Taxonomy: Ensure consistency of `hide_empty` in term queries when `taxonomy` is excluded.

When querying for terms in hierarchical categories using `hide_empty=true`,
results have historically included parent terms which are themselves
unattached to any objects (are "empty") but which have non-empty descendent
terms. Because this process involves walking the descendant tree, we avoid it
when we detect that the queried taxonomies are not hierarchical. (This
behavior was introduced in [5525].)

When the `taxonomy` parameter of `get_terms()` was made optional - see #35495,
[36614] - it affected the mechanism for avoiding unneccessary tree walks,
since there may not be any explicitly declared taxonomies to run through
`is_taxonomy_hierarchical()`. As a result, term queries excluding `taxonomy`
did not check descendants, and empty parents with non-empty children were not
included in `hide_empty` results.

We correct the behavior by crawling term descendants when the `taxonomy`
argument is absent, which means that we're querying for terms in all taxonomies.

Props smerriman.
Fixes #37728.
Built from https://develop.svn.wordpress.org/trunk@45888


git-svn-id: http://core.svn.wordpress.org/trunk@45699 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-term-query.php

@@ -326,6 +326,9 @@ class WP_Term_Query {
 					$has_hierarchical_tax = true;
 				}
 			}
+		} else {
+			// When no taxonomies are provided, assume we have to descend the tree.
+			$has_hierarchical_tax = true;
 		}
 
 		if ( ! $has_hierarchical_tax ) {

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45887';
+$wp_version = '5.3-alpha-45888';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.