Taxonomy: Don't discard keys when merging queried terms from different taxonomies.

For values of `fields` like `id=>parent`, the keys of the array must be
maintained as part of the query results.

Introduced as part of #40496. See [38667], [40513].

Props miyauchi, dany2217, pcarvalho.
Fixes #41293.
Built from https://develop.svn.wordpress.org/trunk@41809


git-svn-id: http://core.svn.wordpress.org/trunk@41643 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/taxonomy.php

@@ -1912,7 +1912,14 @@ function wp_get_object_terms($object_ids, $taxonomies, $args = array()) {
 
 	// Taxonomies registered without an 'args' param are handled here.
 	if ( ! empty( $taxonomies ) ) {
-		$terms = array_merge( $terms, get_terms( $args ) );
+		$terms_from_remaining_taxonomies = get_terms( $args );
+
+		// Array keys should be preserved for values of $fields that use term_id for keys.
+		if ( ! empty( $args['fields'] ) && 0 === strpos( $args['fields'], 'id=>' ) ) {
+			$terms = $terms + $terms_from_remaining_taxonomies;
+		} else {
+			$terms = array_merge( $terms, $terms_from_remaining_taxonomies );
+		}
 	}
 
 	/**

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-beta1-41808';
+$wp_version = '4.9-beta1-41809';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.