mu-plugin: Redirect old content to the new URL structure.

source/wp-content/mu-plugins/site-documentation.php

@@ -10,6 +10,7 @@
 namespace WordPressdotorg\Documentation_2022\MU_Plugin;
 
 add_action( 'template_redirect', __NAMESPACE__ . '\redirect_to_google_search' );
+add_action( 'template_redirect', __NAMESPACE__ . '\redirect_old_content', 9 ); // Before redirect_canonical();
 
 /**
  * Redirects search results to Google Custom Search.
@@ -26,3 +27,49 @@ function redirect_to_google_search() {
 		exit;
 	}
 }
+
+/**
+ * Redirects old content to the new URL structure.
+ *
+ * This does not include the article renaming since core will handle that.
+ */
+function redirect_old_content() {
+	$path_redirects = [
+		// Removed articles.
+		'/documentation/article/wordpress-features/' => 'https://wordpress.org/about/features/',
+		'/documentation/article/requirements/'       => 'https://wordpress.org/about/requirements/',
+
+		// Renamed categories.
+		'/documentation/category/basic-administration/' => '/documentation/category/dashboard/',
+		'/documentation/category/troubleshooting/'      => '/documentation/category/faqs/',
+		'/documentation/category/installation/'         => '/documentation/category/installation/',
+		'/documentation/category/maintenance/'          => '/documentation/category/maintenance/',
+		'/documentation/category/security/'             => '/documentation/category/security/',
+		'/documentation/category/getting-started/'      => '/documentation/category/where-to-start/',
+
+		// Top-level category landing pages.
+		'/documentation/category/customizing/' => '/documentation/customization/',
+		'/documentation/category/basic-usage/' => '/documentation/support-guides/',
+
+		// @todo When the Advanced Administration handbook is updated, add those redirects here.
+	];
+
+	$request_uri = $_SERVER['REQUEST_URI'] ?? '/documentation-test/'; // phpcs:ignore
+
+	foreach ( $path_redirects as $old_path => $new_url ) {
+		if ( str_starts_with( $request_uri, $old_path ) ) {
+			do_redirect_and_exit( $new_url );
+		}
+	}
+}
+
+/**
+ * Do the 301 redirect and exit the script.
+ */
+function do_redirect_and_exit( $location ) {
+	header_remove( 'expires' );
+	header_remove( 'cache-control' );
+
+	wp_safe_redirect( $location, 301 );
+	exit;
+}