add basic support for assignment patterns

lib/6to5/generation/generators/expressions.js

@@ -86,6 +86,7 @@ exports.ExpressionStatement = function (node, print) {
 
 exports.BinaryExpression =
 exports.LogicalExpression =
+exports.AssignmentPattern =
 exports.AssignmentExpression = function (node, print) {
   print(node.left);
   this.push(" " + node.operator + " ");

lib/6to5/patch.js

@@ -12,6 +12,12 @@ var types = require("ast-types");
 var def   = types.Type.def;
 var or    = types.Type.or;
 
+def("AssignmentPattern")
+    .bases("Pattern")
+    .build("left", "right")
+    .field("left", def("Pattern"))
+    .field("right", def("Expression"));
+
 // Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
   .bases("Specifier")

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

@@ -20,6 +20,8 @@ var push = function (opts, nodes, elem, parentId) {
     pushObjectPattern(opts, nodes, elem, parentId);
   } else if (t.isArrayPattern(elem)) {
     pushArrayPattern(opts, nodes, elem, parentId);
+  } else if (t.isAssignmentPattern(elem)) {
+    return;
   } else {
     nodes.push(buildVariableAssign(opts, elem, parentId));
   }
@@ -48,6 +50,8 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
         var value = t.callExpression(opts.file.addHelper("object-without-properties"), [parentId, keys]);
         nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
+      if (t.isLiteral(prop.key)) prop.computed = true;
+
       var pattern2   = prop.value;
       var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
 

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

@@ -39,8 +39,9 @@
   "ForInStatement": ["Statement", "For", "Scope", "Loop"],
   "ForStatement":   ["Statement", "For", "Scope", "Loop"],
 
-  "ObjectPattern": ["Pattern"],
-  "ArrayPattern":  ["Pattern"],
+  "ObjectPattern":     ["Pattern"],
+  "ArrayPattern":      ["Pattern"],
+  "AssignmentPattern": ["Pattern"],
 
   "Property": ["UserWhitespacable"],
   "XJSElement": ["UserWhitespacable", "Expression"],

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

@@ -3,6 +3,7 @@
   "ArrayPattern":              ["elements"],
   "ArrowFunctionExpression":   ["params", "defaults", "rest", "body"],
   "AssignmentExpression":      ["left", "right"],
+  "AssignmentPattern":         ["left", "right"],
   "AwaitExpression":           ["argument"],
   "BinaryExpression":          ["left", "right"],
   "BindFunctionExpression":    ["callee", "arguments"],