#36775: Raise ImproperlyConfigured when Feed.link is missing instead of failing
with AttributeError
-------------------------------------+-------------------------------------
     Reporter:  yureiblack           |                    Owner:
         Type:                       |  yureiblack
  Cleanup/optimization               |                   Status:  assigned
    Component:  contrib.syndication  |                  Version:  dev
     Severity:  Normal               |               Resolution:
     Keywords:                       |             Triage Stage:  Accepted
    Has patch:  1                    |      Needs documentation:  0
  Needs tests:  1                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------
Changes (by Jacob Walls):

 * needs_tests:  0 => 1
 * owner:  (none) => yureiblack
 * stage:  Unreviewed => Accepted
 * status:  new => assigned
 * type:  Bug => Cleanup/optimization


Old description:

> Currently, the `Feed.get_feed()` method retrieves the feed's `link`
> using:
>
>     link = self._get_dynamic_attr("link", obj)
>
> If a Feed subclass does not define a `link` attribute, `link` becomes
> `None`.
> This results in an unhelpful exception when Django later calls:
>
>     link = add_domain(current_site.domain, link, request.is_secure())
>
> Since `add_domain()` calls `url.startswith()`, a missing `link`
> causes:
>
>     AttributeError: 'NoneType' object has no attribute 'startswith'
>
> This error does not clearly indicate the actual problem.
>
> According to Django documentation, every `Feed` class must define
> `link`. Therefore, it should raise a more appropriate and explicit
> exception.
>
> The attached PR adds the following check:
>
>     if link is None:
>         raise ImproperlyConfigured(
>             "Feed class must define a 'link' attribute."
>         )
>
> This results in a clearer error message and avoids unexpected crashes.
>
> PR: https://github.com/django/django/pull/20371

New description:

 Currently, the `Feed.get_feed()` method retrieves the feed's `link` using:
 {{{#!py
     link = self._get_dynamic_attr("link", obj)
 }}}
 If a Feed subclass does not define a `link` attribute, `link` becomes
 `None`.
 This results in an unhelpful exception when Django later calls:
 {{{#!py
     link = add_domain(current_site.domain, link, request.is_secure())
 }}}
 Since `add_domain()` calls `url.startswith()`, a missing `link`
 causes:
 {{{#!py
     AttributeError: 'NoneType' object has no attribute 'startswith'
 }}}
 This error does not clearly indicate the actual problem.

 According to Django documentation, every `Feed` class must define
 `link`. Therefore, it should raise a more appropriate and explicit
 exception.

 The attached PR adds the following check:
 {{{#!py
     if link is None:
         raise ImproperlyConfigured(
             "Feed class must define a 'link' attribute."
         )
 }}}
 This results in a clearer error message and avoids unexpected crashes.

 PR: https://github.com/django/django/pull/20371

--
Comment:

 Seems reasonable, thanks. (I think this is the "better error" described as
 "wouldn't kill us" in a very similar scenario in ticket:2218#comment:1.)

 Could you include a test?
-- 
Ticket URL: <https://code.djangoproject.com/ticket/36775#comment:1>
Django <https://code.djangoproject.com/>
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