track arrays to avoid turning something into an array multiple times - closes #757

lib/6to5/transformation/file.js

@@ -226,24 +226,6 @@ File.prototype.debug = function (msg) {
   util.debug(parts);
 };
 
-File.prototype.toArray = function (node, i, forceHelperName) {
-  if (t.isArrayExpression(node)) {
-    return node;
-  } else if (t.isIdentifier(node) && node.name === "arguments") {
-    return t.callExpression(t.memberExpression(this.addHelper("slice"), t.identifier("call")), [node]);
-  } else {
-    var helperName = "to-array";
-    var args = [node];
-    if (i === true) {
-      helperName = "to-consumable-array";
-    } else if (i) {
-      args.push(t.literal(i));
-      helperName = "sliced-to-array";
-    }
-    return t.callExpression(this.addHelper(helperName), args);
-  }
-};
-
 File.prototype.getModuleFormatter = function (type) {
   var ModuleFormatter = isFunction(type) ? type : transform.moduleFormatters[type];
 

lib/6to5/transformation/transformers/es6/destructuring.js

@@ -144,12 +144,14 @@ DestructuringTransformer.prototype.pushArrayPattern = function (pattern, parentI
   // if we have a rest then we need all the elements
   var count = !hasRest(pattern) && pattern.elements.length;
 
-  var toArray = this.file.toArray(parentId, count);
+  var toArray = this.scope.toArray(parentId, count);
 
-  var _parentId = this.scope.generateUidBasedOnNode(parentId, this.file);
+  var _parentId = this.scope.generateUidBasedOnNode(parentId);
   this.nodes.push(this.buildVariableDeclaration(_parentId, toArray));
   parentId = _parentId;
 
+  this.scope.assignTypeGeneric(parentId.name, "Array");
+
   for (var i = 0; i < pattern.elements.length; i++) {
     var elem = pattern.elements[i];
 
@@ -159,7 +161,7 @@ DestructuringTransformer.prototype.pushArrayPattern = function (pattern, parentI
     var newPatternId;
 
     if (t.isRestElement(elem)) {
-      newPatternId = this.file.toArray(parentId);
+      newPatternId = this.scope.toArray(parentId);
 
       if (i > 0) {
         newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);

lib/6to5/transformation/transformers/es6/parameters.rest.js

@@ -60,6 +60,8 @@ exports.Function = function (node, parent, scope) {
     node.body.body.unshift(restDeclar);
   }
 
+  scope.assignTypeGeneric(rest.name, "Array");
+
   var loop = util.template("rest", {
     ARGUMENTS: argsId,
     ARRAY_KEY: arrKey,

lib/6to5/transformation/transformers/es6/spread.js

@@ -5,8 +5,8 @@ var t        = require("../../../types");
 
 exports.check = t.isSpreadElement;
 
-var getSpreadLiteral = function (spread, file) {
-  return file.toArray(spread.argument, true);
+var getSpreadLiteral = function (spread, scope) {
+  return scope.toArray(spread.argument, true);
 };
 
 var hasSpread = function (nodes) {
@@ -18,7 +18,7 @@ var hasSpread = function (nodes) {
   return false;
 };
 
-var build = function (props, file) {
+var build = function (props, scope) {
   var nodes = [];
 
   var _props = [];
@@ -33,7 +33,7 @@ var build = function (props, file) {
     var prop = props[i];
     if (t.isSpreadElement(prop)) {
       push();
-      nodes.push(getSpreadLiteral(prop, file));
+      nodes.push(getSpreadLiteral(prop, scope));
     } else {
       _props.push(prop);
     }
@@ -44,11 +44,11 @@ var build = function (props, file) {
   return nodes;
 };
 
-exports.ArrayExpression = function (node, parent, scope, file) {
+exports.ArrayExpression = function (node, parent, scope) {
   var elements = node.elements;
   if (!hasSpread(elements)) return;
 
-  var nodes = build(elements, file);
+  var nodes = build(elements, scope);
   var first = nodes.shift();
 
   if (!t.isArrayExpression(first)) {
@@ -59,7 +59,7 @@ exports.ArrayExpression = function (node, parent, scope, file) {
   return t.callExpression(t.memberExpression(first, t.identifier("concat")), nodes);
 };
 
-exports.CallExpression = function (node, parent, scope, file) {
+exports.CallExpression = function (node, parent, scope) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
@@ -71,7 +71,7 @@ exports.CallExpression = function (node, parent, scope, file) {
   if (args.length === 1 && args[0].argument.name === "arguments") {
     nodes = [args[0].argument];
   } else {
-    nodes = build(args, file);
+    nodes = build(args, scope);
   }
 
   var first = nodes.shift();
@@ -105,7 +105,7 @@ exports.NewExpression = function (node, parent, scope, file) {
 
   var nativeType = t.isIdentifier(node.callee) && includes(t.NATIVE_TYPE_NAMES, node.callee.name);
 
-  var nodes = build(args, file);
+  var nodes = build(args, scope);
 
   if (nativeType) {
     nodes.unshift(t.arrayExpression([t.literal(null)]));

lib/6to5/transformation/transformers/index.js

@@ -31,7 +31,6 @@ module.exports = {
   "es6.objectSuper":                       require("./es6/object-super"),
   "es7.objectRestSpread":                  require("./es7/object-rest-spread"),
   "es7.exponentiationOperator":            require("./es7/exponentiation-operator"),
-  "es6.spread":                            require("./es6/spread"),
   "es6.templateLiterals":                  require("./es6/template-literals"),
 
   "es5.properties.mutators":               require("./es5/properties.mutators"),
@@ -50,6 +49,9 @@ module.exports = {
   // needs to be before `es6.parameters.default` as default parameters will destroy the rest param
   "es6.parameters.rest":                   require("./es6/parameters.rest"),
 
+  // needs to be after `es6.parameters.rest` as we use `toArray` and avoid turning an already known array into one
+  "es6.spread":                            require("./es6/spread"),
+
   // needs to be before `es6.blockScoping` as default parameters have a TDZ
   "es6.parameters.default":                require("./es6/parameters.default"),
 

lib/6to5/traversal/scope.js

@@ -198,6 +198,25 @@ Scope.prototype.inferType = function (node) {
   }
 };
 
+Scope.prototype.isTypeGeneric = function (name, genericName) {
+  var info = this.getBindingInfo(name);
+  if (!info) return false;
+
+  var type = info.typeAnnotation;
+  return t.isGenericTypeAnnotation(type) && t.isIdentifier(type.id, { name: genericName });
+};
+
+Scope.prototype.assignTypeGeneric = function (name, type) {
+  this.assignType(name, t.genericTypeAnnotation(t.identifier(type)));
+};
+
+Scope.prototype.assignType = function (name, type) {
+  var info = this.getBindingInfo(name);
+  if (!info) return;
+
+  info.identifier.typeAnnotation = info.typeAnnotation = type;
+};
+
 Scope.prototype.getTypeAnnotation = function (key, id, node) {
   var type;
 
@@ -215,6 +234,32 @@ Scope.prototype.getTypeAnnotation = function (key, id, node) {
   }
 };
 
+Scope.prototype.toArray = function (node, i) {
+  var file = this.file;
+
+  if (t.isIdentifier(node) && this.isTypeGeneric(node.name, "Array")) {
+    return node;
+  }
+
+  if (t.isArrayExpression(node)) {
+    return node;
+  }
+
+  if (t.isIdentifier(node, { name: "arguments" })) {
+    return t.callExpression(t.memberExpression(file.addHelper("slice"), t.identifier("call")), [node]);
+  }
+
+  var helperName = "to-array";
+  var args = [node];
+  if (i === true) {
+    helperName = "to-consumable-array";
+  } else if (i) {
+    args.push(t.literal(i));
+    helperName = "sliced-to-array";
+  }
+  return t.callExpression(file.addHelper(helperName), args);
+};
+
 Scope.prototype.clearOwnBinding = function (name) {
   delete this.bindings[name];
 };

lib/6to5/types/builder-keys.json

@@ -59,6 +59,11 @@
     "generator": false
   },
 
+  "GenericTypeAnnotation": {
+    "id": null,
+    "typeParameters": null
+  },
+
   "Identifier": {
     "name": null
   },