Improve error output for exception messages with special characters

examples/index.php

@@ -191,6 +191,7 @@
 $app->get('/error/yield', function () {
     yield null;
 });
+$app->get('/error/class', 'Acme\Http\UnknownDeleteUserController');
 
 // OPTIONS *
 $app->options('', function () {

src/HtmlHandler.php

@@ -24,7 +24,7 @@ public function statusResponse(int $statusCode, string $title, string $subtitle,
 h1 { margin: 0 .5em 0 0; border-right: calc(2 * max(0px, min(100vw - 700px + 1px, 1px))) solid #e3e4e7; padding-right: .5em; color: #aebdcc; font-size: 3em; }
 strong { color: #111827; font-size: 3em; }
 p { margin: .5em 0 0 0; grid-column: 2; color: #6b7280; }
-code { padding: 0 .3em; background-color: #f5f6f9; }
+code { padding: 0 .3em; background-color: #f5f6f9; } code span { padding: 0 .2em; border-radius: 3px; background-color: #0001; }
 a { color: inherit; }
 </style>
 </head>
@@ -50,13 +50,16 @@ public function statusResponse(int $statusCode, string $title, string $subtitle,
 
     public function escape(string $s): string
     {
-        return \addcslashes(
+        return \preg_replace_callback(
+            '/[\x00-\x1F]+/',
+            function (array $match): string {
+                return '<span>' . \addcslashes($match[0], "\x00..\xff") . '</span>';
+            },
             \preg_replace(
                 '/(^| ) |(?: $)/',
                 '$1&nbsp;',
                 \htmlspecialchars($s, \ENT_NOQUOTES | \ENT_SUBSTITUTE | \ENT_DISALLOWED, 'utf-8')
-            ),
-            "\0..\032\\"
+            )
         );
     }
 }

tests/AppTest.php

@@ -1329,27 +1329,27 @@ public function provideInvalidClasses()
     {
         yield [
             InvalidConstructorPrivate::class,
-            'Cannot instantiate class ' . addslashes(InvalidConstructorPrivate::class)
+            'Cannot instantiate class ' . InvalidConstructorPrivate::class
         ];
 
         yield [
             InvalidConstructorProtected::class,
-            'Cannot instantiate class ' . addslashes(InvalidConstructorProtected::class)
+            'Cannot instantiate class ' . InvalidConstructorProtected::class
         ];
 
         yield [
             InvalidAbstract::class,
-            'Cannot instantiate abstract class ' . addslashes(InvalidAbstract::class)
+            'Cannot instantiate abstract class ' . InvalidAbstract::class
         ];
 
         yield [
             InvalidInterface::class,
-            'Cannot instantiate interface ' . addslashes(InvalidInterface::class)
+            'Cannot instantiate interface ' . InvalidInterface::class
         ];
 
         yield [
             InvalidTrait::class,
-            'Cannot instantiate trait ' . addslashes(InvalidTrait::class)
+            'Cannot instantiate trait ' . InvalidTrait::class
         ];
 
         yield [
@@ -1413,7 +1413,7 @@ public function testHandleRequestWithMatchingRouteReturnsInternalServerErrorResp
 
         $this->assertStringContainsString("<title>Error 500: Internal Server Error</title>\n", (string) $response->getBody());
         $this->assertStringContainsString("<p>The requested page failed to load, please try again later.</p>\n", (string) $response->getBody());
-        $this->assertStringMatchesFormat("%a<p>Expected request handler to return <code>Psr\Http\Message\ResponseInterface</code> but got uncaught <code>BadMethodCallException</code> with message <code>Request handler class " . addslashes($class) . " failed to load: $error</code> in <code title=\"See %s\">Container.php:%d</code>.</p>\n%a", (string) $response->getBody());
+        $this->assertStringMatchesFormat("%a<p>Expected request handler to return <code>Psr\Http\Message\ResponseInterface</code> but got uncaught <code>BadMethodCallException</code> with message <code>Request handler class " . $class . " failed to load: $error</code> in <code title=\"See %s\">Container.php:%d</code>.</p>\n%a", (string) $response->getBody());
     }
 
     public function testHandleRequestWithMatchingRouteReturnsInternalServerErrorResponseWhenHandlerClassRequiresUnexpectedCallableParameter()

tests/ErrorHandlerTest.php

@@ -407,15 +407,15 @@ public function provideExceptionMessage()
             ],
             [
                 "new\n line",
-                'new\n line'
+                'new<span>\n</span> line'
             ],
             [
                 'sla/she\'s\\n',
-                'sla/she\'s\\\\n'
+                'sla/she\'s\\n'
             ],
             [
                 "hello\r\nworld",
-                'hello\r\nworld'
+                'hello<span>\r\n</span>world'
             ],
             [
                 '"with"<html>',

tests/HtmlHandlerTest.php

@@ -44,15 +44,15 @@ public function provideNames()
             ],
             [
                 "hello\nworld",
-                'hello\nworld'
+                'hello<span>\n</span>world'
             ],
             [
                 "hello\tworld",
-                'hello\tworld'
+                'hello<span>\t</span>world'
             ],
             [
                 "hello\\nworld",
-                'hello\\\\nworld'
+                'hello\nworld'
             ],
             [
                 'h<e>llo',