fix(php): 解决数组取消设置时空维度的错误处理

- 在数组维度获取为空时添加致命错误提示
- 添加对 unset($arr[]) 语法的错误检测
- 新增对应的单元测试验证空数组维度取消设置的错误情况
- 创建测试文件验证数组取消设置的边界情况

phpunit/code/unset-array-dim-fetch-empty.php

@@ -0,0 +1,6 @@
+<?php
+function main()
+{
+    $arr = [];
+    unset($arr[]);
+}

phpunit/src/UndefineTest.php

@@ -7,4 +7,9 @@ class UndefineTest extends \BaseTest
         $this->exec('The variable `$u1` is undefined', 'undefined-vars-01.php');
         $this->exec('Unsupported unset type `Expr_FuncCall`', 'unset-01.php');
     }
+
+    public function testUnsetEmptyArrayDimFetch()
+    {
+        $this->exec('Cannot use [] for array unset', 'unset-array-dim-fetch-empty.php');
+    }
 }

src/Php/CompilerBase.php

@@ -4037,6 +4037,9 @@ class CompilerBase extends \PhpAot\Core\Translator
         $lines = [];
         foreach ($vars as $var) {
             if ($this->isArrayDimFetch($var)) {
+                if ($var->dim === null) {
+                    $this->fatalError($var, 'Cannot use [] for array unset');
+                }
                 $array = $this->parseIdentifier($var->var);
                 $dim = $this->parseIdentifier($var->dim);
                 $lines[] = $array . '.offsetUnset(' . $dim . ');';