merge es6.parameters.rest and es6.parameters.default transformers

This is necessary in order to retain correct function arity and to have
completely correct semantics. Sometimes features are tied together so much
that they would require so much desugaring to retain the correct semantics
that they'd be equivalent to... the normal transpiled output.

src/babel/transformation/transformers/deprecated.json

@@ -8,5 +8,8 @@
   "utility.inlineExpressions": "minification.constantFolding",
   "utility.deadCodeElimination": "minification.deadCodeElimination",
   "utility.removeConsoleCalls": "minification.removeConsole",
-  "utility.removeDebugger": "minification.removeDebugger"
+  "utility.removeDebugger": "minification.removeDebugger",
+
+  "es6.parameters.rest": "es6.parameters",
+  "es6.parameters.default": "es6.parameters"
 }

src/babel/transformation/transformers/es6/destructuring.js

@@ -70,7 +70,15 @@ export var visitor = {
       let pattern = node.params[i];
       if (!t.isPattern(pattern)) continue;
 
-      var ref = node.params[i] = scope.generateUidIdentifier("ref");
+      var ref = scope.generateUidIdentifier("ref");
+      if (t.isAssignmentPattern(pattern)) {
+        var _pattern = pattern;
+        pattern = pattern.left;
+        _pattern.left = ref;
+      } else {
+        node.params[i] = ref;
+      }
+
       t.inherits(ref, pattern);
 
       var destructuring = new DestructuringTransformer({

src/babel/transformation/transformers/es6/parameters/default.js

@@ -1,7 +1,7 @@
-import callDelegate from "../../helpers/call-delegate";
-import getFunctionArity from "../../helpers/get-function-arity";
-import * as util from  "../../../util";
-import * as t from "../../../types";
+import callDelegate from "../../../helpers/call-delegate";
+import getFunctionArity from "../../../helpers/get-function-arity";
+import * as util from  "../../../../util";
+import * as t from "../../../../types";
 
 var hasDefaults = function (node) {
   for (var i = 0; i < node.params.length; i++) {
@@ -38,7 +38,7 @@ export var visitor = {
 
     //
     var argsIdentifier = t.identifier("arguments");
-    argsIdentifier._shadowedFunctionLiteral = true;
+    argsIdentifier._shadowedFunctionLiteral = node;
 
     // push a default parameter definition
     function pushDefNode(left, right, i) {

src/babel/transformation/transformers/es6/parameters/index.js

@@ -0,0 +1,11 @@
+import * as util from  "../../../../util";
+import * as visitors from "../../../../traversal/visitors";
+
+import * as def from "./default";
+import * as rest from "./rest";
+
+export var metadata = {
+  group: "builtin-advanced"
+};
+
+export var visitor = visitors.merge([rest.visitor, def.visitor]);

src/babel/transformation/transformers/es6/parameters/rest.js

@@ -1,5 +1,5 @@
-import * as util from  "../../../util";
-import * as t from "../../../types";
+import * as util from  "../../../../util";
+import * as t from "../../../../types";
 
 var memberExpressionOptimisationVisitor = {
   Scope(node, parent, scope, state) {
@@ -84,7 +84,7 @@ export var visitor = {
     var argsId = t.identifier("arguments");
 
     // otherwise `arguments` will be remapped in arrow functions
-    argsId._shadowedFunctionLiteral = true;
+    argsId._shadowedFunctionLiteral = node;
 
     // support patterns
     if (t.isPattern(rest)) {

src/babel/transformation/transformers/es6/spread.js

@@ -43,6 +43,10 @@ function build(props, scope) {
   return nodes;
 }
 
+export var metadata = {
+  group: "builtin-advanced"
+};
+
 export var visitor = {
   ArrayExpression(node, parent, scope) {
     var elements = node.elements;

src/babel/transformation/transformers/es6/tail-call.js

@@ -211,7 +211,7 @@ class TailCallTransformer {
       var decl = t.variableDeclarator(this.argumentsId);
       if (this.argumentsId) {
         decl.init = t.identifier("arguments");
-        decl.init._shadowedFunctionLiteral = true;
+        decl.init._shadowedFunctionLiteral = node;
       }
       topVars.push(decl);
     }

src/babel/transformation/transformers/index.js

@@ -46,9 +46,6 @@ export default {
   "es6.regex.sticky":                      require("./es6/regex.sticky"),
   "es6.regex.unicode":                     require("./es6/regex.unicode"),
   "es6.constants":                         require("./es6/constants"),
-  "es6.parameters.rest":                   require("./es6/parameters.rest"),
-  "es6.spread":                            require("./es6/spread"),
-  "es6.parameters.default":                require("./es6/parameters.default"),
   "es7.exportExtensions":                  require("./es7/export-extensions"),
   "spec.protoToAssign":                    require("babel-plugin-proto-to-assign"),
   "es7.doExpressions":                     require("./es7/do-expressions"),
@@ -57,6 +54,8 @@ export default {
   "spec.undefinedToVoid":                  require("babel-plugin-undefined-to-void"),
 
   //- builtin-advanced
+  "es6.spread":                            require("./es6/spread"),
+  "es6.parameters":                        require("./es6/parameters"),
   "es6.destructuring":                     require("./es6/destructuring"),
   "es6.blockScoping":                      require("./es6/block-scoping"),
   "es6.spec.blockScoping":                 require("./es6/spec.block-scoping"),

src/babel/transformation/transformers/internal/shadow-functions.js

@@ -10,6 +10,9 @@ function remap(path, key, create) {
 
   var fnPath = path.findParent((path) => !path.is("shadow") && (path.isFunction() || path.isProgram()));
 
+  var shadowed = path.node._shadowedFunctionLiteral;
+  if (shadowed && shadowed !== fnPath.node) return;
+
   var cached = fnPath.getData(key);
   if (cached) return cached;
 
@@ -28,7 +31,7 @@ export var visitor = {
   },
 
   ReferencedIdentifier(node) {
-    if (node.name === "arguments" && !node._shadowedFunctionLiteral) {
+    if (node.name === "arguments") {
       return remap(this, "arguments", () => t.identifier("arguments"));
     }
   }

src/babel/traversal/visitors.js

@@ -126,6 +126,8 @@ export function merge(visitors) {
   var rootVisitor = {};
 
   for (var visitor of (visitors: Array)) {
+    explode(visitor);
+
     for (var type in visitor) {
       var nodeVisitor = rootVisitor[type] = rootVisitor[type] || {};
       mergePair(nodeVisitor, visitor[type]);