add AssignmentPattern support to scope tracking - fixes #537

lib/6to5/types/index.js

@@ -487,7 +487,8 @@ t.getIds.nodes = {
   MemeberExpression: ["object"],
   SpreadElement: ["argument"],
   Property: ["value"],
-  ComprehensionBlock: ["left"]
+  ComprehensionBlock: ["left"],
+  AssignmentPattern: ["left"]
 };
 
 t.getIds.arrays = {

test/fixtures/transformation/es6-let-scoping/exec-destructuring-defaults/exec.js

@@ -0,0 +1,5 @@
+var fields = [{ name: "title" }, { name: "content" }];
+
+for (let { name, value = "Default value" } of fields) {
+  assert.equal(value, "Default value");
+}