hoist var declarations to before function definition when let block scoping

lib/6to5/templates/assign.js

@@ -0,0 +1 @@
+KEY = VALUE;

lib/6to5/templates/variable-declare.js

@@ -0,0 +1 @@
+var KEY;

lib/6to5/transformers/block-binding.js

@@ -5,6 +5,7 @@ var _        = require("lodash");
 var isLet = function (node) {
   if (node.type === "VariableDeclaration" && node.kind === "let") {
     node.kind = "var";
+    node._ignoreBlockBindingHoist = true;
     return true;
   }
 };
@@ -21,7 +22,7 @@ var hasLet = function (nodes) {
 
 exports.Program = function (node) {
   if (hasLet(node.body)) {
-    node.body = [buildNode(node.body)];
+    node.body = buildNode(node.body);
   }
 };
 
@@ -31,7 +32,7 @@ exports.BlockStatement = function (node, parent) {
   // ignore if we're the body of a closure already
   if (parent.type === "FunctionExpression") return;
 
-  node.body = [buildNode(node.body)];
+  node.body = buildNode(node.body);
 };
 
 exports.ForInStatement = function (node) {
@@ -43,13 +44,47 @@ exports.ForStatement = function (node) {
 };
 
 var buildNode = function (node) {
+  var nodes = [];
+
+  // hoist normal variable declarations
+
+  node = [].concat(node);
+  node = node.map(function (node) {
+    if (node._ignoreBlockBindingHoist) return node;
+
+    if (node.type === "VariableDeclaration" && node.kind === "var") {
+      _.each(node.declarations, function (declar) {
+        nodes.push(util.template("variable-declare", {
+          KEY: declar.id
+        }));
+      });
+
+      return node.declarations.map(function (declar) {
+        return util.template("assign", {
+          KEY: declar.id,
+          VALUE: declar.init
+        }, true);
+      });
+    } else if (node.type === "ForInStatement" && !node.left._ignoreBlockBindingHoist) {
+      var id = node.left.declarations[0].id;
+      node.left = id;
+      nodes.push(util.template("variable-declare", {
+        KEY: id
+      }));
+    }
+
+    return node;
+  });
+
+  //
+
   var func = {
     type: "FunctionExpression",
     params: [],
     defaults: [],
     body: {
       type: "BlockStatement",
-      body: [].concat(node)
+      body: node
     }
   };
 
@@ -58,7 +93,11 @@ var buildNode = function (node) {
     templateName = "function-call-this";
   }
 
-  return util.template(templateName, {
+  //
+
+  nodes.push(util.template(templateName, {
     FUNCTION: func
-  }, true);
+  }, true));
+
+  return nodes;
 };

lib/6to5/traverse/index.js

@@ -30,11 +30,17 @@ var traverse = module.exports = function (parent, callback) {
       _.each(nodes, function (node, i) {
         handle(nodes, i);
       });
-      parent[key] = _.flatten(nodes).filter(function (node) {
+
+      parent[key] = _.flatten(parent[key]).filter(function (node) {
         return node !== traverse.Delete;
       });
     } else {
       handle(parent, key);
+
+      if (parent[key] === traverse.Delete) {
+        throw new Error("trying to delete property " + key + " from " +
+                        parent.type + " but can't because it's required");
+      }
     }
   });
 };
@@ -66,3 +72,18 @@ traverse.replace = function (node, callback) {
     if (result != null) obj[key] = result;
   });
 };
+
+traverse.replace.shallow = function (node, callback) {
+  traverse(node, function (node, parent, obj, key) {
+    var result = callback(node, parent);
+    if (result != null) obj[key] = result;
+    return false;
+  });
+};
+
+traverse.shallow = function (node, callback) {
+  traverse(node, function () {
+    callback.apply(this, arguments);
+    return false;
+  });
+};

test/fixtures/block-binding/hoist-multiple/actual.js

@@ -0,0 +1,2 @@
+let MULTIPLIER = 5;
+var foo = "bar", bar = "foo";

test/fixtures/block-binding/hoist-multiple/expected.js

@@ -0,0 +1,7 @@
+var foo;
+var bar;
+(function () {
+  var MULTIPLIER = 5;
+  foo = "bar";
+  bar = "foo";
+})();

test/fixtures/block-binding/hoist/actual.js

@@ -0,0 +1,2 @@
+let MULTIPLIER = 5;
+var foo = "bar";

test/fixtures/block-binding/hoist/expected.js

@@ -0,0 +1,5 @@
+var foo;
+(function () {
+  var MULTIPLIER = 5;
+  foo = "bar";
+})();

test/fixtures/constants/program/expected.js

@@ -1,6 +1,7 @@
+var i;
 (function () {
   var MULTIPLIER = 5;
-  for (var i in arr) {
+  for (i in arr) {
       console.log(arr[i] * MULTIPLIER);
   }
 }());