fix(router): match StaticRouter root route on the page root

src/Http/Request/InteractsWithHeaders.php

@@ -19,7 +19,7 @@ trait InteractsWithHeaders
      *
      * @return array<string, string>
      */
-    public function headers()
+    public function headers(): array
     {
         return array_map('sanitize_text_field', $this->rawHeaders());
     }
@@ -51,7 +51,7 @@ public function rawHeader(string $name, ?string $default = null)
      *
      * @return bool
      */
-    public function hasHeader(string $name)
+    public function hasHeader(string $name): bool
     {
         return \array_key_exists(self::canonicalHeaderName($name), $this->rawHeaders());
     }
@@ -64,7 +64,7 @@ public function hasHeader(string $name)
     private function rawHeaders(): array
     {
         if (isset($this->rest) && $this->rest instanceof WP_REST_Request) {
-            return array_map(static fn ($values) => implode(', ', (array) $values), (array) $this->rest->get_headers());
+            return array_map(static fn ($values): string => implode(', ', (array) $values), (array) $this->rest->get_headers());
         }
 
         return $this->serverHeaders();

src/Http/Router/RouteRegister.php

@@ -526,7 +526,7 @@ private function invokeAsReflectionFunction(callable $method): mixed
         return $reflectionFunction->invoke(...$params);
     }
 
-    private function processParameters($reflectionParams, array $params = []): array
+    private function processParameters(array $reflectionParams, array $params = []): array
     {
         $requestParams = [];
         foreach ($reflectionParams as $param) {

src/Http/Router/StaticRouter.php

@@ -215,12 +215,20 @@ private function routePath(RouteRegister $route): string
         $prefix = trim((string) $route->getRoutePrefix(), '/');
         $path   = trim((string) $route->getPath(), '/');
 
-        return $prefix === '' ? $path : $prefix . '/' . $path;
+        return self::joinPath($prefix, $path);
+    }
+
+    /**
+     * Joins path segments with '/', skipping empty ones so a root route leaves no trailing slash.
+     */
+    private static function joinPath(string ...$segments): string
+    {
+        return implode('/', array_filter($segments, static fn (string $segment): bool => $segment !== ''));
     }
 
     private function isRouteMatched(RouteRegister $route, string $requestPath): bool
     {
-        $path     = $this->pageName . '/' . $this->routePath($route);
+        $path     = self::joinPath($this->pageName, $this->routePath($route));
         $compiled = RoutePattern::compile($path);
         $pattern  = $compiled === null ? preg_quote($path, '~') : $compiled['regex'];
 

tests/Router/StaticRoutingTest.php

@@ -558,13 +558,109 @@ public function testRootRuleCoexistsWithOtherRoutes(): void
         assertTest(isset(WpKitTestState::$rewriteRules['^landing/entries/([^/]+)/?$']), 'route rule missing next to the root rule');
     }
 
-    private function makeTransport(array $routes = []): StaticRouter
+    public function testRootRouteMatchesTheParsedPageRoot(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        $this->setParsedRequest('landing');
+
+        do_action('template_redirect');
+
+        assertSameValue('page-home', apply_filters('the_content', 'page-'), 'root route did not match the parsed page root');
+    }
+
+    public function testRootRouteMatchesThePageRootOnSubdirectoryInstalls(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        WpKitTestState::$options['home'] = 'https://example.test/blog';
+        $_SERVER['REQUEST_URI']          = '/blog/landing';
+
+        do_action('template_redirect');
+
+        assertSameValue('page-home', apply_filters('the_content', 'page-'), 'root route did not match on a subdirectory install');
+    }
+
+    public function testRootRouteMatchesThePageRootFromTheRequestUri(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        $_SERVER['REQUEST_URI'] = '/landing';
+
+        do_action('template_redirect');
+
+        assertSameValue('page-home', apply_filters('the_content', 'page-'), 'root route did not match a page root without a trailing slash');
+    }
+
+    public function testRootRouteMatchesThePageRootFromATrailingSlashRequestUri(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        $_SERVER['REQUEST_URI'] = '/landing/?preview=1';
+
+        do_action('template_redirect');
+
+        assertSameValue('page-home', apply_filters('the_content', 'page-'), 'root route did not match a page root with a trailing slash');
+    }
+
+    public function testRootRouteDoesNotMatchDeeperPaths(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        $this->setParsedRequest('landing/entries/42');
+
+        do_action('template_redirect');
+
+        assertTest(!isset(WpKitTestState::$filters['the_content']), 'root route matched a deeper path');
+    }
+
+    public function testRootRouteDoesNotMatchAPageSharingItsNamePrefix(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'home']);
+        $this->setParsedRequest('landing-archive');
+
+        do_action('template_redirect');
+
+        assertTest(!isset(WpKitTestState::$filters['the_content']), 'root route matched another page sharing its name prefix');
+    }
+
+    public function testRootRouteDoesNotShadowSiblingRoutes(): void
+    {
+        $this->makeTransport([
+            '/'         => static fn () => 'home',
+            'user/{id}' => static fn ($id) => 'user ' . $id,
+        ]);
+        $this->setParsedRequest('landing/user/5');
+
+        do_action('template_redirect');
+
+        assertSameValue('page-user 5', apply_filters('the_content', 'page-'), 'root route shadowed a sibling route');
+    }
+
+    public function testEmptyPathInsideAPrefixMatchesThePrefixRoot(): void
+    {
+        $this->makeTransport(['/' => static fn () => 'account'], 'account');
+        $this->setParsedRequest('landing/account');
+
+        do_action('template_redirect');
+
+        assertSameValue('page-account', apply_filters('the_content', 'page-'), 'empty path inside a prefix did not match the prefix root');
+    }
+
+    /**
+     * Registers the given GET routes, optionally under a prefix, on a static router for the landing page.
+     */
+    private function makeTransport(array $routes = [], ?string $prefix = null): StaticRouter
     {
         new Router('static', 'landing', null);
         foreach ($routes as $path => $action) {
-            (new RouteBase())->get($path, $action);
+            (new RouteBase())->prefix($prefix)->get($path, $action);
         }
 
         return new StaticRouter('landing', 'plugin_activate', 'plugin_deactivate');
     }
+
+    /**
+     * Sets the parsed WP request path that the router reads from the global WP object.
+     */
+    private function setParsedRequest(string $path): void
+    {
+        $GLOBALS['wp']          = new \WP();
+        $GLOBALS['wp']->request = $path;
+    }
 }