From c7d69b2f92cf9aa26cafc2ace3cdf29acaee0bba Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Wed, 10 Dec 2014 23:49:13 +1100
Subject: [PATCH] block scope constants

---
 .../transformers/es6-constants.js             | 20 ++++++++++++++++---
 lib/6to5/traverse/scope.js                    | 17 +++++++++-------
 .../es6-constants/block-scoped/exec.js        |  3 +++
 3 files changed, 30 insertions(+), 10 deletions(-)
 create mode 100644 test/fixtures/transformation/es6-constants/block-scoped/exec.js

diff --git a/lib/6to5/transformation/transformers/es6-constants.js b/lib/6to5/transformation/transformers/es6-constants.js
index 15f2c8c45b..2996974c37 100644
--- a/lib/6to5/transformation/transformers/es6-constants.js
+++ b/lib/6to5/transformation/transformers/es6-constants.js
@@ -9,11 +9,21 @@ exports.ForOfStatement =
 exports.ForStatement = function (node, parent, file) {
   var constants = {};
 
-  var check = function (parent, names) {
+  /**
+   * Check the results of `util.getIds` as `names` generated from a
+   * node against it's parent.
+   */
+
+  var check = function (parent, names, scope) {
     _.each(names, function (nameNode, name) {
       if (!_.has(constants, name)) return;
       if (parent && t.isBlockStatement(parent) && parent !== constants[name]) return;
 
+      if (scope) {
+        var defined = scope.get(name);
+        if (defined && defined === nameNode) return;
+      }
+
       throw file.errorWithNode(nameNode, name + " is read-only");
     });
   };
@@ -22,6 +32,10 @@ exports.ForStatement = function (node, parent, file) {
     return t.getIds(node, true, ["MemberExpression"]);
   };
 
+  /**
+   * Collect all constants in this scope.
+   */
+
   _.each(node.body, function (child, parent) {
     if (child && t.isVariableDeclaration(child, { kind: "const" })) {
       _.each(child.declarations, function (declar) {
@@ -43,12 +57,12 @@ exports.ForStatement = function (node, parent, file) {
 
   if (_.isEmpty(constants)) return;
 
-  traverse(node, function (child, parent) {
+  traverse(node, function (child, parent, scope) {
     if (child._ignoreConstant) return;
     if (t.isVariableDeclaration(child)) return;
 
     if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-      check(parent, getIds(child));
+      check(parent, getIds(child), scope);
     }
   });
 };
diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index 50bb67243c..b2faeab838 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -27,12 +27,12 @@ Scope.add = function (node, references) {
 };
 
 Scope.prototype.generateTemp = function (file, name) {
-    var id = file.generateUidIdentifier(name || "temp", this);
-    this.push({
-      key: id.name,
-      id: id
-    });
-    return id;
+  var id = file.generateUidIdentifier(name || "temp", this);
+  this.push({
+    key: id.name,
+    id: id
+  });
+  return id;
 };
 
 Scope.prototype.getReferences = function () {
@@ -86,12 +86,15 @@ Scope.prototype.getReferences = function () {
       // declared within are accessible
       if (t.isFunction(node)) return false;
 
+      // function identifier doesn't belong to this scope
+      if (block.id && node === block.id) return;
+
       if (t.isIdentifier(node) && t.isReferenced(node, parent) && !scope.has(node.name)) {
         add(node);
       }
 
       // we've ran into a declaration!
-      // we'll let the BlockStatement scope deal with `let` declarations
+      // we'll let the BlockStatement scope deal with `let` declarations unless
       if (t.isDeclaration(node) && !t.isLet(node)) {
         add(node);
       }
diff --git a/test/fixtures/transformation/es6-constants/block-scoped/exec.js b/test/fixtures/transformation/es6-constants/block-scoped/exec.js
new file mode 100644
index 0000000000..c46d684d19
--- /dev/null
+++ b/test/fixtures/transformation/es6-constants/block-scoped/exec.js
@@ -0,0 +1,3 @@
+const bar = 123;
+{ const bar = 456; }
+assert.equal(bar, 123);