The "{$taxonomy}_children" cache can become stale

[dd32]

When you add multiple hierarchical terms on a single page load, "{$taxonomy}_children" can become stale as only the first call to clean_term_cache() will invalidate that cache.

On subsequent calls, it, along with the all_ids and get taxonomy caches will not be cleared, which leads to anything which relies upon hierarchical checks to fail.
Many things rely upon the hierarchical cache, retrieving children of terms being the primary one.

This can be traced to the static $cleaned added in [9102].

I've attached a basic unit test that covers "{$taxonomy}_children" via _get_term_hierarchy() in 25711.diff​

[nacin]

Related ticket, referring to {$taxonomy}_relationships stale cache: #24189.

[wonderboymusic]

Fixed via [27102].

[bpetty]

I'm not sure exactly what values should be tested for here, so I'm not going to attempt a patch, but this does need some eyes on the unit tests again at least.

1) Tests_Term_Cache::test_category_children_cache
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    75 => Array (...)
 )

/vagrant/wordpress/tests/phpunit/tests/term/cache.php:22

Here's the assertion:

$this->assertEquals( array( $term_id1 => array( $term_id1_child ) ), $hierarchy );

I've only see this fail on PHP 5.2, however, what I'd like to specifically point out is that this is comparing the result fetched from the factory, which should contain row IDs, and likely a bunch more data that is both irrelevant to this test, and is also volatile (can easily change between runs just like the ID does depending on previous tests run - try running full tests compared to just --group taxonomy).

This really needs to be rewritten with more more specific values used for assertion checks. Try to avoid using arrays, they can frequently fail when just out of order (but still remain functional and correct). In fact, don't even use the variable returned from the factory. Use an entirely explicit static array. We still need to know *exactly* what the test should be returning in case the test is failing (like it is here).

[SergeyBiryukov]

Related: #14485

[SergeyBiryukov]

The changes suggested in 25711.diff​ were committed in [27163] and [27103].

Unit test failure is not directly related to those commits, see ticket:14485:95. Let's fix it in #14485.