Bootstrap/Load: Make handling the /favicon.ico requests more flexible.

Previously, `wp_favicon_request()` was introduced in [13205] to avoid a performance hit of serving a full 404 page on every favicon request.

While working as intended, that implementation did not provide a way for theme or plugin authors to manage the behavior of favicon requests.

This changeset implements the following logic (only applied if WordPress is installed in the root directory):

* If there is a Site Icon set in Customizer, redirect `/favicon.ico` requests to that icon.
* Otherwise, use the WordPress logo as a default icon.
* If a physical `/favicon.ico` file exists, do nothing, let the server handle the request.

Handling `/favicon.ico` is now more consistent with handling `/robots.txt` requests.

New functions and hooks:

* Introduce `is_favicon()` conditional tag to complement `is_robots()`.
* Introduce `do_favicon` action to complement `do_robots` and use it in template loader.
* Introduce `do_favicon()` function, hooked to the above action by default, to complement `do_robots()`.
* Introduce `do_faviconico` action to complement `do_robotstxt`, for plugins to override the default behavior.
* Mark `wp_favicon_request()` as deprecated in favor of `do_favicon()`.

Props jonoaldersonwp, birgire, joostdevalk, mukesh27, SergeyBiryukov.
Fixes #47398.

git-svn-id: https://develop.svn.wordpress.org/trunk@47018 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/canonical.php

@@ -19,8 +19,8 @@
  *
  * Prevents redirection for feeds, trackbacks, searches, and
  * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
- * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
+ * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
- * requests.
+ * or on POST requests.
  *
  * Will also attempt to find the correct link when a user enters a URL that does
  * not exist based on exact WordPress query. Will instead try to parse the URL
@@ -56,7 +56,7 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 		}
 	}
 
-	if ( is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || ( $is_IIS && ! iis7_supports_permalinks() ) ) {
+	if ( is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || is_favicon() || ( $is_IIS && ! iis7_supports_permalinks() ) ) {
 		return;
 	}
 

src/wp-includes/class-wp-query.php

@@ -390,6 +390,14 @@ class WP_Query {
 	 */
 	public $is_robots = false;
 
+	/**
+	 * Signifies whether the current query is for the favicon.ico file.
+	 *
+	 * @since 5.4.0
+	 * @var bool
+	 */
+	public $is_favicon = false;
+
 	/**
 	 * Signifies whether the current query is for the page_for_posts page.
 	 *
@@ -478,6 +486,7 @@ class WP_Query {
 		$this->is_attachment        = false;
 		$this->is_singular          = false;
 		$this->is_robots            = false;
+		$this->is_favicon           = false;
 		$this->is_posts_page        = false;
 		$this->is_post_type_archive = false;
 	}
@@ -744,6 +753,8 @@ class WP_Query {
 
 		if ( ! empty( $qv['robots'] ) ) {
 			$this->is_robots = true;
+		} elseif ( ! empty( $qv['favicon'] ) ) {
+			$this->is_favicon = true;
 		}
 
 		if ( ! is_scalar( $qv['p'] ) || $qv['p'] < 0 ) {
@@ -957,7 +968,9 @@ class WP_Query {
 			$this->is_comment_feed = true;
 		}
 
-		if ( ! ( $this->is_singular || $this->is_archive || $this->is_search || $this->is_feed || ( defined( 'REST_REQUEST' ) && REST_REQUEST ) || $this->is_trackback || $this->is_404 || $this->is_admin || $this->is_robots ) ) {
+		if ( ! ( $this->is_singular || $this->is_archive || $this->is_search || $this->is_feed
+				|| ( defined( 'REST_REQUEST' ) && REST_REQUEST )
+				|| $this->is_trackback || $this->is_404 || $this->is_admin || $this->is_robots || $this->is_favicon ) ) {
 			$this->is_home = true;
 		}
 
@@ -4007,7 +4020,7 @@ class WP_Query {
 	}
 
 	/**
-	 * Is the query for the robots file?
+	 * Is the query for the robots.txt file?
 	 *
 	 * @since 3.1.0
 	 *
@@ -4017,6 +4030,17 @@ class WP_Query {
 		return (bool) $this->is_robots;
 	}
 
+	/**
+	 * Is the query for the favicon.ico file?
+	 *
+	 * @since 5.4.0
+	 *
+	 * @return bool
+	 */
+	public function is_favicon() {
+		return (bool) $this->is_favicon;
+	}
+
 	/**
 	 * Is the query for a search?
 	 *

src/wp-includes/class-wp-rewrite.php

@@ -1259,10 +1259,13 @@ class WP_Rewrite {
 			return $rewrite;
 		}
 
-		// robots.txt -only if installed at the root
+		// robots.txt -- only if installed at the root
 		$home_path      = parse_url( home_url() );
 		$robots_rewrite = ( empty( $home_path['path'] ) || '/' == $home_path['path'] ) ? array( 'robots\.txt$' => $this->index . '?robots=1' ) : array();
 
+		// favicon.ico -- only if installed at the root
+		$favicon_rewrite = ( empty( $home_path['path'] ) || '/' == $home_path['path'] ) ? array( 'favicon\.ico$' => $this->index . '?favicon=1' ) : array();
+
 		// Old feed and service files.
 		$deprecated_files = array(
 			'.*wp-(atom|rdf|rss|rss2|feed|commentsrss2)\.php$' => $this->index . '?feed=old',
@@ -1419,9 +1422,9 @@ class WP_Rewrite {
 
 		// Put them together.
 		if ( $this->use_verbose_page_rules ) {
-			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $page_rewrite, $post_rewrite, $this->extra_rules );
+			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $favicon_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $page_rewrite, $post_rewrite, $this->extra_rules );
 		} else {
-			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $post_rewrite, $page_rewrite, $this->extra_rules );
+			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $favicon_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $post_rewrite, $page_rewrite, $this->extra_rules );
 		}
 
 		/**

src/wp-includes/class-wp.php

@@ -14,7 +14,7 @@ class WP {
 	 * @since 2.0.0
 	 * @var string[]
 	 */
-	public $public_query_vars = array( 'm', 'p', 'posts', 'w', 'cat', 'withcomments', 'withoutcomments', 's', 'search', 'exact', 'sentence', 'calendar', 'page', 'paged', 'more', 'tb', 'pb', 'author', 'order', 'orderby', 'year', 'monthnum', 'day', 'hour', 'minute', 'second', 'name', 'category_name', 'tag', 'feed', 'author_name', 'pagename', 'page_id', 'error', 'attachment', 'attachment_id', 'subpost', 'subpost_id', 'preview', 'robots', 'taxonomy', 'term', 'cpage', 'post_type', 'embed' );
+	public $public_query_vars = array( 'm', 'p', 'posts', 'w', 'cat', 'withcomments', 'withoutcomments', 's', 'search', 'exact', 'sentence', 'calendar', 'page', 'paged', 'more', 'tb', 'pb', 'author', 'order', 'orderby', 'year', 'monthnum', 'day', 'hour', 'minute', 'second', 'name', 'category_name', 'tag', 'feed', 'author_name', 'pagename', 'page_id', 'error', 'attachment', 'attachment_id', 'subpost', 'subpost_id', 'preview', 'robots', 'favicon', 'taxonomy', 'term', 'cpage', 'post_type', 'embed' );
 
 	/**
 	 * Private query variables.
@@ -659,8 +659,8 @@ class WP {
 			return;
 		}
 
-		// Never 404 for the admin, robots, or if we found posts.
+		// Never 404 for the admin, robots, favicon, or if we found posts.
-		if ( is_admin() || is_robots() || $wp_query->posts ) {
+		if ( is_admin() || is_robots() || is_favicon() || $wp_query->posts ) {
 
 			$success = true;
 			if ( is_singular() ) {

src/wp-includes/default-filters.php

@@ -338,6 +338,7 @@ add_action( 'do_feed_rss2', 'do_feed_rss2', 10, 1 );
 add_action( 'do_feed_atom', 'do_feed_atom', 10, 1 );
 add_action( 'do_pings', 'do_all_pings', 10, 0 );
 add_action( 'do_robots', 'do_robots' );
+add_action( 'do_favicon', 'do_favicon' );
 add_action( 'set_comment_cookies', 'wp_set_comment_cookies', 10, 3 );
 add_action( 'sanitize_comment_cookies', 'sanitize_comment_cookies' );
 add_action( 'admin_print_scripts', 'print_emoji_detection_script' );

src/wp-includes/functions.php

@@ -1636,6 +1636,23 @@ function do_robots() {
 	echo apply_filters( 'robots_txt', $output, $public );
 }
 
+/**
+ * Display the favicon.ico file content.
+ *
+ * @since 5.4.0
+ */
+function do_favicon() {
+	/**
+	 * Fires when serving the favicon.ico file.
+	 *
+	 * @since 5.4.0
+	 */
+	do_action( 'do_faviconico' );
+
+	wp_redirect( get_site_icon_url( 32, admin_url( 'images/w-logo-blue.png' ) ) );
+	exit;
+}
+
 /**
  * Determines whether WordPress is already installed.
  *

src/wp-includes/load.php

@@ -160,6 +160,7 @@ function wp_check_php_mysql_versions() {
  * Instead, send the headers for a zero-length favicon and bail.
  *
  * @since 3.0.0
+ * @deprecated 5.4.0 Deprecated in favor of do_favicon().
  */
 function wp_favicon_request() {
 	if ( '/favicon.ico' == $_SERVER['REQUEST_URI'] ) {

src/wp-includes/query.php

@@ -623,7 +623,7 @@ function is_preview() {
 }
 
 /**
- * Is the query for the robots file?
+ * Is the query for the robots.txt file?
  *
  * @since 2.1.0
  *
@@ -642,6 +642,26 @@ function is_robots() {
 	return $wp_query->is_robots();
 }
 
+/**
+ * Is the query for the favicon.ico file?
+ *
+ * @since 5.4.0
+ *
+ * @global WP_Query $wp_query WordPress Query object.
+ *
+ * @return bool
+ */
+function is_favicon() {
+	global $wp_query;
+
+	if ( ! isset( $wp_query ) ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
+		return false;
+	}
+
+	return $wp_query->is_favicon();
+}
+
 /**
  * Determines whether the query is for a search.
  *

src/wp-includes/template-loader.php

@@ -36,6 +36,14 @@ if ( is_robots() ) {
 	 */
 	do_action( 'do_robots' );
 	return;
+} elseif ( is_favicon() ) {
+	/**
+	 * Fired when the template loader determines a favicon.ico request.
+	 *
+	 * @since 5.4.0
+	 */
+	do_action( 'do_favicon' );
+	return;
 } elseif ( is_feed() ) {
 	do_feed();
 	return;

src/wp-includes/version.php

@@ -20,7 +20,7 @@ $wp_version = '5.4-alpha-46582-src';
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 45805;
+$wp_db_version = 47018;
 
 /**
  * Holds the TinyMCE version

src/wp-settings.php

@@ -63,9 +63,6 @@ wp_unregister_GLOBALS();
 // Standardize $_SERVER variables across setups.
 wp_fix_server_vars();
 
-// Check if we have received a request due to missing favicon.ico
-wp_favicon_request();
-
 // Check if we're in maintenance mode.
 wp_maintenance();
 

tests/phpunit/includes/abstract-testcase.php

@@ -962,6 +962,7 @@ abstract class WP_UnitTestCase_Base extends PHPUnit_Framework_TestCase {
 			'is_posts_page',
 			'is_preview',
 			'is_robots',
+			'is_favicon',
 			'is_search',
 			'is_single',
 			'is_singular',

tests/phpunit/tests/query/vars.php

@@ -60,6 +60,7 @@ class Tests_Query_Vars extends WP_UnitTestCase {
 				'subpost_id',
 				'preview',
 				'robots',
+				'favicon',
 				'taxonomy',
 				'term',
 				'cpage',