[wp-hackers] meta_query orderby bug

[Hameedullah Khan]

Hello Everyone,

So this is my first bug that I was about to report. Then I read that I
should discuss this on #IRC or on mailing list. This is the first time
I am reporting a bug so please bare with me. :) Let me just describe
you the issue.

If we specify meta_key and an orderby query var. The way wordpress
handles them is that it adds them to the meta_query query var which is
an array of array. Wordpress adds new meta_query array to existing
meta_query arrays but the new array as inserted as the first element.

For example if I specified following:
$meta_key = 'priority';
$orderby = 'meta_value_num';
$meta_query = array(
    array(
      'key' => 'weight',
      'value' => 2,
      'compare' => '>=',
      'type' => 'NUMERIC'
   )
);

Then after Wordpress completes parsing the meta_query in function
_parse_meta_query at line #458 in file: wp-includes/meta.php The
resulting meta_query looks like following:
$meta_key = 'priority';
$orderby = 'meta_value_num';
$meta_query = array(
    array(
      'key' => 'priority'
    ),
    array(
      'key' => 'weight',
      'value' => 2,
      'compare' => '>=',
      'type' => 'NUMERIC'
   )
);


This all works fine if I have specified my meta_query and orderby
query vars before the pre_get_posts filter is run. But if I add
orderyby and meta_key in pre_get_posts filter then when WordPress
parses the meta_query again, instead of inserting the new array as the
first element it appends the new array to existing meta_query. And the
resulting meta_query looks like following:

$meta_query = array(
    array(
      'key' => 'weight',
      'value' => 2,
      'compare' => '>=',
      'type' => 'NUMERIC'
   ),
    array(
      'key' => 'priority'
    )
);

And when the meta_sql is generated the orderby is applied to the first
meta key value specified in meta_query. The problematic line is #2470
in wp-includes/query.php which is:

$q['meta_query'] = array_merge( $_meta_query, $q['meta_query'] );

But it should be:

$q['meta_query'] = array_merge( $q['meta_query'], $_meta_query );

So, is it really a bug? Should I report it on trac and be proud of it?
Or this is intended behavior?

-- 
Regards
Hameedullah Khan

w: http://hameedullah.com
t: @hameedullah