去除 WordPress 分類網址的 /category/：3 種做法與注意事項

RewriteEngine On
RewriteRule ^category/(.*)$ /topics/$1 [R=301,L]

/**
 * 去除 WordPress 分類網址中的 /category/
 */

// 1) 產生分類連結時不加前綴
add_action( 'init', function () {
    global $wp_rewrite;
    if ( isset( $wp_rewrite->extra_permastructs['category'] ) ) {
        $wp_rewrite->extra_permastructs['category']['struct'] = '%category%';
    }
} );

// 2) 為每個分類建立網址規則,並接住舊的 /category/ 網址
add_filter( 'category_rewrite_rules', function () {
    $rules = array();

    foreach ( get_categories( array( 'hide_empty' => false ) ) as $category ) {
        $path = $category->slug;
        if ( $category->parent ) {
            $parents = get_category_parents( $category->parent, false, '/', true );
            if ( ! is_wp_error( $parents ) ) {
                $path = $parents . $path;
            }
        }
        $path = urldecode( $path ); // 讓中文代稱也能對應

        $rules[ '(' . $path . ')/(?:feed/)?(feed|rdf|rss|rss2|atom)/?$' ] = 'index.php?category_name=$matches[1]&feed=$matches[2]';
        $rules[ '(' . $path . ')/page/?([0-9]{1,})/?$' ]                  = 'index.php?category_name=$matches[1]&paged=$matches[2]';
        $rules[ '(' . $path . ')/?$' ]                                    = 'index.php?category_name=$matches[1]';
    }

    $old_base = trim( get_option( 'category_base' ) ?: 'category', '/' );
    $rules[ $old_base . '/(.*)$' ] = 'index.php?ahwei_old_category=$matches[1]';

    return $rules;
} );

// 3) 舊網址 301 轉到新網址
add_filter( 'query_vars', function ( $vars ) {
    $vars[] = 'ahwei_old_category';
    return $vars;
} );

add_filter( 'request', function ( $query_vars ) {
    if ( isset( $query_vars['ahwei_old_category'] ) ) {
        $path = trim( $query_vars['ahwei_old_category'], '/' );
        wp_safe_redirect( home_url( user_trailingslashit( $path, 'category' ) ), 301 );
        exit;
    }
    return $query_vars;
} );

// 4) 新增、修改、刪除分類時,自動更新網址規則
foreach ( array( 'created_category', 'edited_category', 'delete_category' ) as $hook ) {
    add_action( $hook, function () {
        flush_rewrite_rules( false );
    } );
}