
+Math.max(1,
+         2,
+         3,
+);

test/core/fixtures/transformation/es7.trailing-function-commas/call/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+Math.max(1, 2, 3);

test/core/fixtures/transformation/es7.trailing-function-commas/declaration/actual.js

@@ -0,0 +1,8 @@
+function thisIsAFunctionWithAVeryLongNameAndWayTooManyParameters(
+  thisIsTheFirstParameter, andThisOneIsRelatedToIt,
+  butNotThisOne,
+  andNeitherThis,
+  inFactThereArentThatManyParameters,
+) {
+  throw null;
+}

test/core/fixtures/transformation/es7.trailing-function-commas/declaration/expected.js

@@ -0,0 +1,5 @@
+"use strict";
+
+function thisIsAFunctionWithAVeryLongNameAndWayTooManyParameters(thisIsTheFirstParameter, andThisOneIsRelatedToIt, butNotThisOne, andNeitherThis, inFactThereArentThatManyParameters) {
+  throw null;
+}

test/core/fixtures/transformation/es7.trailing-function-commas/options.json

@@ -0,0 +1,3 @@
+{
+  "optional": ["es7.trailingFunctionCommas"]
+}