Media: Disable attachment pages for new installations.

WordPress creates attachment pages by default for every attachment uploaded. On the vast majority of sites, these attachment pages don't contain any meaningful information. They do however exist, get indexed by search engines, and sometimes even rank in search results, leading to bad results for users and site owners.

This commit introduces a `wp_attachment_pages_enabled` database option to control the attachment pages behavior:

* On existing sites, the option is set to `1` on upgrade, so that attachment pages continue to work as is.
* For new sites, the option is set to to `0` by default, which means attachment pages are redirected to the attachment URL.
* Sites that want to enable or disable the attachment pages can set the option to `1` or `0`, respectively.

Follow-up to [2958], [3303], [7149], [34690].

Props aristath, poena, afercia, joostdevalk, jonoaldersonwp, azaozz, johnbillion, joedolson, basiliskan, audrasjb, davelo, rilwis, manfcarlo, tyxla, garrett-eclipse, seedsca, eatingrules, matveb, antpb, zodiac1978, oglekler, zunaid321, costdev, SergeyBiryukov.
Fixes #57913.
Built from https://develop.svn.wordpress.org/trunk@56657


git-svn-id: http://core.svn.wordpress.org/trunk@56169 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/schema.php

@@ -556,6 +556,9 @@ function populate_options( array $options = array() ) {
 
 		// 5.8.0
 		'wp_force_deactivated_plugins'    => array(),
+
+		// 6.4.0
+		'wp_attachment_pages_enabled'     => 0,
 	);
 
 	// 3.3.0

wp-admin/includes/upgrade.php

@@ -839,6 +839,10 @@ function upgrade_all() {
 		upgrade_630();
 	}
 
+	if ( $wp_current_db_version < 56657 ) {
+		upgrade_640();
+	}
+
 	maybe_disable_link_manager();
 
 	maybe_disable_automattic_widgets();
@@ -2322,6 +2326,23 @@ function upgrade_630() {
 	}
 }
 
+/**
+ * Executes changes made in WordPress 6.4.0.
+ *
+ * @ignore
+ * @since 6.4.0
+ *
+ * @global int $wp_current_db_version The old (current) database version.
+ */
+function upgrade_640() {
+	global $wp_current_db_version;
+
+	if ( $wp_current_db_version < 56657 ) {
+		// Enable attachment pages.
+		update_option( 'wp_media_use_attachment_pages', 1 );
+	}
+}
+
 /**
  * Executes network-level upgrade routines.
  *

wp-includes/canonical.php

@@ -545,6 +545,18 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 		}
 	}
 
+	$is_attachment_redirect = false;
+
+	if ( is_attachment() && ! get_option( 'wp_attachment_pages_enabled' ) ) {
+		$attachment_id = get_query_var( 'attachment_id' );
+
+		if ( current_user_can( 'read_post', $attachment_id ) ) {
+			$redirect_url = wp_get_attachment_url( $attachment_id );
+
+			$is_attachment_redirect = true;
+		}
+	}
+
 	$redirect['query'] = preg_replace( '#^\??&*?#', '', $redirect['query'] );
 
 	// Tack on any additional query vars.
@@ -650,6 +662,7 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 
 	// Trailing slashes.
 	if ( is_object( $wp_rewrite ) && $wp_rewrite->using_permalinks()
+		&& ! $is_attachment_redirect
 		&& ! is_404() && ( ! is_front_page() || is_front_page() && get_query_var( 'paged' ) > 1 )
 	) {
 		$user_ts_type = '';

wp-includes/version.php

@@ -16,14 +16,14 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56656';
+$wp_version = '6.4-alpha-56657';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 55853;
+$wp_db_version = 56657;
 
 /**
  * Holds the TinyMCE version.