From 9d6165d03be1d03ae530a151451be0cb8f1762d7 Mon Sep 17 00:00:00 2001
From: Kyle Dickerson <dickerson9@llnl.gov>
Date: Thu, 12 Mar 2020 14:08:34 -0700
Subject: [PATCH] #3391 - Add History `trailingSlash` option always use
 trailing slash on root.

---
 backbone.js    |  7 ++++---
 test/router.js | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/backbone.js b/backbone.js
index bc4f18f9a..35730a687 100644
--- a/backbone.js
+++ b/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;
 
diff --git a/test/router.js b/test/router.js
index c33901883..c60eb7418 100644
--- a/test/router.js
+++ b/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();