Update check for active cart template and migration routine

src/BlockTemplatesController.php

@@ -835,15 +835,33 @@ protected function migrate_page( $page_id, $page ) {
 			$template_content = $this->get_default_migrate_page_template( $page );
 		}
 
-		$request = new \WP_REST_Request( 'POST', '/wp/v2/templates/woocommerce/woocommerce//' . $page_id );
-		$request->set_body_params(
+		$new_page_template = BlockTemplateUtils::get_block_template( 'woocommerce/woocommerce//' . $page_id, 'wp_template' );
+
+		// Check template validity--template must exist, and custom template must not be present already.
+		if ( ! $new_page_template || $new_page_template->wp_id ) {
+			update_option( 'has_migrated_' . $page_id, '1' );
+			return;
+		}
+
+		$new_page_template_id = wp_insert_post(
 			[
-				'id'      => 'woocommerce/woocommerce//' . $page_id,
-				'content' => $template_content,
-			]
+				'post_name'    => $new_page_template->slug,
+				'post_type'    => 'wp_template',
+				'post_status'  => 'publish',
+				'tax_input'    => array(
+					'wp_theme' => $new_page_template->theme,
+				),
+				'meta_input'   => array(
+					'origin' => $new_page_template->source,
+				),
+				'post_content' => $template_content,
+			],
+			true
 		);
-		rest_get_server()->dispatch( $request );
-		update_option( 'has_migrated_' . $page_id, '1' );
+
+		if ( ! is_wp_error( $new_page_template_id ) ) {
+			update_option( 'has_migrated_' . $page_id, '1' );
+		}
 	}
 
 	/**

src/Templates/CartTemplate.php

@@ -33,7 +33,8 @@ public static function get_placeholder_page() {
 	 */
 	protected function is_active_template() {
 		global $post;
-		return $post instanceof \WP_Post && get_option( 'woocommerce_cart_page_endpoint' ) === $post->post_name;
+		$placeholder = $this->get_placeholder_page();
+		return null !== $placeholder && $post instanceof \WP_Post && $placeholder->post_name === $post->post_name;
 	}
 
 	/**

src/Templates/CheckoutTemplate.php

@@ -42,6 +42,7 @@ public static function get_template_title() {
 	 */
 	public function is_active_template() {
 		global $post;
-		return $post instanceof \WP_Post && get_option( 'woocommerce_checkout_page_endpoint' ) === $post->post_name;
+		$placeholder = $this->get_placeholder_page();
+		return null !== $placeholder && $post instanceof \WP_Post && $placeholder->post_name === $post->post_name;
 	}
 }