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

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

4 files changed, 91 insertions, 1 deletions

diff --git a/django/core/checks/__init__.py b/django/core/checks/__init__.py
index dec2446ae2..cd21744327 100644
--- a/django/core/checks/__init__.py
+++ b/django/core/checks/__init__.py
@@ -15,6 +15,8 @@ import django.core.checks.security.base  # NOQA isort:skip
 import django.core.checks.security.csrf  # NOQA isort:skip
 import django.core.checks.security.sessions  # NOQA isort:skip
 import django.core.checks.templates  # NOQA isort:skip
+import django.core.checks.urls  # NOQA isort:skip
+
 
 __all__ = [
     'CheckMessage',
diff --git a/django/core/checks/registry.py b/django/core/checks/registry.py
index 96df429dc9..3e3d45fff8 100644
--- a/django/core/checks/registry.py
+++ b/django/core/checks/registry.py
@@ -17,6 +17,7 @@ class Tags(object):
     security = 'security'
     signals = 'signals'
     templates = 'templates'
+    urls = 'urls'
 
 
 class CheckRegistry(object):
diff --git a/django/core/checks/urls.py b/django/core/checks/urls.py
new file mode 100644
index 0000000000..a0d5b4a825
--- /dev/null
+++ b/django/core/checks/urls.py
@@ -0,0 +1,87 @@
+from __future__ import unicode_literals
+
+from . import Tags, Warning, register
+
+
+@register(Tags.urls)
+def check_url_config(app_configs, **kwargs):
+    from django.core.urlresolvers import get_resolver
+    resolver = get_resolver()
+    return check_resolver(resolver)
+
+
+def check_resolver(resolver):
+    """
+    Recursively check the resolver
+    """
+    from django.core.urlresolvers import RegexURLPattern, RegexURLResolver
+    warnings = []
+    for pattern in resolver.url_patterns:
+        if isinstance(pattern, RegexURLResolver):
+            warnings.extend(check_include_trailing_dollar(pattern))
+            # Check resolver recursively
+            warnings.extend(check_resolver(pattern))
+        elif isinstance(pattern, RegexURLPattern):
+            warnings.extend(check_pattern_name(pattern))
+
+        warnings.extend(check_pattern_startswith_slash(pattern))
+
+    return warnings
+
+
+def describe_pattern(pattern):
+    """
+    Formats the URL pattern for display in warning messages
+    """
+    description = "'{}'".format(pattern.regex.pattern)
+    if getattr(pattern, 'name', False):
+        description += " [name='{}']".format(pattern.name)
+    return description
+
+
+def check_include_trailing_dollar(pattern):
+    """
+    Checks that include is not used with a regex ending with a dollar.
+    """
+    regex_pattern = pattern.regex.pattern
+    if regex_pattern.endswith('$') and not regex_pattern.endswith('\$'):
+        warning = Warning(
+            "Your URL pattern {} uses include with a regex ending with a '$'. "
+            "Remove the dollar from the regex to avoid problems including "
+            "URLs.".format(describe_pattern(pattern)),
+            id="urls.W001",
+        )
+        return [warning]
+    else:
+        return []
+
+
+def check_pattern_startswith_slash(pattern):
+    """
+    Checks that the pattern does not begin with a forward slash
+    """
+    regex_pattern = pattern.regex.pattern
+    if regex_pattern.startswith('/') or regex_pattern.startswith('^/'):
+        warning = Warning(
+            "Your URL pattern {} has a regex beginning with a '/'. "
+            "Remove this slash as it is unnecessary.".format(describe_pattern(pattern)),
+            id="urls.W002",
+        )
+        return [warning]
+    else:
+        return []
+
+
+def check_pattern_name(pattern):
+    """
+    Checks that the pattern name does not contain a colon
+    """
+    if pattern.name is not None and ":" in pattern.name:
+        warning = Warning(
+            "Your URL pattern {} has a name including a ':'. Remove the colon, to "
+            "avoid ambiguous namespace references.".format(describe_pattern(pattern)),
+            id="urls.W003",
+        )
+        return [warning]
+    else:
+        return []
diff --git a/django/core/urlresolvers.py b/django/core/urlresolvers.py
index e462c343dc..3554878865 100644
--- a/django/core/urlresolvers.py
+++ b/django/core/urlresolvers.py
@@ -146,7 +146,7 @@ def get_callable(lookup_view, can_fail=False):
 
 
 @lru_cache.lru_cache(maxsize=None)
-def get_resolver(urlconf):
+def get_resolver(urlconf=None):
     if urlconf is None:
         from django.conf import settings
         urlconf = settings.ROOT_URLCONF