Issue #1915752 by dawehner, tim.plunkett: routes are not found when 0 is used as a placeholder value.

core/includes/common.inc

@@ -5099,7 +5099,9 @@ function drupal_set_page_content($content = NULL) {
   $content_block = &drupal_static(__FUNCTION__, NULL);
   $main_content_display = &drupal_static('system_main_content_added', FALSE);
 
-  if (!empty($content)) {
+  // Filter out each empty value, though allow '0' and 0, which would be
+  // filtered out by empty().
+  if ($content !== NULL && $content !== '') {
     $content_block = (is_array($content) ? $content : array('main' => array('#markup' => $content)));
   }
   else {

core/lib/Drupal/Core/Routing/RouteProvider.php

@@ -97,7 +97,11 @@ class RouteProvider implements RouteProviderInterface {
       $path = rtrim($request->getPathInfo(), '/');
     }
 
-    $parts = array_slice(array_filter(explode('/', $path)), 0, MatcherDumper::MAX_PARTS);
+    // Filter out each empty value, though allow '0' and 0, which would be
+    // filtered out by empty().
+    $parts = array_slice(array_filter(explode('/', $path), function($value) {
+      return $value !== NULL && $value !== '';
+    }), 0, MatcherDumper::MAX_PARTS);
 
     $ancestors = $this->getCandidateOutlines($parts);
 

core/modules/system/lib/Drupal/system/Tests/Routing/RouteProviderTest.php

@@ -271,6 +271,41 @@ class RouteProviderTest extends UnitTestBase {
     }
   }
 
+  /**
+   * Tests a route with a 0 as value.
+   */
+  public function testOutlinePathMatchZero() {
+    $connection = Database::getConnection();
+    $provider = new RouteProvider($connection, 'test_routes');
+
+    $this->fixtures->createTables($connection);
+
+    $collection = new RouteCollection();
+    $collection->add('poink', new Route('/some/path/{value}'));
+
+    $dumper = new MatcherDumper($connection, 'test_routes');
+    $dumper->addRoutes($collection);
+    $dumper->dump();
+
+    $path = '/some/path/0';
+
+    $request = Request::create($path, 'GET');
+
+    try {
+      $routes = $provider->getRouteCollectionForRequest($request);
+
+      // All of the matching paths have the correct pattern.
+      foreach ($routes as $route) {
+        $this->assertEqual($route->compile()->getPatternOutline(), '/some/path/%', 'Found path has correct pattern');
+      }
+
+      $this->assertEqual(count($routes), 1, 'The correct number of routes was found.');
+    }
+    catch (ResourceNotFoundException $e) {
+      $this->fail('No matchout route found with 0 as argument value');
+    }
+  }
+
   /**
    * Confirms that an exception is thrown when no matching path is found.
    */

core/modules/system/lib/Drupal/system/Tests/Routing/RouterTest.php

@@ -57,9 +57,13 @@ class RouterTest extends WebTestBase {
    * Confirms that placeholders in paths work correctly.
    */
   public function testControllerPlaceholders() {
-    $value = $this->randomName();
-    $this->drupalGet('router_test/test3/' . $value);
-    $this->assertRaw($value, 'The correct string was returned because the route was successful.');
+    // Test with 0 and a random value.
+    $values = array("0", $this->randomName());
+    foreach ($values as $value) {
+      $this->drupalGet('router_test/test3/' . $value);
+      $this->assertResponse(200);
+      $this->assertRaw($value, 'The correct string was returned because the route was successful.');
+    }
 
     // Confirm that the page wrapping is being added, so we're not getting a
     // raw body returned.