Media: Add an action for `wp_media_attach_action`.

This action fires when media is attached/detached from a post.

Fixes: #49614.
Props: jonoaldersonwp, antpb, rebasaurus, donmhico. 


Built from https://develop.svn.wordpress.org/trunk@47909


git-svn-id: http://core.svn.wordpress.org/trunk@47683 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/media.php

@@ -3724,13 +3724,24 @@ function wp_media_attach_action( $parent_id, $action = 'attach' ) {
 		} else {
 			$result = $wpdb->query( "UPDATE $wpdb->posts SET post_parent = 0 WHERE post_type = 'attachment' AND ID IN ( $ids_string )" );
 		}
-
-		foreach ( $ids as $att_id ) {
-			clean_attachment_cache( $att_id );
-		}
 	}
 
 	if ( isset( $result ) ) {
+		foreach ( $ids as $att_id ) {
+			/**
+			 * Fires when media is attached/detached from a post.
+			 *
+			 * @since 5.5
+			 *
+			 * @param string $action    Attach/detach action.
+			 * @param int    $att_id    The attachment ID.
+			 * @param int    $parent_id Attachment parent ID.
+			 */
+			do_action( 'wp_media_attach_action', $action, $att_id, $parent_id );
+
+			clean_attachment_cache( $att_id );
+		}
+
 		$location = 'upload.php';
 		$referer  = wp_get_referer();
 

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-47908';
+$wp_version = '5.5-alpha-47909';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.