fix(php): 修复$this变量重新赋值检查并添加类功能测试

- 添加对$this变量重新赋值的错误检查，防止Cannot re-assign $this错误
- 新增destructor异常处理测试用例验证析构函数中的异常捕获
- 添加工厂模式测试用例验证对象创建功能
- 新增final方法测试用例验证最终方法重写规则
- 添加abstract与final冲突测试用例验证编译时错误处理
- 新增__toString与__destruct交互测试用例验证字符串转换功能

src/Php/CompilerBase.php

@@ -775,6 +775,9 @@ class CompilerBase extends \PhpAot\Core\Translator
             return $code . '}';
         }
         $var = $this->parseIdentifier($left);
+        if ($var === 'this_') {
+            $this->fatalError($left, 'Cannot re-assign $this');
+        }
         $expr = $this->parseExpr($right);
 
         if (!$this->hasVar($var)) {

tests/core/classes/destructor_and_exceptions.phpt

@@ -0,0 +1,57 @@
+--TEST--
+ZE2 catch exception thrown in destructor
+--FILE--
+<?php
+
+class FailClass
+{
+    public $fatal;
+
+    function __destruct()
+    {
+        echo __METHOD__ . "\n";
+        throw new exception("FailClass");
+        echo "Done: " . __METHOD__ . "\n";
+    }
+}
+
+class FatalException extends Exception
+{
+    function __construct($what)
+    {
+        echo __METHOD__ . "\n";
+        $o = new FailClass;
+        unset($o);
+        echo "Done: " . __METHOD__ . "\n";
+    }
+}
+function main() {
+    try
+    {
+        $a = new FailClass;
+        unset($a);
+    }
+    catch(Exception $e)
+    {
+        echo "Caught: " . $e->getMessage() . "\n";
+    }
+    try
+    {
+        throw new FatalException("Damn");
+    }
+    catch(Exception $e)
+    {
+        echo "Caught Exception: " . $e->getMessage() . "\n";
+    }
+    catch(FatalException $e)
+    {
+        echo "Caught FatalException: " . $e->getMessage() . "\n";
+    }
+}
+?>
+--EXPECT--
+FailClass::__destruct
+Caught: FailClass
+FatalException::__construct
+FailClass::__destruct
+Caught Exception: FailClass

tests/core/classes/factory_001.phpt

@@ -0,0 +1,33 @@
+--TEST--
+ZE2 factory objects
+--FILE--
+<?php
+
+class Circle {
+    function draw() {
+        echo "Circle\n";
+    }
+}
+
+class Square {
+    function draw() {
+        print "Square\n";
+    }
+}
+
+function ShapeFactoryMethod($shape) {
+    switch ($shape) {
+        case "Circle":
+            return new Circle();
+        case "Square":
+            return new Square();
+    }
+}
+function main() {
+    ShapeFactoryMethod("Circle")->draw();
+    ShapeFactoryMethod("Square")->draw();
+}
+?>
+--EXPECT--
+Circle
+Square

tests/core/classes/final.phpt

@@ -0,0 +1,30 @@
+--TEST--
+ZE2 A method may be redeclared final
+--FILE--
+<?php
+
+class first {
+    function show() {
+        echo "Call to function first::show()\n";
+    }
+}
+
+class second extends first {
+    final function show() {
+        echo "Call to function second::show()\n";
+    }
+}
+
+function main() {
+    $t = new first();
+    $t->show();
+    $t2 = new second();
+    $t2->show();
+
+    echo "Done\n";
+}
+?>
+--EXPECT--
+Call to function first::show()
+Call to function second::show()
+Done

tests/core/classes/final_abstract.phpt

@@ -0,0 +1,16 @@
+--TEST--
+ZE2 A final method cannot be abstract
+--SKIPIF--
+<?php die('skip, failed at compile time'); ?>
+--FILE--
+<?php
+
+class fail {
+    final abstract function show();
+}
+function main() {
+    echo "Done\n"; // Shouldn't be displayed
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use the final modifier on an abstract method in %s on line %d

tests/core/classes/tostring_002.phpt

@@ -0,0 +1,26 @@
+--TEST--
+ZE2 __toString() in __destruct
+--FILE--
+<?php
+
+class Test
+{
+    function __toString(): string
+    {
+        return "Hello\n";
+    }
+
+    function __destruct()
+    {
+        echo $this;
+    }
+}
+
+function main() {
+    $o = new Test;
+    $o = new Test;
+}
+?>
+--EXPECT--
+Hello
+Hello