add optional asyncToGenerator transformer - closes #321

lib/6to5/file.js

@@ -27,7 +27,12 @@ File.declarations = [
   "object-without-properties",
   "has-own",
   "slice",
-  "define-property"
+  "define-property",
+  "async-to-generator"
+];
+
+File.excludeDeclarationsFromRuntime = [
+  "async-to-generator"
 ];
 
 File.normaliseOptions = function (opts) {
@@ -166,7 +171,7 @@ File.prototype.addDeclaration = function (name) {
 
   var ref;
   var runtimeNamespace = this.opts.runtime;
-  if (runtimeNamespace) {
+  if (runtimeNamespace && !_.contains(File.excludeDeclarationsFromRuntime, name)) {
     name = t.identifier(t.toIdentifier(name));
     return t.memberExpression(t.identifier(runtimeNamespace), name);
   } else {

lib/6to5/runtime-generator.js

@@ -19,6 +19,10 @@ module.exports = function (namespace) {
   ]));
 
   _.each(File.declarations, function (name) {
+    if (_.contains(File.excludeDeclarationsFromRuntime, name)) {
+      return false;
+    }
+
     var key = t.identifier(t.toIdentifier(name));
     body.push(t.expressionStatement(
       t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))

lib/6to5/transformation/templates/async-to-generator.js

@@ -0,0 +1,37 @@
+(function (fn) {
+  return function () {
+    var gen = fn.apply(this, arguments);
+
+    return new Promise(function (resolve, reject) {
+      function step(getNext) {
+        var next;
+
+        try {
+          next = getNext();
+        } catch(e) {
+          reject(e);
+          return;
+        }
+
+        if (next.done) {
+          resolve(next.value);
+          return;
+        }
+
+        Promise.resolve(next.value).then(function (v) {
+          step(function () {
+            return gen.next(v);
+          });
+        }, function (e) {
+          step(function () {
+            return gen["throw"](e);
+          });
+        });
+      }
+
+      step(function () {
+        return gen.next();
+      });
+    });
+  }
+})

lib/6to5/transformation/transform.js

@@ -49,6 +49,7 @@ _.each({
   memoizationOperator:       require("./transformers/playground-memoization-operator"),
   objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),
 
+  asyncToGenerator:          require("./transformers/optional-async-to-generator"),
   bluebirdCoroutines:        require("./transformers/optional-bluebird-coroutines"),
 
   react:                     require("./transformers/react"),

lib/6to5/transformation/transformers/optional-async-to-generator.js

@@ -0,0 +1,15 @@
+var bluebirdCoroutines = require("./optional-bluebird-coroutines");
+var traverse           = require("../../traverse");
+var t                  = require("../../types");
+
+exports.optional = true;
+
+exports.manipulateOptions = bluebirdCoroutines.manipulateOptions;
+
+exports.Function = function (node, parent, file) {
+  if (!node.async || node.generator) return;
+
+  bluebirdCoroutines._Function(node);
+
+  return t.callExpression(file.addDeclaration("async-to-generator"), [node]);
+};

lib/6to5/transformation/transformers/optional-bluebird-coroutines.js

@@ -8,9 +8,7 @@ exports.manipulateOptions = function (opts) {
 
 exports.optional = true;
 
-exports.Function = function (node, parent, file) {
-  if (!node.async || node.generator) return;
-
+exports._Function = function (node) {
   node.async = false;
   node.generator = true;
 
@@ -23,6 +21,12 @@ exports.Function = function (node, parent, file) {
       }
     }
   });
+};
+
+exports.Function = function (node, parent, file) {
+  if (!node.async || node.generator) return;
+
+  exports._Function(node);
 
   var id = t.identifier("Bluebird");
   file.addImport(id, "bluebird");