Make sure middleware layer sorting is stable

See https://github.com/strongloop/strong-arc/issues/767

lib/server-app.js

@@ -214,13 +214,22 @@ proto._sortLayersByPhase = function() {
   });
 
   var router = this._router;
+
+  // See https://code.google.com/p/v8/issues/detail?id=90
+  router.stack.forEach(function(layer, ix) {
+    layer.order = ix;
+  });
   router.stack.sort(compareLayers);
 
   function compareLayers(left, right) {
     var leftPhase = left.phase;
     var rightPhase = right.phase;
 
-    if (leftPhase === rightPhase) return 0;
+    var result;
+    if (leftPhase === rightPhase) {
+      // Keep the order (stable sorting)
+      return left.order - right.order;
+    }
 
     // Builtin middleware is always first
     if (leftPhase === BUILTIN_MIDDLEWARE) return -1;
@@ -232,13 +241,23 @@ proto._sortLayersByPhase = function() {
       if (rightPhase === 'routes')
         return -1;
 
-      return phaseOrder['routes'] - phaseOrder[rightPhase];
+      result = phaseOrder['routes'] - phaseOrder[rightPhase];
+      if (result === 0) {
+        return left.order - right.order;
+      } else {
+        return result;
+      }
     }
 
     if (rightPhase === undefined)
       return -compareLayers(right, left);
 
     // Layers registered via `app.middleware` are compared via phase & hook
-    return phaseOrder[leftPhase] - phaseOrder[rightPhase];
+    result = phaseOrder[leftPhase] - phaseOrder[rightPhase];
+    if (result === 0) {
+      return left.order - right.order;
+    } else {
+      return result;
+    }
   }
 };

test/app.test.js

@@ -297,6 +297,19 @@ describe('app', function() {
       });
     });
 
+    it('keep orders of middleware added by app.use()', function(done) {
+      var expectedSteps = [];
+      for (var i = 0; i < 10; i++) {
+        app.use(namedHandler('m' + i));
+        expectedSteps.push('m' + i);
+      }
+      executeMiddlewareHandlers(app, function(err) {
+        if (err) return done(err);
+        expect(steps).to.eql(expectedSteps);
+        done();
+      });
+    });
+
     function namedHandler(name) {
       return function(req, res, next) {
         steps.push(name);