feat(enum): 支持枚举类型解析和处理

- 添加了枚举类型的语法解析功能
- 实现了对带值枚举（backed enums）的支持
- 添加了枚举案例值的存储和访问机制
- 支持枚举类型的运行时对象处理
- 完善了枚举常量数组的生成逻辑
- 新增了多个枚举相关的测试用例

src/Php/Entity/ClassDef.php

@@ -32,6 +32,17 @@ class ClassDef extends ClassLikeDef
     public string $extends = '';
     public bool $requireCtor = false;
     public bool $enum = false;
+
+    /**
+     * Backing type for backed enums ('int' or 'string'), null for pure enums.
+     */
+    public ?string $enumBackingType = null;
+
+    /**
+     * Enum cases: case name => backing value (int/string for backed enums, null for pure enums).
+     * @var array<string, int|string|null>
+     */
+    public array $enumCases = [];
     public ?Trait_ $trait = null;
 
     /**

src/Php/Preprocessor.php

@@ -438,6 +438,9 @@ class Preprocessor extends CompilerBase
 
         if ($class instanceof Node\Stmt\Enum_) {
             $this->classDef->enum = true;
+            if ($class->scalarType !== null) {
+                $this->classDef->enumBackingType = $class->scalarType->name;
+            }
         }
         if (!$class instanceof Node\Stmt\Trait_) {
             $this->classDef->implements = $this->parseImplements($class->implements);
@@ -464,7 +467,10 @@ class Preprocessor extends CompilerBase
                     $this->prepareTraitUse($v);
                     break;
                 case 'Stmt_Nop':
+                    break;
                 case 'Stmt_EnumCase':
+                    $caseName = $this->parseIdentifier($v->name);
+                    $this->classDef->enumCases[$caseName] = $v->expr?->value;
                     break;
                 case 'Stmt_ClassMethod':
                     $this->prepareClassMethod($v, $class);

src/Php/Translator.php

@@ -1518,6 +1518,17 @@ CODE;
                 return $this->genCValue(constant($constName));
             }
         }
+        // Resolve enum case references. Enum cases are runtime objects; their
+        // actual values in class constant arrays are set at runtime by
+        // genClassArrayConstants() via php::getEnumCase(). Return the backing
+        // value as a placeholder so gen_stub.php's ConstExprEvaluator can complete.
+        if ($this->hasClass($class)) {
+            $classDef = $this->getClass($class);
+            if ($classDef->enum && array_key_exists($name, $classDef->enumCases)) {
+                $caseValue = $classDef->enumCases[$name];
+                return $this->genCValue($caseValue ?? $name);
+            }
+        }
         $this->fatalError($expr, "Class constant `{$class}::{$name}` not found");
     }
 

tests/aot/enum/3.phpt

@@ -0,0 +1,41 @@
+--TEST--
+enum 2
+--FILE--
+<?php
+enum T: string
+{
+    case I = 'int';
+    case S = 'string';
+}
+
+final class TestSpa
+{
+    private const F = [
+        '1' => ['d' => '', 't' => T::S],
+        '2' => ['d' => 1, 't' => T::I],
+        '3' => ['d' => 123, 't' => T::S],
+    ];
+
+    public static function E(): array
+    {
+        return self::F;
+    }
+}
+
+function main()
+{
+    foreach (TestSpa::E() as $n => $f) {
+
+        $ok = match ($f['t']) {
+            T::I    => is_int($f['d']),
+            T::S => is_string($f['d']),
+        };
+
+        echo $ok? " pass {$n} => [{$f['d']}, {$f['t']->value}]\n": " fail {$n} 元组非法\n";
+    }
+}
+?>
+--EXPECT--
+pass 1 => [, string]
+ pass 2 => [1, int]
+ fail 3 元组非法

tests/aot/enum/4.phpt

@@ -0,0 +1,30 @@
+--TEST--
+enum 2
+--FILE--
+<?php
+enum TestEnum
+{
+    case FOO;
+    case BAR;
+}
+
+final class TestSpa
+{
+    public const F = [
+        TestEnum::FOO,
+        TestEnum::BAR,
+    ];
+}
+
+function main()
+{
+    var_dump(TestSpa::F);
+}
+?>
+--EXPECT--
+array(2) {
+  [0]=>
+  enum(TestEnum::FOO)
+  [1]=>
+  enum(TestEnum::BAR)
+}

tests/aot/enum/5.phpt

@@ -0,0 +1,31 @@
+--TEST--
+enum 2
+--FILE--
+<?php
+enum TestEnum: string
+{
+    case FOO = TestSpa::F;
+    case BAR = 'bar';
+}
+
+final class TestSpa
+{
+    public const F = 'foo';
+}
+
+function main()
+{
+    var_dump(TestEnum::cases());
+    var_dump(TestEnum::FOO);
+    var_dump((string) TestEnum::FOO->value);
+}
+?>
+--EXPECT--
+array(2) {
+  [0]=>
+  enum(TestEnum::FOO)
+  [1]=>
+  enum(TestEnum::BAR)
+}
+enum(TestEnum::FOO)
+string(3) "foo"