bbp_rel_nofollow() can create multiple rel attributes

[SergeyBiryukov]

In [4866], wp_rel_nofollow() was replaced with bbp_rel_nofollow().

It's not quite clear to me from the commit message what was wrong with wp_rel_nofollow(), as bbp_rel_nofollow() is almost identical to ​what was in WordPress trunk at the time, except for stripslashes()/wp_slash().

The issue is that bbp_rel_nofollow() in its current form does not account for two cases:

• <a href="foo" rel="bar nofollow"> is turned into <a href="foo" rel="bar nofollow" rel="nofollow">, and multiple rel attributes is invalid markup. This was fixed for WordPress in ​[WP34277], see ​#WP9959.
• Links with the site's own domain should not be nofollowed. This was fixed for WordPress in ​[WP36125], see ​#WP11360.

Any chance for bbPress to use wp_rel_nofollow() again? If not, I'll submit a patch that backports ​[WP34277] and ​[WP36125] to bbp_rel_nofollow(), with some unit tests.

[johnjamesjacoby]

The bbPress specific version was used for links inside of code blocks dating back to 2013, and WordPress caught up in 2015.

We can deprecate/delete the bbPress version if they're now equal. It's basically only used internally or via filters.

[johnjamesjacoby]

In 6313:

Common: Update bbp_rel_nofollow_callback() to match latest approach in WordPress.

bbPress continues to have its own version to support this on output vs. pre-save.

Fixes #3067.

[johnjamesjacoby]

In 6328:

Common: Remove nofollow from tests. See #3067.

[johnjamesjacoby]

In 6336:

Use bbp_rel_nofollow() in bbp_make_mentions_clickable_callback(). See #3067.

[johnjamesjacoby]

In 6337:

Use bbp_rel_nofollow() in deprecated bbp_mention_filter() for the sake of parity & coverage. See #3067.

[johnjamesjacoby]

In 6338:

Add bbp_rel_nofollow() to bbp_get_cancel_reply_to_link filter.

Also clean-up bbp_get_cancel_reply_to_link() a bit.

See #3067.