Media: Ensure that wp_get_attachment_metadata can return values from the global $post, if avaiable.

In [49084] (for #50679), wp_get_attachment_metadata() was changed to improve performance, but it had the side effect of eliminating the ability to call it with no arguments and have it default to using the global $post.

This change restores that ability, while keeping the performance improvements from the original change.

This changeset brings [50039] to the 5.6 branch.

Fixes #52196.
Props cfinke, hellofromTonya, mukesh27, dilipbheda, Mista-Flo, audrasjb, SergeyBiryukov, whyisjake.

Built from https://develop.svn.wordpress.org/branches/5.6@50040


git-svn-id: http://core.svn.wordpress.org/branches/5.6@49741 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/post.php

@@ -6071,7 +6071,7 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
  *
  * @since 2.1.0
  *
- * @param int  $attachment_id Attachment post ID. Defaults to global $post.
+ * @param int  $attachment_id Attachment post ID. Default 0.
  * @param bool $unfiltered    Optional. If true, filters are not run. Default false.
  * @return array|false {
  *     Attachment metadata. False on failure.
@@ -6087,6 +6087,16 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
 function wp_get_attachment_metadata( $attachment_id = 0, $unfiltered = false ) {
 	$attachment_id = (int) $attachment_id;
 
+	if ( ! $attachment_id ) {
+		$post = get_post();
+
+		if ( ! $post ) {
+			return false;
+		}
+
+		$attachment_id = $post->ID;
+	}
+
 	$data = get_post_meta( $attachment_id, '_wp_attachment_metadata', true );
 
 	if ( ! $data ) {

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6.1-alpha-50038';
+$wp_version = '5.6.1-alpha-50040';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.