From f7a3bdc6db7aefeeb974c0b9800bbe64d152f842 Mon Sep 17 00:00:00 2001
From: Hsiaoming Yang <me@lepture.com>
Date: Tue, 1 May 2018 14:35:55 +0900
Subject: [PATCH 1/2] Fix blueprint route for ""

---
 flask/blueprints.py      | 5 ++++-
 tests/test_blueprints.py | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/flask/blueprints.py b/flask/blueprints.py
index 3bdb3d9e32..74bca275a7 100644
--- a/flask/blueprints.py
+++ b/flask/blueprints.py
@@ -66,7 +66,10 @@ def add_url_rule(self, rule, endpoint=None, view_func=None, **options):
         blueprint's name.
         """
         if self.url_prefix is not None:
-            rule = '/'.join((self.url_prefix, rule.lstrip('/')))
+            if rule:
+                rule = '/'.join((self.url_prefix, rule.lstrip('/')))
+            else:
+                rule = self.url_prefix
         options.setdefault('subdomain', self.subdomain)
         if endpoint is None:
             endpoint = _endpoint_from_view_func(view_func)
diff --git a/tests/test_blueprints.py b/tests/test_blueprints.py
index 46364cab4d..311d77f64d 100644
--- a/tests/test_blueprints.py
+++ b/tests/test_blueprints.py
@@ -116,6 +116,7 @@ def bp_forbidden():
 
 
 @pytest.mark.parametrize(('prefix', 'rule', 'url'), (
+    ('/foo', '', '/foo'),
     ('/foo/', '/bar', '/foo/bar'),
     ('/foo/', 'bar', '/foo/bar'),
     ('/foo', '/bar', '/foo/bar'),

From b21b4d1608f5d83d7d6f503672f7eff46ed28f95 Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Tue, 1 May 2018 13:29:48 -0700
Subject: [PATCH 2/2] add more merge cases

---
 flask/blueprints.py      | 6 +++---
 tests/test_blueprints.py | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/flask/blueprints.py b/flask/blueprints.py
index 74bca275a7..5ce5561e4e 100644
--- a/flask/blueprints.py
+++ b/flask/blueprints.py
@@ -10,6 +10,7 @@
     :license: BSD, see LICENSE for more details.
 """
 from functools import update_wrapper
+from werkzeug.urls import url_join
 
 from .helpers import _PackageBoundObject, _endpoint_from_view_func
 
@@ -49,8 +50,6 @@ def __init__(self, blueprint, app, options, first_registration):
         url_prefix = self.options.get('url_prefix')
         if url_prefix is None:
             url_prefix = self.blueprint.url_prefix
-        if url_prefix:
-            url_prefix = url_prefix.rstrip('/')
         #: The prefix that should be used for all URLs defined on the
         #: blueprint.
         self.url_prefix = url_prefix
@@ -67,7 +66,8 @@ def add_url_rule(self, rule, endpoint=None, view_func=None, **options):
         """
         if self.url_prefix is not None:
             if rule:
-                rule = '/'.join((self.url_prefix, rule.lstrip('/')))
+                rule = '/'.join((
+                    self.url_prefix.rstrip('/'), rule.lstrip('/')))
             else:
                 rule = self.url_prefix
         options.setdefault('subdomain', self.subdomain)
diff --git a/tests/test_blueprints.py b/tests/test_blueprints.py
index 311d77f64d..465079cdd9 100644
--- a/tests/test_blueprints.py
+++ b/tests/test_blueprints.py
@@ -116,7 +116,12 @@ def bp_forbidden():
 
 
 @pytest.mark.parametrize(('prefix', 'rule', 'url'), (
+    ('', '/', '/'),
+    ('/', '', '/'),
+    ('/', '/', '/'),
     ('/foo', '', '/foo'),
+    ('/foo/', '', '/foo/'),
+    ('', '/bar', '/bar'),
     ('/foo/', '/bar', '/foo/bar'),
     ('/foo/', 'bar', '/foo/bar'),
     ('/foo', '/bar', '/foo/bar'),