Disable check_pattern_startswith_slash if settings.APPEND_SLASH=False

[Mathieu Comandon]

I would like to propose the removal of the check_pattern_startswith_slash system check as there are legitimate reasons to have url patterns starting with a slash and this warning can be misleading.

The Django framework has a strong bias in favor of trailing slashes in URLs but not everyone wishes to set up their urls that way. If this warning was to be respected, it's impossible to have urls without a trailing slash in some situations:

# myapp. urls
urlpatterns = [
    url(r'^dashboard', include('dashboard.urls')),
]

# dashboard.urls
urlpatterns = [
    url(r'^$', views.dashboard_home, name='dashboard_home'),
    url(r'^/users$', views.users, name='dashboard_users'),
]

The above URLconfs allow to have the URLs /dashboard and /dashboard/users but it will produce the warning.

When trying to make the slash optional in the root URLconf with r'^dashboard/?', the 2nd url will reverse to /dashboardusers.

I know that some system checks can be silenced but I'd be in favor of the complete removal of the check since it can be misleading for users who do not wish trailing slashes in their URLs.

[Tim Graham]

The original ticket is #23813. Maybe it's enough to disable the check if setting.APPEND_SLASH = False?

[Alasdair Nicol]

We could change the check_resolver method so that it passes the regex when called recursively.

• If we call check_resolver(resolver, r'^dashboard') then we shouldn't run check_pattern_startswith_slash. This would prevent the false positives for strycore's example.
• If we call check_resolver(resolver, r'^dashboard/') or check_resolver(resolver, None) (initial call) then it is ok to run check_pattern_startswith_slash.

I haven't tried writing a patch for this yet. Modifying the check_resolver method like this might be overly complex. I like the simplicity of checking settings.APPEND_SLASH as Tim suggested.

[Tim Graham <timograham@…>]

In 911d9f4e:

Fixed #27238 -- Disabled check_pattern_startswith_slash if settings.APPEND_SLASH=False.

Thanks strycore for the report and timgraham for suggesting the
solution.

[Tim Graham <timograham@…>]

In 190cd0e4:

[1.10.x] Fixed #27238 -- Disabled check_pattern_startswith_slash if settings.APPEND_SLASH=False.

Thanks strycore for the report and timgraham for suggesting the
solution.

Backport of 911d9f4ed1a39f945769b7198a419850378f9824 from master