diff --git a/.travis.yml b/.travis.yml
index 1fc3647f66..61d060433e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -28,7 +28,11 @@ matrix:
           env: deps=high
         - php: 7.4
           env: deps=low
+        - php: nightly
+          services: [memcached]
     fast_finish: true
+    allow_failures:
+      - php: nightly
 
 cache:
     directories:
@@ -135,7 +139,9 @@ before_install:
           echo session.gc_probability = 0 >> $INI
           echo opcache.enable_cli = 1 >> $INI
           echo apc.enable_cli = 1 >> $INI
-          echo extension = memcached.so >> $INI
+          if [[ $PHP != nightly ]]; then
+              echo extension = memcached.so >> $INI
+          fi
       done
 
     - |
@@ -147,6 +153,9 @@ before_install:
           if ! php --ri sodium > /dev/null; then
               tfold ext.libsodium tpecl libsodium sodium.so $INI
           fi
+          if [[ $PHP = nightly ]]; then
+              tfold ext.memcached tpecl memcached-3.1.5 memcached.so $INI
+          fi
 
           tfold ext.apcu tpecl apcu-5.1.17 apcu.so $INI
           tfold ext.mongodb tpecl mongodb-1.6.0 mongodb.so $INI
@@ -223,6 +232,12 @@ install:
           export COMPONENTS=$(find src/Symfony -mindepth 3 -type f -name phpunit.xml.dist -not -wholename '*/Bridge/PhpUnit/*' -printf '%h\n' | sort)
       fi
 
+    - |
+      # Set composer's platform to php 7.4 if we're on php 8.
+      if [[ $PHP = nightly ]]; then
+          composer config platform.php 7.4.99
+      fi
+
     - |
       # Install symfony/flex
       if [[ $deps = low ]]; then
diff --git a/src/Symfony/Component/Cache/Tests/Adapter/MemcachedAdapterTest.php b/src/Symfony/Component/Cache/Tests/Adapter/MemcachedAdapterTest.php
index 988ff22051..4aaba13425 100644
--- a/src/Symfony/Component/Cache/Tests/Adapter/MemcachedAdapterTest.php
+++ b/src/Symfony/Component/Cache/Tests/Adapter/MemcachedAdapterTest.php
@@ -71,8 +71,14 @@ class MemcachedAdapterTest extends AdapterTestCase
      */
     public function testBadOptions($name, $value)
     {
-        $this->expectException('ErrorException');
-        $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
+        if (\PHP_VERSION_ID < 80000) {
+            $this->expectException('ErrorException');
+            $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
+        } else {
+            $this->expectException('Error');
+            $this->expectExceptionMessage('Undefined class constant \'Memcached::');
+        }
+
         MemcachedAdapter::createConnection([], [$name => $value]);
     }
 
diff --git a/src/Symfony/Component/Cache/Tests/Simple/MemcachedCacheTest.php b/src/Symfony/Component/Cache/Tests/Simple/MemcachedCacheTest.php
index 2209c955f0..90641911e9 100644
--- a/src/Symfony/Component/Cache/Tests/Simple/MemcachedCacheTest.php
+++ b/src/Symfony/Component/Cache/Tests/Simple/MemcachedCacheTest.php
@@ -81,8 +81,14 @@ class MemcachedCacheTest extends CacheTestCase
      */
     public function testBadOptions(string $name, $value)
     {
-        $this->expectException('ErrorException');
-        $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
+        if (\PHP_VERSION_ID < 80000) {
+            $this->expectException('ErrorException');
+            $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
+        } else {
+            $this->expectException('Error');
+            $this->expectExceptionMessage('Undefined class constant \'Memcached::');
+        }
+
         MemcachedCache::createConnection([], [$name => $value]);
     }
 
diff --git a/src/Symfony/Component/VarDumper/Caster/Caster.php b/src/Symfony/Component/VarDumper/Caster/Caster.php
index 81e238c321..4bdc66ac5b 100644
--- a/src/Symfony/Component/VarDumper/Caster/Caster.php
+++ b/src/Symfony/Component/VarDumper/Caster/Caster.php
@@ -45,7 +45,7 @@ class Caster
      *
      * @return array The array-cast of the object, with prefixed dynamic properties
      */
-    public static function castObject($obj, string $class, bool $hasDebugInfo = false): array
+    public static function castObject($obj, string $class, bool $hasDebugInfo = false, string $debugClass = null): array
     {
         if ($hasDebugInfo) {
             try {
@@ -64,6 +64,7 @@ class Caster
 
         if ($a) {
             static $publicProperties = [];
+            $debugClass = $debugClass ?? get_debug_type($obj);
 
             $i = 0;
             $prefixedKeys = [];
@@ -77,8 +78,8 @@ class Caster
                     if (!isset($publicProperties[$class][$k])) {
                         $prefixedKeys[$i] = self::PREFIX_DYNAMIC.$k;
                     }
-                } elseif (isset($k[16]) && "\0" === $k[16] && 0 === strpos($k, "\0class@anonymous\0")) {
-                    $prefixedKeys[$i] = "\0".get_parent_class($class).'@anonymous'.strrchr($k, "\0");
+                } elseif ($debugClass !== $class && 1 === strpos($k, $class)) {
+                    $prefixedKeys[$i] = "\0".$debugClass.strrchr($k, "\0");
                 }
                 ++$i;
             }
@@ -94,6 +95,9 @@ class Caster
         if ($hasDebugInfo && \is_array($debugInfo)) {
             foreach ($debugInfo as $k => $v) {
                 if (!isset($k[0]) || "\0" !== $k[0]) {
+                    if (\array_key_exists(self::PREFIX_DYNAMIC.$k, $a)) {
+                        continue;
+                    }
                     $k = self::PREFIX_VIRTUAL.$k;
                 }
 
diff --git a/src/Symfony/Component/VarDumper/Caster/SplCaster.php b/src/Symfony/Component/VarDumper/Caster/SplCaster.php
index 0bb773e07b..5d2227d418 100644
--- a/src/Symfony/Component/VarDumper/Caster/SplCaster.php
+++ b/src/Symfony/Component/VarDumper/Caster/SplCaster.php
@@ -162,15 +162,6 @@ class SplCaster
         return $a;
     }
 
-    public static function castFixedArray(\SplFixedArray $c, array $a, Stub $stub, $isNested)
-    {
-        $a += [
-            Caster::PREFIX_VIRTUAL.'storage' => $c->toArray(),
-        ];
-
-        return $a;
-    }
-
     public static function castObjectStorage(\SplObjectStorage $c, array $a, Stub $stub, $isNested)
     {
         $storage = [];
@@ -209,14 +200,16 @@ class SplCaster
     private static function castSplArray($c, array $a, Stub $stub, bool $isNested): array
     {
         $prefix = Caster::PREFIX_VIRTUAL;
-        $class = $stub->class;
         $flags = $c->getFlags();
 
         if (!($flags & \ArrayObject::STD_PROP_LIST)) {
             $c->setFlags(\ArrayObject::STD_PROP_LIST);
-            $a = Caster::castObject($c, $class);
+            $a = Caster::castObject($c, \get_class($c), method_exists($c, '__debugInfo'), $stub->class);
             $c->setFlags($flags);
         }
+        if (\PHP_VERSION_ID < 70400) {
+            $a[$prefix.'storage'] = $c->getArrayCopy();
+        }
         $a += [
             $prefix.'flag::STD_PROP_LIST' => (bool) ($flags & \ArrayObject::STD_PROP_LIST),
             $prefix.'flag::ARRAY_AS_PROPS' => (bool) ($flags & \ArrayObject::ARRAY_AS_PROPS),
@@ -224,7 +217,6 @@ class SplCaster
         if ($c instanceof \ArrayObject) {
             $a[$prefix.'iteratorClass'] = new ClassStub($c->getIteratorClass());
         }
-        $a[$prefix.'storage'] = $c->getArrayCopy();
 
         return $a;
     }
diff --git a/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php b/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
index 4bf22aff97..6ecf366955 100644
--- a/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
+++ b/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
@@ -114,7 +114,6 @@ abstract class AbstractCloner implements ClonerInterface
         'SplDoublyLinkedList' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castDoublyLinkedList'],
         'SplFileInfo' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castFileInfo'],
         'SplFileObject' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castFileObject'],
-        'SplFixedArray' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castFixedArray'],
         'SplHeap' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castHeap'],
         'SplObjectStorage' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castObjectStorage'],
         'SplPriorityQueue' => ['Symfony\Component\VarDumper\Caster\SplCaster', 'castHeap'],
@@ -291,8 +290,8 @@ abstract class AbstractCloner implements ClonerInterface
         $obj = $stub->value;
         $class = $stub->class;
 
-        if (isset($class[15]) && "\0" === $class[15] && 0 === strpos($class, "class@anonymous\x00")) {
-            $stub->class = get_parent_class($class).'@anonymous';
+        if (\PHP_VERSION_ID < 80000 ? "\0" === ($class[15] ?? null) : false !== strpos($class, "@anonymous\0")) {
+            $stub->class = get_debug_type($obj);
         }
         if (isset($this->classInfo[$class])) {
             list($i, $parents, $hasDebugInfo, $fileInfo) = $this->classInfo[$class];
@@ -321,7 +320,7 @@ abstract class AbstractCloner implements ClonerInterface
         }
 
         $stub->attr += $fileInfo;
-        $a = Caster::castObject($obj, $class, $hasDebugInfo);
+        $a = Caster::castObject($obj, $class, $hasDebugInfo, $stub->class);
 
         try {
             while ($i--) {
diff --git a/src/Symfony/Component/VarDumper/Tests/Caster/CasterTest.php b/src/Symfony/Component/VarDumper/Tests/Caster/CasterTest.php
index 2c2189c8b5..a150475dc6 100644
--- a/src/Symfony/Component/VarDumper/Tests/Caster/CasterTest.php
+++ b/src/Symfony/Component/VarDumper/Tests/Caster/CasterTest.php
@@ -168,7 +168,7 @@ EOTXT
 
         $this->assertDumpMatchesFormat(
             <<<'EOTXT'
-@anonymous {
+class@anonymous {
   -foo: "foo"
 }
 EOTXT
diff --git a/src/Symfony/Component/VarDumper/Tests/Caster/PdoCasterTest.php b/src/Symfony/Component/VarDumper/Tests/Caster/PdoCasterTest.php
index 19bbe0f80c..fca242cfc6 100644
--- a/src/Symfony/Component/VarDumper/Tests/Caster/PdoCasterTest.php
+++ b/src/Symfony/Component/VarDumper/Tests/Caster/PdoCasterTest.php
@@ -30,6 +30,7 @@ class PdoCasterTest extends TestCase
     {
         $pdo = new \PDO('sqlite::memory:');
         $pdo->setAttribute(\PDO::ATTR_STATEMENT_CLASS, ['PDOStatement', [$pdo]]);
+        $pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
 
         $cast = PdoCaster::castPdo($pdo, [], new Stub(), false);
 
@@ -45,7 +46,7 @@ array:2 [
   "\x00~\x00inTransaction" => false
   "\x00~\x00attributes" => array:9 [
     "CASE" => NATURAL
-    "ERRMODE" => SILENT
+    "ERRMODE" => EXCEPTION
     "PERSISTENT" => false
     "DRIVER_NAME" => "sqlite"
     "ORACLE_NULLS" => NATURAL
diff --git a/src/Symfony/Component/VarDumper/Tests/Caster/ReflectionCasterTest.php b/src/Symfony/Component/VarDumper/Tests/Caster/ReflectionCasterTest.php
index 15f0b4e61d..293afd94eb 100644
--- a/src/Symfony/Component/VarDumper/Tests/Caster/ReflectionCasterTest.php
+++ b/src/Symfony/Component/VarDumper/Tests/Caster/ReflectionCasterTest.php
@@ -49,8 +49,8 @@ ReflectionClass {
 %A]
   methods: array:%d [
 %A
-    "export" => ReflectionMethod {
-      +name: "export"
+    "__construct" => ReflectionMethod {
+      +name: "__construct"
       +class: "ReflectionClass"
 %A    parameters: {
         $%s: ReflectionParameter {
diff --git a/src/Symfony/Component/VarDumper/Tests/Caster/SplCasterTest.php b/src/Symfony/Component/VarDumper/Tests/Caster/SplCasterTest.php
index e26c371d72..24701be411 100644
--- a/src/Symfony/Component/VarDumper/Tests/Caster/SplCasterTest.php
+++ b/src/Symfony/Component/VarDumper/Tests/Caster/SplCasterTest.php
@@ -172,14 +172,17 @@ EOTXT;
         $expected = <<<EOTXT
 ArrayObject {
   +"foo": 234
+  -storage: array:1 [
+    0 => 123
+  ]
   flag::STD_PROP_LIST: false
   flag::ARRAY_AS_PROPS: false
   iteratorClass: "ArrayIterator"
-  storage: array:1 [
-    0 => 123
-  ]
 }
 EOTXT;
+        if (\PHP_VERSION_ID < 70400) {
+            $expected = str_replace('-storage:', 'storage:', $expected);
+        }
         $this->assertDumpEquals($expected, $var);
     }
 
@@ -190,13 +193,16 @@ EOTXT;
         $expected = <<<EOTXT
 Symfony\Component\VarDumper\Tests\Caster\MyArrayIterator {
   -foo: 123
-  flag::STD_PROP_LIST: false
-  flag::ARRAY_AS_PROPS: false
-  storage: array:1 [
+  -storage: array:1 [
     0 => 234
   ]
+  flag::STD_PROP_LIST: false
+  flag::ARRAY_AS_PROPS: false
 }
 EOTXT;
+        if (\PHP_VERSION_ID < 70400) {
+            $expected = str_replace('-storage:', 'storage:', $expected);
+        }
         $this->assertDumpEquals($expected, $var);
     }
 
diff --git a/src/Symfony/Component/VarDumper/Tests/Dumper/CliDumperTest.php b/src/Symfony/Component/VarDumper/Tests/Dumper/CliDumperTest.php
index 4f3b73f432..7c2c058a02 100644
--- a/src/Symfony/Component/VarDumper/Tests/Dumper/CliDumperTest.php
+++ b/src/Symfony/Component/VarDumper/Tests/Dumper/CliDumperTest.php
@@ -199,6 +199,7 @@ EOTXT;
 
     /**
      * @requires extension xml
+     * @requires PHP < 8.0
      */
     public function testXmlResource()
     {
diff --git a/src/Symfony/Component/VarDumper/composer.json b/src/Symfony/Component/VarDumper/composer.json
index bee166a790..3ce7cef280 100644
--- a/src/Symfony/Component/VarDumper/composer.json
+++ b/src/Symfony/Component/VarDumper/composer.json
@@ -18,7 +18,8 @@
     "require": {
         "php": ">=7.1.3",
         "symfony/polyfill-mbstring": "~1.0",
-        "symfony/polyfill-php72": "~1.5"
+        "symfony/polyfill-php72": "~1.5",
+        "symfony/polyfill-php80": "^1.15"
     },
     "require-dev": {
         "ext-iconv": "*",