Fix possible discrepancy in author search with ignored authors

[TheCrowned]

This fixes #273.

The issue was that, in some cases, it was possible to add the same author more than once. Even though it was already a co-author of the post, it would still show up in search and be available for another addition - here, the last suggestion is the same user who is already an author of the post:

tl;dr - the issue was due to JS referencing existing authors by user_nicename while PHP by user_login.

Getting a peak at what happened when a post is saved, it was clear that there was some mismatch between the newly-added coauthors and the already present ones. It looked like some case issue:

I expected this to be an issue with search_authors() - in particular, something to do with $ignored_authors. Indeed, diving into the JS and PHP, I found out it was an issue with how ignored authors are handled by the two sides.

JS takes care of making the AJAX request to ajax_suggest(), which in turn calls search_authors(). It sends existing_authors as parameter, populating it with current authors user_nicenames.

function coauthors_create_author_hidden_input ( author ) {
	var input = jQuery( '<input />' )
		.attr({
			'type': 'hidden',
			'id': 'coauthors_hidden_input',
			'name': 'coauthors[]',
			'value': decodeURIComponent( author.nicename )
		});
	return input;
}

jQuery( document ).ajaxSend(function( e, xhr, settings ) {
	var existing_authors = jQuery( 'input[name="coauthors[]"]' ).map(function(){return jQuery( this ).val();}).get();

But on the other side, PHP was deciding whether an author should be excluded from search comparing user_logins with the AJAX-supplied list of user_nicenames. This would work fine in several situations - basically, all the times user_login did not have any special chars or uppercase letters. But when user_nicename was different from user_login, this was clearly an issue.

$found_users[ $found_user->user_login ] = $found_user;

foreach ( $found_users as $key => $found_user ) {
	if ( in_array( $found_user->user_login, $ignored_authors ) ) { 
		unset( $found_users[ $key ] );
	}
}

I thus changed user_login with user_nicename in the PHP bit. After this edit, the issue has gone! :)

This edit does not affect anything else, as far as I am been able to check. All PHPUnit tests still succeed as they did before. Also, search_authors() is only called by ajax_suggest(), so it should really only affect its behavior (and that's what my tests have confirmed) :)

[TheCrowned]

Also updated tests to search_authors() to work with this edit.

[sboisvert]

lgtm. Great work on this, Love the explanations and the screenshot. It makes it really easy to follow along and know that this fix is a great one. Thanks!

[mdbitz]

Pending @philipjohn for Merge or feedback.

[sboisvert]

@rebeccahum want to give this a glance? If you think we're good with it let's merge it.

cc @philipjohn in case you have thoughts on it.

[garretthyder]

Thanks for taking the time to address my issue guys. I appreciate the thorough recon and explanation provided by @TheCrowned