remove duplicate code in wp_list_filter()

[pbearne]

The code in wp_list_filter() is the same as the code in wp_filter_object_list() with no $field so I have created a patch to wrap wp_filter_object_list removing duplicated code

Trac ticket: https://core.trac.wordpress.org/ticket/53988

[pbearne]

I added tests for this in ticket https://core.trac.wordpress.org/ticket/53987

[SergeyBiryukov]

Thanks for the PR!

It looks like wp_filter_object_list() used to wrap wp_list_filter() before [38928] / #37128.

So I think I would prefer reinstating that, as doing it the other way around would have more unnecessary if ( $field ) checks.

[SergeyBiryukov]

Replying to SergeyBiryukov:

So I think I would prefer reinstating that.

Scratch that, it looks like that would require creating a second WP_List_Util instance, which might have a performance or memory impact, depending on the size of the list.

[SergeyBiryukov]

Some more history here: [14108], [15686], [17427], [38928].

[SergeyBiryukov]

The unit tests for wp_list_filter() ​currently fail with this PR:

There was 1 failure:

1) Tests_Functions_wpListUtil::test_wp_list_filter with data set "invalid operator" (array(stdClass Object (...), stdClass Object (...)), array('bar'), 'XOR', array())
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
+    0 => stdClass Object (...)
+    1 => stdClass Object (...)
 )

/var/www/tests/phpunit/includes/abstract-testcase.php:813
/var/www/tests/phpunit/tests/functions/wpListUtil.php:373

[SergeyBiryukov]

The failure is because WP_List_Util::filter() performs validation of the $operator argument, but in case of an invalid operator it just returns early and does not assign the $this->output value that wp_filter_object_list() returns.

This means that wp_filter_object_list() and wp_list_filter() treat an invalid operator differently:

• wp_filter_object_list() returns the original array.
• wp_list_filter() returns an empty array.

53988.diff​ fixes that and the tests ​seem to pass now, though it might be up for discussion whether the current behavior is a bug or a feature.

[hellofromTonya]

In reviewing and testing 53988.diff​, @SergeyBiryukov I think you did resolve an issue. Bailing out without resetting the $output property to an empty array means WP_List_Util::get_output() may not be in the right state when invoked. This was why the tests were failing.

The patch looks good to me. Marking it for commit.

[hellofromTonya]

In 52066:

General: Convert wp_list_filter() into a wrapper for wp_filter_object_list().

The code in wp_list_filter() was a duplicate of wp_filter_object_list(), minus the WP_List_Util::pluck() (used when $field is configured).

In testing the wrapper, discovered an edge case (and potential bug) in WP_List_Util::filter() where if the operator matches an empty array was returned without resetting the output property. Without that property being set correctly, WP_List_Util::get_output() was not correct. This commit also fixes this by resetting the property to an empty array.

Follow-up to [15686], [17427], [38928], [51044].

Props pbearne, sergeybiryukov, hellofromTonya.
Fixes #53988.

Closing as the alternate patch was committed via changeset https://core.trac.wordpress.org/changeset/52066.

[hellofromTonya]

Thank you @pbearne and @SergeyBiryukov for your contributions to improving Core's codebase!