Issue #841: Make remove_embed() add previous shortcode.

On Weston's suggestion.
This function should return the shortcode
to the state before this embed handler changed it.
So it stores the previous callback in $removed_shortcode.
And it adds that callback in remove_embed().

includes/embeds/class-amp-playlist-embed-handler.php

@@ -18,7 +18,7 @@ class AMP_Playlist_Embed_Handler extends AMP_Base_Embed_Handler {
 	/**
 	 * The tag of the shortcode.
 	 *
-	 * @var string.
+	 * @var string
 	 */
 	const SHORTCODE = 'playlist';
 
@@ -28,21 +28,21 @@ class AMP_Playlist_Embed_Handler extends AMP_Base_Embed_Handler {
 	 * This corresponds to the max-width in wp-mediaelement.css:
 	 * .wp-playlist .wp-playlist-current-item img
 	 *
-	 * @var string.
+	 * @var string
 	 */
 	const THUMB_MAX_WIDTH = 60;
 
 	/**
 	 * The height of the carousel.
 	 *
-	 * @var string.
+	 * @var string
 	 */
 	const CAROUSEL_HEIGHT = 160;
 
 	/**
 	 * The pattern to get the playlist data.
 	 *
-	 * @var string.
+	 * @var string
 	 */
 	const PLAYLIST_REGEX = ':<script type="application/json" class="wp-playlist-script">(.+?)</script>:s';
 
@@ -53,6 +53,13 @@ class AMP_Playlist_Embed_Handler extends AMP_Base_Embed_Handler {
 	 */
 	public static $playlist_id = 0;
 
+	/**
+	 * The removed shortcode callback.
+	 *
+	 * @var string|array
+	 */
+	public $removed_shortcode;
+
 	/**
 	 * The parsed data for the playlist.
 	 *
@@ -62,8 +69,15 @@ class AMP_Playlist_Embed_Handler extends AMP_Base_Embed_Handler {
 
 	/**
 	 * Registers the playlist shortcode.
+
+	 * @global array $shortcode_tags
+	 * @return void
 	 */
 	public function register_embed() {
+		global $shortcode_tags;
+		if ( shortcode_exists( self::SHORTCODE ) ) {
+			$this->removed_shortcode = $shortcode_tags[ self::SHORTCODE ];
+		}
 		add_shortcode( self::SHORTCODE, array( $this, 'shortcode' ) );
 		add_action( 'wp_enqueue_scripts', array( $this, 'styling' ) );
 	}
@@ -74,7 +88,7 @@ public function register_embed() {
 	 * @return void
 	 */
 	public function unregister_embed() {
-		remove_shortcode( self::SHORTCODE );
+		add_shortcode( self::SHORTCODE, $this->removed_shortcode );
 	}
 
 	/**

tests/test-class-amp-playlist-embed-handler.php

@@ -58,12 +58,13 @@ public function tearDown() {
 	 */
 	public function test_register_embed() {
 		global $shortcode_tags;
-		$shortcode = 'playlist';
-		$this->assertFalse( isset( $shortcode_tags[ $shortcode ] ) );
+		$removed_shortcode = 'wp_playlist_shortcode';
+		add_shortcode( 'playlist', $removed_shortcode );
 		$this->instance->register_embed();
-		$this->assertEquals( 'AMP_Playlist_Embed_Handler', get_class( $shortcode_tags[ $shortcode ][0] ) );
-		$this->assertEquals( 'shortcode', $shortcode_tags[ $shortcode ][1] );
+		$this->assertEquals( 'AMP_Playlist_Embed_Handler', get_class( $shortcode_tags[ AMP_Playlist_Embed_Handler::SHORTCODE ][0] ) );
+		$this->assertEquals( 'shortcode', $shortcode_tags[ AMP_Playlist_Embed_Handler::SHORTCODE ][1] );
 		$this->assertEquals( 10, has_action( 'wp_enqueue_scripts', array( $this->instance, 'styling' ) ) );
+		$this->assertEquals( $removed_shortcode, $this->instance->removed_shortcode );
 		$this->instance->unregister_embed();
 	}
 
@@ -74,9 +75,10 @@ public function test_register_embed() {
 	 */
 	public function test_unregister_embed() {
 		global $shortcode_tags;
-		$shortcode = 'playlist';
+		$expected_removed_shortcode        = 'wp_playlist_shortcode';
+		$this->instance->removed_shortcode = $expected_removed_shortcode;
 		$this->instance->unregister_embed();
-		$this->assertFalse( isset( $shortcode_tags[ $shortcode ] ) );
+		$this->assertEquals( $expected_removed_shortcode, $shortcode_tags[ AMP_Playlist_Embed_Handler::SHORTCODE ] );
 	}
 
 	/**