Shortcodes: Add a `do_shortcode_tag` filter.

The addition of the `pre_do_shortcode_tag` in [38506] allows plugins to short-circuit the shortcode execution process, which is particularly helpful for caching expensive shortcodes.

The `do_shortcode_tag` is the corresponding part of that system - when a shortcode hasn't been executed previously, there needs to be a clean method of populating the cache.

Props flixos90.
Fixes #32790.


Built from https://develop.svn.wordpress.org/trunk@38713


git-svn-id: http://core.svn.wordpress.org/trunk@38656 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/shortcodes.php

@@ -339,13 +339,21 @@ function do_shortcode_tag( $m ) {
 		return $return;
 	}
 
-	if ( isset( $m[5] ) ) {
-		// enclosing tag - extra parameter
-		return $m[1] . call_user_func( $shortcode_tags[$tag], $attr, $m[5], $tag ) . $m[6];
-	} else {
-		// self-closing tag
-		return $m[1] . call_user_func( $shortcode_tags[$tag], $attr, null,  $tag ) . $m[6];
-	}
+	$content = isset( $m[5] ) ? $m[5] : null;
+
+	$output = $m[1] . call_user_func( $shortcode_tags[ $tag ], $attr, $content, $tag ) . $m[6];
+
+	/**
+	 * Filters the output created by a shortcode callback.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param string $output Shortcode output.
+	 * @param string $tag    Shortcode name.
+	 * @param array  $attr   Shortcode attributes array,
+	 * @param array  $m      Regular expression match array.
+	 */
+	return apply_filters( 'do_shortcode_tag', $output, $tag, $attr, $m );
 }
 
 /**

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38712';
+$wp_version = '4.7-alpha-38713';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.