[10.x] Handle relative ASSET_URL (#43900)

Author: iamgergo

src/Illuminate/Routing/UrlGenerator.php

@@ -255,7 +255,7 @@ public function asset($path, $secure = null)
         // for asset paths, but only for routes to endpoints in the application.
         $root = $this->assetRoot ?: $this->formatRoot($this->formatScheme($secure));
 
-        return $this->removeIndex($root).'/'.trim($path, '/');
+        return Str::finish($this->removeIndex($root), '/').trim($path, '/');
     }
 
     /**

tests/Routing/RoutingUrlGeneratorTest.php

@@ -41,17 +41,26 @@ public function testBasicGeneration()
         );
 
         $this->assertSame('https://www.foo.com/foo/bar', $url->to('foo/bar'));
+    }
 
-        /*
-         * Test asset URL generation...
-         */
+    public function testAssetGeneration()
+    {
         $url = new UrlGenerator(
             new RouteCollection,
             Request::create('http://www.foo.com/index.php/')
         );
 
         $this->assertSame('http://www.foo.com/foo/bar', $url->asset('foo/bar'));
         $this->assertSame('https://www.foo.com/foo/bar', $url->asset('foo/bar', true));
+
+        $url = new UrlGenerator(
+            new RouteCollection,
+            Request::create('http://www.foo.com/index.php/'),
+            '/'
+        );
+
+        $this->assertSame('/foo/bar', $url->asset('foo/bar'));
+        $this->assertSame('/foo/bar', $url->asset('foo/bar', true));
     }
 
     public function testBasicGenerationWithHostFormatting()