feat(compiler): 添加对孤立代码的检测和错误处理

- 在 CompilerBase 中添加 foundStrayCode 方法用于报告孤立代码错误
- 在 Preprocessor 中为 Stmt_Expression 类型添加孤立代码检测
- 防止在扩展模式下生成名为 main 的函数
- 添加 empty-2.phpt 测试用例验证空值合并操作符功能

examples/autoload_class.php

@@ -11,3 +11,5 @@ function main()
     $o = new CpuCoreCounter();
     var_dump($o->getCount());
 }
+
+test();

src/Php/CompilerBase.php

@@ -1799,6 +1799,11 @@ class CompilerBase extends \PhpAot\Core\Translator
         return false;
     }
 
+    protected function foundStrayCode(): never
+    {
+        $this->error("All execution code must be within a function; there is no allowance for stray code.");
+    }
+
     protected function parseFuncCall(Node\Expr\FuncCall $expr, bool $silent = false): string
     {
         $call = '';

src/Php/Preprocessor.php

@@ -105,9 +105,10 @@ class Preprocessor extends CompilerBase
                 case 'Stmt_Const':
                     $this->parseConstDef($v);
                     break;
+                case 'Stmt_Expression':
+                    $this->foundStrayCode();
                 default:
                     $this->fatalError($v, 'Unsupported statement: ' . $type);
-                    break;
             }
         }
 
@@ -142,6 +143,8 @@ class Preprocessor extends CompilerBase
                 case 'Stmt_Use':
                 case 'Stmt_Const':
                     break;
+                case 'Stmt_Expression':
+                    $this->foundStrayCode();
                 default:
                     abort($v2);
             }
@@ -174,6 +177,8 @@ class Preprocessor extends CompilerBase
                 case 'Stmt_ClassMethod':
                     $code .= $this->prepareFunction($v) . PHP_EOL;
                     break;
+                case 'Stmt_Expression':
+                    $this->foundStrayCode();
                 default:
                     abort($v);
             }

src/template/extension.cc.php

@@ -72,6 +72,9 @@ endforeach;
 static const zend_function_entry ext_functions[] = {
 <?php
 foreach ($this->functions as $functionDef):
+    if ($this->buildMode === 'ext' and $functionDef->name === 'main') {
+        continue;
+    }
 ?>
     ZEND_FE(<?=$functionDef->name?>, arginfo_<?=$functionDef->name?>)
 <?php endforeach;?>

tests/aot/empty-2.phpt

@@ -0,0 +1,15 @@
+--TEST--
+empty 2
+--FILE--
+<?php
+$a = 0;
+$b = $a ?: 1;
+var_dump($b);
+
+$c = 3;
+$d = $c ?: 5;
+var_dump($d);
+?>
+--EXPECT--
+int(1)
+int(3)