CRM-19665 Canonical URL for WP basepage pages is the basepage itself

Maybe someday we'll establish a firm list of params that might be expected on a frontend URL, and we could also establish a canonical order of params. This would help say, for example, that
http://example.org/civicrm/?page=CiviCRM&q=civicrm/event/register&reset=1&id=1&cid=0
is based upon the canonical URL
http://example.org/civicrm/?page=CiviCRM&q=civicrm/event/register&id=1&reset=1

But until then, we can at the very least provide the whole query string and set the official basepage.

Andrew Hunt Do we want to test for the version of WP we are on before loading the filter?
I am also reluctant to start incuding filters for specific plugins. I'd prefer to leave it up the the developer. If we add Yoast's (35 million downloads) do we also make sure we work with All in One SEO (30 million downloads)? I would think it best to leave adding plugin specific filters to the developer. Ehat do you think?

Do you know what happens if you add a filter for something that doesn't exist yet? I'm totally happy to add a version check if you think it makes a difference.

Re: Yoast, I agree in general. In this case, though, Yoast's filter predates the core filter and totally bypasses it. Yes, that's Yoast's fault, but it still has only been a little while since the other filter is out. If All in One is in the same boat (longstanding filter that's incompatible with get_canonical_url), I would also be in favor of working with that.

My $0.02: I agree entirely with Andrew, both on adding the WP 4.6 filter as is and supporting third party plugins. The CiviCRM plugin already has support for the Yoast plugin's Open Graph title. Further support where required seems sensible.

From all I can tell (testing and docs) adding a filter where it does not exist is a soft fail. I had expected a Warning, but not seeing any in my logs.

If we are going to do 3rd party support, I would definitely want All In One SEO (AIOSEO) support added.

We can do that by adding

     // All in One SEO has separate way of establishing canonical URL
    add_filter( 'aioseop_canonical_url', array($this, 'basepage_canonical_url' ), 999);

I've tested the patch with no SEO plugin, Yoast and AIOSEO and it works in all three cases. The original patch won't cover if AIOSEO is installed.

Kevin Cristiano OT: it's a feature not a bug. If only more plugins would offer actions for their functionality instead of providing functions, then it all those endless

if ( function_exists( 'some_plugin_function' ) ) { some_plugin_function() }

tests could be replaced with

do_action( 'some_plugin_action' )

I added the AIOSEO line, the param in the docblock, and a bunch of spaces everywhere. (I like to use the phpcs plugin in Atom, but it freaks out if you use the WordPress standard on this file because all of the lines are space-indented--you can't see the real problems among them.)

tagged for 4.7.17.

Tested again against current master branches, works propoerly. Tested with Yoast SEO, AIOSEO and with no SEO plugin. Works in all conditions.

I consider this a bug fix, and would like to see in 4.7.17