REST API: Avoid fetching each template again to build its links

src/wp-includes/rest-api/endpoints/class-wp-rest-templates-controller.php

@@ -24,6 +24,13 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 	 */
 	protected $post_type;
 
+	/**
+	 * The template being prepared for the response, so prepare_links() can reuse it.
+	 *
+	 * @since 7.2.0
+	 */
+	private ?WP_Block_Template $prepared_template = null;
+
 	/**
 	 * Constructor.
 	 *
@@ -832,7 +839,9 @@ public function prepare_item_for_response( $item, $request ) {
 		$response = rest_ensure_response( $data );
 
 		if ( rest_is_field_included( '_links', $fields ) || rest_is_field_included( '_embedded', $fields ) ) {
-			$links = $this->prepare_links( $template->id );
+			$this->prepared_template = $template;
+			$links                   = $this->prepare_links( $template->id );
+			$this->prepared_template = null;
 			$response->add_links( $links );
 			if ( ! empty( $links['self']['href'] ) ) {
 				$actions = $this->get_available_actions();
@@ -984,7 +993,13 @@ protected function prepare_links( $id ) {
 		);
 
 		if ( post_type_supports( $this->post_type, 'revisions' ) ) {
-			$template = get_block_template( $id, $this->post_type );
+			// Reuse the template being prepared instead of querying it again for each item.
+			if ( $this->prepared_template instanceof WP_Block_Template && $this->prepared_template->id === $id ) {
+				$template = $this->prepared_template;
+			} else {
+				// Only reached when a subclass calls prepare_links() outside of prepare_item_for_response().
+				$template = get_block_template( $id, $this->post_type );
+			}
 			if ( $template instanceof WP_Block_Template && ! empty( $template->wp_id ) ) {
 				$revisions       = wp_get_latest_revision_id_and_total_count( $template->wp_id );
 				$revisions_count = ! is_wp_error( $revisions ) ? $revisions['count'] : 0;

tests/phpunit/tests/rest-api/wpRestTemplatesController.php

@@ -1247,4 +1247,54 @@ public function test_prepare_item_for_database_injects_hooked_block() {
 			'The hooked block was not injected into the anchor block\'s ignoredHookedBlocks metadata.'
 		);
 	}
+
+	/**
+	 * Tests that preparing a collection does not fetch each template again to build its links.
+	 *
+	 * @ticket 66381
+	 *
+	 * @covers WP_REST_Templates_Controller::prepare_links
+	 */
+	public function test_get_items_should_not_refetch_each_template_for_links() {
+		wp_set_current_user( self::$admin_id );
+
+		$mock = new MockAction();
+		add_filter( 'pre_get_block_template', array( $mock, 'filter' ) );
+		$response = rest_get_server()->dispatch( new WP_REST_Request( 'GET', '/wp/v2/templates' ) );
+
+		$this->assertSame( 200, $response->get_status(), 'The request should succeed.' );
+		$this->assertSame( 0, $mock->get_call_count(), 'Templates should not be fetched again to prepare their links.' );
+	}
+
+	/**
+	 * Tests that the version history link of a customized template is kept when preparing a collection.
+	 *
+	 * @ticket 66381
+	 *
+	 * @covers WP_REST_Templates_Controller::prepare_links
+	 */
+	public function test_get_items_should_include_version_history_link_for_customized_template() {
+		wp_set_current_user( self::$admin_id );
+
+		$this->assertIsInt(
+			wp_update_post(
+				array(
+					'ID'           => self::$template_post->ID,
+					'post_content' => 'Content for a revision.',
+				),
+				true
+			)
+		);
+		$revisions = wp_get_latest_revision_id_and_total_count( self::$template_post->ID );
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/templates' );
+		$data    = rest_get_server()->response_to_data( rest_get_server()->dispatch( $request ), false );
+		$item    = $this->find_and_normalize_template_by_id( $data, 'default//my_template' );
+		$found   = wp_list_filter( $data, array( 'id' => 'default//my_template' ) );
+		$links   = array_first( $found )['_links'];
+
+		$this->assertNotEmpty( $item, 'The customized template should be in the collection.' );
+		$this->assertSame( $revisions['count'], $links['version-history'][0]['count'], 'The version history count should match the revisions of the template.' );
+		$this->assertSame( $revisions['latest_id'], $links['predecessor-version'][0]['id'], 'The predecessor version should be the latest revision.' );
+	}
 }