Fixed #1314: yielding a function should not call the function (#1315)

* Fixed #1314:  yielding a function should not call the function
   When rejecting a non-promise value, string.replace is used,
    and the value is passed as second parameter.
    But string.replace, if the second value is a function, will
    call that function.
    This commit fixes this by using value.toString().

* changed how value is converted to string in error about yielding non-promises

src/generators.js

@@ -160,7 +160,7 @@ PromiseSpawn.prototype._continue = function (result) {
             if (maybePromise === null) {
                 this._promiseRejected(
                     new TypeError(
-                        YIELDED_NON_PROMISE_ERROR.replace("%s", value) +
+                        YIELDED_NON_PROMISE_ERROR.replace("%s", String(value)) +
                         FROM_COROUTINE_CREATED_AT +
                         this._stack.split("\n").slice(1, -7).join("\n")
                     )

test/mocha/generator.js

@@ -82,6 +82,22 @@ describe("yielding", function() {
             assert.equal(val, 4);
         });
     });
+
+    specify("yielding a function should not call the function", function() {
+        let functionWasCalled = false;
+        return Promise.coroutine(function*(){
+            try {
+                yield (function() {functionWasCalled = true;});
+            } 
+            catch(e){
+                assert(e instanceof TypeError);
+                assert.equal(functionWasCalled, false);
+                return 4;
+            }
+        })().then(function(val){
+            assert.equal(val, 4);
+        });
+    });
 });
 
 describe("thenables", function(){
@@ -367,7 +383,7 @@ describe("Spawn", function() {
 describe("custom yield handlers", function() {
     specify("should work with timers", function() {
         var n = 0;
-        return Promise.coroutine.addYieldHandler(function(v) {
+        Promise.coroutine.addYieldHandler(function(v) {
             if (typeof v === "number") {
                 n = 1;
                 return Promise.resolve(n);
@@ -417,18 +433,18 @@ describe("custom yield handlers", function() {
         });
     });
 
-    Promise.coroutine.addYieldHandler(function(v) {
-        if (typeof v === "function") {
-            var cb;
-            var promise = Promise.fromNode(function(callback) {
-                cb = callback;
-            });
-            try { v(cb); } catch (e) { cb(e); }
-            return promise;
-        }
-    });
-
     specify("should work with thunks", function(){
+        Promise.coroutine.addYieldHandler(function(v) {
+            if (typeof v === "function") {
+                var cb;
+                var promise = Promise.fromNode(function(callback) {
+                    cb = callback;
+                });
+                try { v(cb); } catch (e) { cb(e); }
+                return promise;
+            }
+        });
+
         var thunk = function(a) {
             return function(callback) {
                 setTimeout(function(){