#3391 - Add History trailingSlash option always use trailing slash …

…on root.

backbone.js

@@ -1851,6 +1851,7 @@
       // Is pushState desired ... is it available?
       this.options          = _.extend({root: '/'}, this.options, options);
       this.root             = this.options.root;
+      this._trailingSlash   = this.options.trailingSlash || false;
       this._wantsHashChange = this.options.hashChange !== false;
       this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
       this._useHashChange   = this._wantsHashChange && this._hasHashChange;
@@ -1993,10 +1994,10 @@
       // Normalize the fragment.
       fragment = this.getFragment(fragment || '');
 
-      // Don't include a trailing slash on the root.
+      // Strip trailing slash on the root unless _trailingSlash is true
       var rootPath = this.root;
-      if (fragment === '' || fragment.charAt(0) === '?') {
-        rootPath = rootPath.slice(0, -1) || '/';
+      if (!this._trailingSlash && (fragment === '' || fragment.charAt(0) === '?')) {
+        rootPath = rootPath.slice(0, -1) || '/'; // rootPath must always have at least '/'
       }
       var url = rootPath + fragment;
 

test/router.js

@@ -807,6 +807,38 @@
     Backbone.history.navigate('?x=1');
   });
 
+  QUnit.test('#3391 - Empty root normalizes to single slash.', function(assert) {
+    assert.expect(1);
+    Backbone.history.stop();
+    Backbone.history = _.extend(new Backbone.History, {
+      location: location,
+      history: {
+        pushState: function(state, title, url) {
+          assert.strictEqual(url, '/');
+        }
+      }
+    });
+    location.replace('http://example.com/root/path');
+    Backbone.history.start({pushState: true, hashChange: false, root: ''});
+    Backbone.history.navigate('');
+  });
+
+  QUnit.test('#3391 - Use trailing slash on root when trailingSlash is true.', function(assert) {
+    assert.expect(1);
+    Backbone.history.stop();
+    Backbone.history = _.extend(new Backbone.History, {
+      location: location,
+      history: {
+        pushState: function(state, title, url) {
+          assert.strictEqual(url, '/root/');
+        }
+      }
+    });
+    location.replace('http://example.com/root/path');
+    Backbone.history.start({pushState: true, hashChange: false, root: 'root', trailingSlash: true});
+    Backbone.history.navigate('');
+  });
+
   QUnit.test('#2765 - Fragment matching sans query/hash.', function(assert) {
     assert.expect(2);
     Backbone.history.stop();