Prevent deprecation notice based on triggering error middleware

Users cannot yet set the raiseThrowables flag, as there are not shipped
facilities for handling errors using templates or whoops. As such,
currently, if the queue is exhausted or an exception is thrown, error
middleware is triggered. This patch adds an error handler to
`Application::__invoke()` to swallow deprecation notices due to
invocation of error middleware.

src/Application.php

@@ -130,21 +130,31 @@ public function __construct(
      * If $out is not provided, uses the result of `getFinalHandler()`.
      *
      * @todo Remove logic for creating final handler for version 2.0.
+     * @todo Remove error handler for deprecation notice due to triggering
+     *     error middleware for version 2.0.0.
      * @param ServerRequestInterface $request
      * @param ResponseInterface $response
      * @param callable|null $out
      * @return ResponseInterface
      */
     public function __invoke(ServerRequestInterface $request, ResponseInterface $response, callable $out = null)
     {
+        set_error_handler(function ($errno, $errstr) {
+            return false !== strstr($errstr, 'error middleware is deprecated');
+        }, E_USER_DEPRECATED);
+
         if (! $out && (null === ($out = $this->getFinalHandler($response)))) {
             $response = $response instanceof StratigilityResponse
                 ? $response
                 : new StratigilityResponse($response);
             $out = new FinalHandler([], $response);
         }
 
-        return parent::__invoke($request, $response, $out);
+        $result = parent::__invoke($request, $response, $out);
+
+        restore_error_handler();
+
+        return $result;
     }
 
     /**

test/Container/ApplicationFactoryIntegrationTest.php

@@ -128,14 +128,8 @@ public function testConfiguredErrorMiddlewarePipeIsExecutedWhenMiddlewareCallsNe
         $request = new ServerRequest([], [], 'http://example.com/needs/authentication', 'GET');
         $response = new Response();
 
-        set_error_handler(function ($errno, $errstr) {
-            return false !== strstr($errstr, 'error middleware is deprecated');
-        }, E_USER_DEPRECATED);
-
         $response = $app($request, $response);
 
-        restore_error_handler();
-
         $this->assertInstanceOf(ResponseInterface::class, $response);
         $this->assertEquals(401, $response->getStatusCode(), 'Unexpected response');
         $this->assertTrue($response->hasHeader('X-Always'));
@@ -222,14 +216,8 @@ public function testConfiguredErrorMiddlewareIsExecutedWhenMiddlewareCallsNextWi
         $request = new ServerRequest([], [], 'http://example.com/needs/authentication', 'GET');
         $response = new Response();
 
-        set_error_handler(function ($errno, $errstr) {
-            return false !== strstr($errstr, 'error middleware is deprecated');
-        }, E_USER_DEPRECATED);
-
         $response = $app($request, $response);
 
-        restore_error_handler();
-
         $this->assertInstanceOf(ResponseInterface::class, $response);
         $this->assertEquals(401, $response->getStatusCode(), 'Unexpected response');
         $this->assertTrue($response->hasHeader('X-Always'));