Merge branch '3.4' into 4.4

* 3.4:
  [Filesystem] Handle paths on different drives
  [WebProfiler] Do not add src-elem CSP directives if they do not exist
  [Yaml] fix parse error when unindented collections contain a comment
  [3.4][Inflector] Improve testSingularize() argument name
  [PhpUnitBridge] fix PHP 5.3 compat again
  Skip validation when email is an empty object
  fix sr_Latn translation
  [Validator] fix lazy property usage.
  Fix annotation
  [PhpUnitBridge] fix compat with PHP 5.3
  [DX] Show the ParseException message in YAML file loaders

Author: nicolas-grekas

Csp/ContentSecurityPolicyHandler.php

@@ -129,12 +129,11 @@ private function updateCspHeaders(Response $response, array $nonces = []): array
                     continue;
                 }
                 if (!isset($headers[$header][$type])) {
-                    if (isset($headers[$header]['default-src'])) {
-                        $headers[$header][$type] = $headers[$header]['default-src'];
-                    } else {
-                        // If there is no script-src/style-src and no default-src, no additional rules required.
+                    if (null === $fallback = $this->getDirectiveFallback($directives, $type)) {
                         continue;
                     }
+
+                    $headers[$header][$type] = $fallback;
                 }
                 $ruleIsSet = true;
                 if (!\in_array('\'unsafe-inline\'', $headers[$header][$type], true)) {
@@ -199,9 +198,7 @@ private function authorizesInline(array $directivesSet, string $type): bool
     {
         if (isset($directivesSet[$type])) {
             $directives = $directivesSet[$type];
-        } elseif (isset($directivesSet['default-src'])) {
-            $directives = $directivesSet['default-src'];
-        } else {
+        } elseif (null === $directives = $this->getDirectiveFallback($directivesSet, $type)) {
             return false;
         }
 
@@ -225,6 +222,16 @@ private function hasHashOrNonce(array $directives): bool
         return false;
     }
 
+    private function getDirectiveFallback(array $directiveSet, $type)
+    {
+        if (\in_array($type, ['script-src-elem', 'style-src-elem'], true) || !isset($directiveSet['default-src'])) {
+            // Let the browser fallback on it's own
+            return null;
+        }
+
+        return $directiveSet['default-src'];
+    }
+
     /**
      * Retrieves the Content-Security-Policy headers (either X-Content-Security-Policy or Content-Security-Policy) from
      * a response.

Tests/Csp/ContentSecurityPolicyHandlerTest.php

@@ -131,7 +131,14 @@ public function provideRequestAndResponsesForOnKernelResponse()
                 ['csp_script_nonce' => $nonce, 'csp_style_nonce' => $nonce],
                 $this->createRequest(),
                 $this->createResponse(['Content-Security-Policy' => 'default-src \'self\' domain.com; script-src \'self\' \'unsafe-inline\'', 'Content-Security-Policy-Report-Only' => 'default-src \'self\' domain-report-only.com; script-src \'self\' \'unsafe-inline\'']),
-                ['Content-Security-Policy' => 'default-src \'self\' domain.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\' domain.com \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src \'self\' domain.com \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src-elem \'self\' domain.com \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'Content-Security-Policy-Report-Only' => 'default-src \'self\' domain-report-only.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\' domain-report-only.com \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src \'self\' domain-report-only.com \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src-elem \'self\' domain-report-only.com \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'X-Content-Security-Policy' => null],
+                ['Content-Security-Policy' => 'default-src \'self\' domain.com; script-src \'self\' \'unsafe-inline\'; style-src \'self\' domain.com \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'Content-Security-Policy-Report-Only' => 'default-src \'self\' domain-report-only.com; script-src \'self\' \'unsafe-inline\'; style-src \'self\' domain-report-only.com \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'X-Content-Security-Policy' => null],
+            ],
+            [
+                $nonce,
+                ['csp_script_nonce' => $nonce, 'csp_style_nonce' => $nonce],
+                $this->createRequest(),
+                $this->createResponse(['Content-Security-Policy' => 'default-src \'self\' domain.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\'; style-src \'self\' \'unsafe-inline\'; style-src-elem \'self\'', 'Content-Security-Policy-Report-Only' => 'default-src \'self\' domain-report-only.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\'; style-src \'self\' \'unsafe-inline\'; style-src-elem \'self\'']),
+                ['Content-Security-Policy' => 'default-src \'self\' domain.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\' \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src \'self\' \'unsafe-inline\'; style-src-elem \'self\' \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'Content-Security-Policy-Report-Only' => 'default-src \'self\' domain-report-only.com; script-src \'self\' \'unsafe-inline\'; script-src-elem \'self\' \'unsafe-inline\' \'nonce-'.$nonce.'\'; style-src \'self\' \'unsafe-inline\'; style-src-elem \'self\' \'unsafe-inline\' \'nonce-'.$nonce.'\'', 'X-Content-Security-Policy' => null],
             ],
             [
                 $nonce,