Editor: Resolve template request `?_wp-find-template=true` for new posts and pages.

The template resolution system makes a request like `/?page_id=1234&_wp-find-template=true`, depending on `WP_Query` to resolve a page or post using the page_id or p (post_id) in the query string. With new posts/pages, a placeholder post with the status auto-draft is created. But by default `WP_Query` will not resolve these posts, unless the query is specifically set to look for them.

This commit handles the query string to properly resolve a page or post. It adds 2 private callbacks for the processing.

Props poena, noisysocks, bernhard-reiter, costdev, hellofromTonya.
Fixes #54553.
Built from https://develop.svn.wordpress.org/trunk@52316


git-svn-id: http://core.svn.wordpress.org/trunk@51908 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-template.php

@@ -5,6 +5,32 @@
  * @package WordPress
  */
 
+/**
+ * Adds necessary filters to use 'wp_template' posts instead of theme template files.
+ *
+ * @access private
+ * @since 5.9.0
+ */
+function _add_template_loader_filters() {
+	if ( ! current_theme_supports( 'block-templates' ) ) {
+		return;
+	}
+
+	$template_types = array_keys( get_default_block_template_types() );
+	foreach ( $template_types as $template_type ) {
+		// Skip 'embed' for now because it is not a regular template type.
+		if ( 'embed' === $template_type ) {
+			continue;
+		}
+		add_filter( str_replace( '-', '', $template_type ) . '_template', 'locate_block_template', 20, 3 );
+	}
+
+	// Request to resolve a template.
+	if ( isset( $_GET['_wp-find-template'] ) ) {
+		add_filter( 'pre_get_posts', '_resolve_template_for_new_post' );
+	}
+}
+
 /**
  * Find a block template with equal or higher specificity than a given PHP template file.
  *
@@ -266,3 +292,35 @@ function _block_template_render_without_post_block_context( $context ) {
 
 	return $context;
 }
+
+/**
+ * Sets the current WP_Query to return auto-draft posts.
+ *
+ * The auto-draft status indicates a new post, so allow the the WP_Query instance to
+ * return an auto-draft post for template resolution when editing a new post.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param WP_Query $wp_query Current WP_Query instance, passed by reference.
+ */
+function _resolve_template_for_new_post( $wp_query ) {
+	remove_filter( 'pre_get_posts', '_resolve_template_for_new_post' );
+
+	// Pages.
+	$page_id = isset( $wp_query->query['page_id'] ) ? $wp_query->query['page_id'] : null;
+
+	// Posts, including custom post types.
+	$p = isset( $wp_query->query['p'] ) ? $wp_query->query['p'] : null;
+
+	$post_id = $page_id ? $page_id : $p;
+	$post    = get_post( $post_id );
+
+	if (
+		$post &&
+		'auto-draft' === $post->post_status &&
+		current_user_can( 'edit_post', $post->ID )
+	) {
+		$wp_query->set( 'post_status', 'auto-draft' );
+	}
+}

wp-includes/default-filters.php

@@ -680,5 +680,6 @@ add_filter( 'pre_wp_unique_post_slug', 'wp_filter_wp_template_unique_post_slug',
 add_action( 'save_post_wp_template_part', 'wp_set_unique_slug_on_create_template_part' );
 add_action( 'wp_footer', 'the_block_template_skip_link' );
 add_action( 'setup_theme', 'wp_enable_block_templates' );
+add_action( 'wp_loaded', '_add_template_loader_filters' );
 
 unset( $filter, $action );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-beta1-52315';
+$wp_version = '5.9-beta1-52316';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.