Add block binding (let/const) support

fixes #65
+ tests

.gitignore

@@ -6,3 +6,5 @@ test/mocha.css
 
 test/tests.es5.js
 test/tests.browser.js
+
+.idea

lib/util.js

@@ -33,3 +33,22 @@ exports.guessTabWidth = function(source) {
 
   return result;
 };
+
+exports.extend = function(obj) {
+  var len = arguments.length;
+  var extension;
+
+  for (var i = 1;
+       i < len;
+       i++) {
+    if (extension = arguments[i]) {
+      for (var key in extension) {
+        if (Object.prototype.hasOwnProperty.call(extension, key)) {
+          obj[key] = extension[key];
+        }
+      }
+    }
+  }
+
+  return obj;
+}

main.js

@@ -11,22 +11,23 @@ var assert = require("assert");
 var path = require("path");
 var fs = require("fs");
 var transform = require("./lib/visit").transform;
-var guessTabWidth = require("./lib/util").guessTabWidth;
+var utils = require("./lib/util");
 var recast = require("recast");
 var esprimaHarmony = require("esprima");
 var genFunExp = /\bfunction\s*\*/;
+var blockBindingExp = /\b(let|const)\s*/;
 
 assert.ok(
   /harmony/.test(esprimaHarmony.version),
   "Bad esprima version: " + esprimaHarmony.version
 );
 
 function regenerator(source, options) {
-  if (!options) {
-    options = {
-      includeRuntime: false
-    };
-  }
+  options = utils.extend(options || {}, {
+      includeRuntime: false,
+      supportBlockBinding: true
+    }
+  );
 
   var runtime = options.includeRuntime ? fs.readFileSync(
     regenerator.runtime.dev, "utf-8"
@@ -36,15 +37,41 @@ function regenerator(source, options) {
     return runtime + source; // Shortcut: no generators to transform.
   }
 
+  var supportBlockBinding = options.supportBlockBinding;
+  if (supportBlockBinding) {
+    if (!blockBindingExp.test(source)) {
+      supportBlockBinding = false;
+    }
+  }
+
   var recastOptions = {
-    tabWidth: guessTabWidth(source),
+    tabWidth: utils.guessTabWidth(source),
     // Use the harmony branch of Esprima that installs with regenerator
     // instead of the master branch that recast provides.
-    esprima: esprimaHarmony
+    esprima: esprimaHarmony,
+    range: supportBlockBinding
   };
 
-  var ast = recast.parse(source, recastOptions);
-  var es5 = recast.print(transform(ast), recastOptions);
+  var recastAst = recast.parse(source, recastOptions);
+  var ast = recastAst.program;
+
+  if (supportBlockBinding) {// smart transpiling let/const into var
+    var defsResult = require("defs")(ast, {
+      ast: true,
+      disallowUnknownReferences: false,
+      disallowDuplicated: false,
+      disallowVars: false,
+      loopClosures: "iife"
+    });
+
+    if (defsResult.errors) {
+      throw new Error(defsResult.errors.join("\n"))
+    }
+  }
+
+  recastAst.program = transform(ast);
+
+  var es5 = recast.print(recastAst, recastOptions);
   return runtime + es5;
 }
 

package.json

@@ -31,8 +31,9 @@
     "commander": "~2.0.0",
     "esprima": "git://github.com/ariya/esprima.git#harmony",
     "ast-types": ">= 0.3.8",
-    "recast": "~0.4.23",
-    "private": "~0.0.5"
+    "recast": "~0.4.25",
+    "private": "~0.0.5",
+    "defs": "~0.6.0"
   },
   "devDependencies": {
     "mocha": "~1.13.0",

test/tests.es6.js

@@ -1048,3 +1048,61 @@ describe("new expressions", function() {
     assert.deepEqual(g.next("qwer"), { value: "qwer", done: true });
   });
 });
+
+describe("block binding", function() {
+  it("should translate block binding correctly", function() {
+    "use strict";
+
+    function *gen() {
+      var a$0 = 0, a$1 = 1;
+
+      let a = 3;
+
+      {
+        let a = 1;
+        yield a + a$0;
+      }
+
+      {
+        let a = 2;
+        yield a - 1 + a$1;
+      }
+
+      yield a;
+    }
+
+    var g = gen();
+
+    assert.deepEqual(g.next(), { value: 1, done: false });
+    assert.deepEqual(g.next(), { value: 2, done: false });
+    assert.deepEqual(g.next(), { value: 3, done: false });
+    assert.deepEqual(g.next(), { value: void 0, done: true });
+  });
+
+  it("should translate block binding with iife correctly", function() {
+    "use strict";
+
+    function *gen() {
+      let arr = [];
+
+      for (let x = 0; x < 3; x++) {
+        let y = x;
+        arr.push(function() { return y; });
+      }
+
+      {
+        let x;
+        while( x = arr.pop() ) {
+          yield x;
+        }
+      }
+    }
+
+    var g = gen();
+
+    assert.equal(g.next().value(), 2);
+    assert.equal(g.next().value(), 1);
+    assert.equal(g.next().value(), 0);
+    assert.deepEqual(g.next(), { value: void 0, done: true });
+  });
+});