Framework: Add support for dynamic templates

lib/load.php

@@ -20,6 +20,7 @@
 require dirname( __FILE__ ) . '/i18n.php';
 require dirname( __FILE__ ) . '/parser.php';
 require dirname( __FILE__ ) . '/register.php';
+require dirname( __FILE__ ) . '/template.php';
 
 // Register server-side code for individual blocks.
 foreach ( glob( dirname( __FILE__ ) . '/../blocks/library/*/index.php' ) as $block_logic ) {

lib/template.php

@@ -0,0 +1,228 @@
+<?php
+/**
+ * Dynamic template registration and overrides.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Returns true if the passed template name is for a dynamic template, or false
+ * otherwise. A template is considered dynamic if it is not a file path, and
+ * rather the slug of a template post.
+ *
+ * @param string $template The path or slug of the template to test.
+ *
+ * @return bool Whether the template is dynamic.
+ */
+function gutenberg_is_dynamic_template( $template ) {
+	return 1 !== preg_match( '/\.php$/', $template );
+}
+
+/**
+ * Replaces the output content of the template with the post content of a
+ * dynamic template, if it is the result of a dynamic template override.
+ *
+ * @see wp-includes/template-loader.php
+ *
+ * @param string $template The path or slug of the template to include.
+ */
+function gutenberg_template_include( $template ) {
+	// Assume if template override resulted in no dynamic template result, that
+	// original should be used.
+	if ( ! gutenberg_is_dynamic_template( $template ) ) {
+		return $template;
+	}
+
+	$template_post_query = new WP_Query( array(
+		'name'      => $template,
+		'post_type' => 'wp_template',
+	) );
+
+	// Abort and fall through to theme error messages.
+	if ( ! $template_post_query->have_posts() ) {
+		return;
+	}
+
+	$template_posts = $template_post_query->get_posts();
+	$template_post  = $template_posts[0];
+
+	echo apply_filters( 'the_content', $template_post->post_content );
+
+	// End of page lifecycle, abort to prevent theme error messages.
+	exit;
+}
+add_filter( 'template_include', 'gutenberg_template_include' );
+
+/**
+ * Given a template path, returns a template name with file extension removed.
+ *
+ * @param string $template_name The path of the template.
+ *
+ * @return string The name of the template with path extension removed.
+ */
+function gutenberg_get_template_slug( $template_name ) {
+	return preg_replace( '/\.php$/', '', $template_name );
+}
+
+/**
+ * Overrides template lookup to consider whether any dynamic templates exist,
+ * and if the priority for that template in the hierarchy is higher, uses it in
+ * place of the original discovered template.
+ *
+ * @param string $template  Path to the template. See locate_template().
+ * @param string $type      Filename without extension.
+ * @param array  $templates A list of template candidates, in descending order of priority.
+ *
+ * @return string Path to the template file or slug of the dynamic template.
+ */
+function gutenberg_override_template( $template, $type, $templates ) {
+	// Determine original priority of the default discovered template to avoid
+	// overriding if the dynamic template is of lower priority. Template may be
+	// an empty string if one is not loaded.
+	$original_priority = PHP_INT_MAX;
+	if ( $template ) {
+		for ( $i = 0; $i < count( $templates ); $i++ ) {
+			$template_name = $templates[ $i ];
+
+			// If post is explicitly assigned a dynamic template, return immediately.
+			if ( gutenberg_is_dynamic_template( $template_name ) ) {
+				return $template_name;
+			}
+
+			// `$template` filter value is an absolute path, so check that
+			// template file exists at end of path.
+			$is_template = ( 0 === substr_compare(
+				$template,
+				'/' . $template_name,
+				( -1 * strlen( $template_name ) ) - 1
+			) );
+
+			if ( $is_template ) {
+				$original_priority = $i;
+				break;
+			}
+		}
+	}
+
+	// Prepare template paths for slug lookup.
+	$override_templates = array_map( 'gutenberg_get_template_slug', $templates );
+
+	$candidate_template_posts_query = new WP_Query( array(
+		'post_name__in' => $override_templates,
+		'post_type'     => 'wp_template',
+	) );
+
+	if ( ! $candidate_template_posts_query->have_posts() ) {
+		return $template;
+	}
+
+	$candidate_template_posts = $candidate_template_posts_query->get_posts();
+	$override_template        = $candidate_template_posts[0]->post_name;
+	$override_priority        = array_search( $override_template, $override_templates );
+
+	// Override template if priority is higher.
+	if ( $override_priority <= $original_priority ) {
+		$template = $override_template;
+	}
+
+	return $template;
+}
+
+/**
+ * Array of all override-able default template types.
+ *
+ * @see get_query_template
+ *
+ * @var array
+ */
+$template_types = array(
+	'index',
+	'404',
+	'archive',
+	'author',
+	'category',
+	'tag',
+	'taxonomy',
+	'date',
+	'embed',
+	'home',
+	'frontpage',
+	'page',
+	'paged',
+	'search',
+	'single',
+	'singular',
+	'attachment',
+);
+
+foreach ( $template_types as $template_type ) {
+	add_filter( $template_type . '_template', 'gutenberg_override_template', 20, 3 );
+}
+
+/**
+ * Merges discovered post templates with those available by matching taxonomy
+ * of dynamic templates.
+ *
+ * @param array        $templates Array of post templates. Keys are filenames,
+ *                                values are translated names.
+ * @param WP_Theme     $theme     The theme object.
+ * @param WP_Post|null $post      The post being edited, provided for context, or null.
+ * @param string       $post_type Post type to get the templates for.
+ *
+ * @return string Post templates, including dynamic templates.
+ */
+function gutenberg_templates( $templates, $theme, $post, $post_type ) {
+	$templates_query = new WP_Query( array(
+		'post_type' => 'wp_template',
+		'tax_query' => array(
+			array(
+				'taxonomy' => 'wp_template_post_types',
+				'field'    => 'slug',
+				'terms'    => $post_type,
+			),
+		),
+	) );
+
+	foreach ( $templates_query->get_posts() as $template ) {
+		$templates[ $template->post_name ] = $template->post_title;
+	}
+
+	return $templates;
+}
+
+/**
+ * Adds filters to override available templates for all post types.
+ */
+function gutenberg_filter_post_type_templates() {
+	$post_types = get_post_types();
+	foreach ( $post_types as $post_type ) {
+		$filter_tag = sprintf( 'theme_%s_templates', $post_type );
+		add_filter( $filter_tag, 'gutenberg_templates', 10, 4 );
+	}
+}
+add_action( 'init', 'gutenberg_filter_post_type_templates', 20 );
+
+/**
+ * Registers post tyes and taxonomies for dynamic templates.
+ */
+function gutenberg_register_template_post_types() {
+	register_post_type( 'wp_template', array(
+		'public'       => true,
+		'menu_icon'    => 'dashicons-layout',
+		'show_in_rest' => true,
+		'supports'     => array( 'title', 'editor' ),
+		'labels'       => array(
+			'name' => __( 'Templates', 'gutenberg' ),
+		),
+	) );
+
+	register_taxonomy( 'wp_template_post_types', 'wp_template', array(
+		'public'       => true,
+		'show_in_rest' => true,
+		'show_in_menu' => false,
+		'labels'       => array(
+			'name' => __( 'Post Types', 'gutenberg' ),
+		),
+	) );
+}
+add_action( 'init', 'gutenberg_register_template_post_types' );