split up tdz into an optional transformer until it has a better implementation - fixes #527

lib/6to5/transformation/transform.js

@@ -79,6 +79,7 @@ _.each({
 
   constants:                 require("./transformers/es6-constants"),
   letScoping:                require("./transformers/es6-let-scoping"),
+  blockScopingTDZ:           require("./transformers/optional-block-scoping-tdz"),
 
   _blockHoist:               require("./transformers/_block-hoist"),
 

lib/6to5/transformation/transformers/es6-let-scoping.js

@@ -84,7 +84,7 @@ function LetScoping(loopParent, block, parent, scope, file) {
 
   this.outsideLetReferences = {};
   this.hasLetReferences     = false;
-  this.letReferences        = {};
+  this.letReferences        = block._letReferences = {};
   this.body                 = [];
 }
 
@@ -98,7 +98,6 @@ LetScoping.prototype.run = function () {
   block._letDone = true;
 
   var needsClosure = this.getLetReferences();
-  this.checkTDZ();
 
   // this is a block within a `Function/Program` so we can safely leave it be
   if (t.isFunction(this.parent) || t.isProgram(this.block)) return;
@@ -113,48 +112,6 @@ LetScoping.prototype.run = function () {
   }
 };
 
-/**
- * Description
- */
-
-LetScoping.prototype.checkTDZ = function () {
-  var state = {
-    letRefs: this.letReferences,
-    file: this.file
-  };
-
-  traverse(this.block, {
-    enter: function (node, parent, scope, context, state) {
-      if (!t.isIdentifier(node)) return;
-      if (!t.isReferenced(node, parent)) return;
-
-      var declared = state.letRefs[node.name];
-      if (!declared) return;
-
-      // declared node is different in this scope
-      if (scope.get(node.name, true) !== declared) return;
-
-      var declaredLoc  = declared.loc;
-      var referenceLoc = node.loc;
-
-      if (!declaredLoc || !referenceLoc) return;
-
-      // does this reference appear on a line before the declaration?
-      var before = referenceLoc.start.line < declaredLoc.start.line;
-
-      if (referenceLoc.start.line === declaredLoc.start.line) {
-        // this reference appears on the same line
-        // check it appears before the declaration
-        before = referenceLoc.start.col < declaredLoc.start.col;
-      }
-
-      if (before) {
-        throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
-      }
-    }
-  }, this.scope, state);
-};
-
 /**
  * Description
  */
@@ -179,7 +136,7 @@ LetScoping.prototype.remap = function () {
       var uid = file.generateUidIdentifier(ref.name, scope).name;
       ref.name = uid;
 
-      remaps[key] = {
+      remaps[key] = remaps[uid] = {
         node: ref,
         uid: uid
       };

lib/6to5/transformation/transformers/optional-block-scoping-tdz.js

@@ -0,0 +1,47 @@
+var traverse = require("../../traverse");
+var t        = require("../../types");
+
+exports.optional = true;
+
+exports.Loop
+exports.Program =
+exports.BlockStatement = function (node, parent, scope, context, file) {
+  var letRefs = node._letReferences;
+  if (!letRefs) return;
+
+  var state = {
+    letRefs: letRefs,
+    file: file
+  };
+
+  traverse(node, {
+    enter: function (node, parent, scope, context, state) {
+      if (!t.isIdentifier(node)) return;
+      if (!t.isReferenced(node, parent)) return;
+
+      var declared = state.letRefs[node.name];
+      if (!declared) return;
+
+      // declared node is different in this scope
+      if (scope.get(node.name, true) !== declared) return;
+
+      var declaredLoc  = declared.loc;
+      var referenceLoc = node.loc;
+
+      if (!declaredLoc || !referenceLoc) return;
+
+      // does this reference appear on a line before the declaration?
+      var before = referenceLoc.start.line < declaredLoc.start.line;
+
+      if (referenceLoc.start.line === declaredLoc.start.line) {
+        // this reference appears on the same line
+        // check it appears before the declaration
+        before = referenceLoc.start.col < declaredLoc.start.col;
+      }
+
+      if (before) {
+        throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+      }
+    }
+  }, scope, state);
+};