Fixed #23813 -- Added checks for common URL pattern errors

Thanks jwa and lamby for the suggestions, and timgraham and jarshwah
for their reviews.

tests/check_framework/test_urls.py

@@ -0,0 +1,37 @@
+from django.core.checks.urls import check_url_config
+from django.test import SimpleTestCase
+from django.test.utils import override_settings
+
+
+class CheckUrlsTest(SimpleTestCase):
+    @override_settings(ROOT_URLCONF='check_framework.urls_no_warnings')
+    def test_include_no_warnings(self):
+        result = check_url_config(None)
+        self.assertEqual(result, [])
+
+    @override_settings(ROOT_URLCONF='check_framework.urls_include')
+    def test_include_with_dollar(self):
+        result = check_url_config(None)
+        self.assertEqual(len(result), 1)
+        warning = result[0]
+        self.assertEqual(warning.id, 'urls.W001')
+        expected_msg = "Your URL pattern '^include-with-dollar$' uses include with a regex ending with a '$'."
+        self.assertIn(expected_msg, warning.msg)
+
+    @override_settings(ROOT_URLCONF='check_framework.urls_slash')
+    def test_url_beginning_with_slash(self):
+        result = check_url_config(None)
+        self.assertEqual(len(result), 1)
+        warning = result[0]
+        self.assertEqual(warning.id, 'urls.W002')
+        expected_msg = "Your URL pattern '/starting-with-slash/$' has a regex beginning with a '/'"
+        self.assertIn(expected_msg, warning.msg)
+
+    @override_settings(ROOT_URLCONF='check_framework.urls_name')
+    def test_url_pattern_name_with_colon(self):
+        result = check_url_config(None)
+        self.assertEqual(len(result), 1)
+        warning = result[0]
+        self.assertEqual(warning.id, 'urls.W003')
+        expected_msg = "Your URL pattern '^$' [name='name_with:colon'] has a name including a ':'."
+        self.assertIn(expected_msg, warning.msg)

tests/check_framework/urls_include.py

@@ -0,0 +1,7 @@
+from django.conf.urls import include, url
+
+urlpatterns = [
+    url(r'^', include([
+        url(r'^include-with-dollar$', include([])),
+    ])),
+]

tests/check_framework/urls_name.py

@@ -0,0 +1,13 @@
+from django.conf.urls import include, url
+from django.http import HttpResponse
+
+
+def view(request):
+    return HttpResponse('')
+
+
+urlpatterns = [
+    url('^', include([
+        url(r'^$', view, name='name_with:colon'),
+    ])),
+]

tests/check_framework/urls_no_warnings.py

@@ -0,0 +1,15 @@
+from django.conf.urls import include, url
+from django.http import HttpResponse
+
+
+def view(request):
+    return HttpResponse('')
+
+
+urlpatterns = [
+    url(r'^foo/', view, name='foo'),
+    # This dollar is ok as it is escaped
+    url(r'^\$', include([
+        url(r'^bar/$', view, name='bar'),
+    ])),
+]

tests/check_framework/urls_slash.py

@@ -0,0 +1,13 @@
+from django.conf.urls import include, url
+from django.http import HttpResponse
+
+
+def view(request):
+    return HttpResponse('')
+
+
+urlpatterns = [
+    url('^', include([
+        url(r'/starting-with-slash/$', view),
+    ])),
+]