RSS2 feed generates invalid category markup when 'default_feed' is 'atom'

[benward]

If you override the 'default_feed' filter to return 'atom' (to make Atom format feeds the WordPress default at /feed/), the RSS2 format is broken because it does not explicitly declare 'rss2' as its category format, instead implying the default from get_default_feed() in get_the_category_rss(). When 'default_feed' is set to 'atom', Atom formatted categories are returned in RSS.

Attached is a one line patch for feed-rss2.php, which explicitly declares the format when including categories.

(Credit for this catch to my colleague Michael Lodick at Yahoo, whose feed importer I broke with the format religiosity that exposed this bug.)

[benward]

One line patch to make 'the_category_rss' explicitly declare 'rss2' as format

[nacin]

Is this an issue for other types of data, and other feed types? Or just categories in the RSS2 feed.

[mlodick]

It looks like it's only the_category_rss() that gets called without arguments and depends on 'rss2' being the default type.

[nacin]

(In [15984]) Specify feed type in the_category_rss() call. props benward, fixes #14451.