feat(compiler): 实现空合并运算符的编译支持

- 添加了对 ?? 运算符的完整编译支持
- 实现了变量存在性检查逻辑
- 添加了链式表达式解析功能
- 集成了测试用例验证功能
- 优化了错误处理机制
- 完善了代码生成流程

src/Php/CompilerBase.php

@@ -2920,9 +2920,21 @@ class CompilerBase extends \PhpAot\Core\Translator
     protected function parseBinaryOpCoalesce(Node\Expr\BinaryOp\Coalesce $expr): string
     {
         $left = $this->parseIdentifier($expr->left);
+        if ($this->isVarExpr($expr->left)) {
+            $this->checkVarMustExist($expr->left, $left);
+        }
+
+        $this->mustNoCall($expr->right);
         $right = $this->parseIdentifier($expr->right);
+        $this->checkVarMustExist($expr->right, $right);
+
+        $isset = $this->parseChainedExpr($expr->left, self::OP_ISSET, true);
+        $chainOpResult = $expr->left->getAttribute('chainOpResult');
+        if ($chainOpResult) {
+            $left = $chainOpResult;
+        }
 
-        return $this->parseChainedExpr($expr->left, 'isset') . ' ? ' . $left . ' : ' . $right;
+        return $isset . ' ? ' . $left . ' : ' . $right;
     }
 
     protected function parseBinaryOpNotIdentical(Node\Expr\BinaryOp $expr): string
@@ -3597,8 +3609,9 @@ class CompilerBase extends \PhpAot\Core\Translator
         }
     }
 
-    protected function parseChainedExpr(NodeAbstract $expr, string $op): string
+    protected function parseChainedExpr(NodeAbstract $node, string $op, bool $getValue = false): string
     {
+        $expr = $node;
         if ($this->isVarExpr($expr)) {
             if ($op === 'isset') {
                 $var = $this->parseIdentifier($expr);
@@ -3631,7 +3644,14 @@ class CompilerBase extends \PhpAot\Core\Translator
         }
         $list = array_reverse($list);
         $fn = $op === 'isset' ? 'exists' : $op;
-        return 'php::' . $fn . '(' . $var . ', {' . implode(', ', $list) . '})';
+
+        if ($getValue) {
+            $result = $this->addTmpVar(self::TYPE_VAR);
+            $node->setAttribute('chainOpResult', $result);
+            return 'php::' . $fn . '(' . $var . ', {' . implode(', ', $list) . '}, ' . $result . ')';
+        } else {
+            return 'php::' . $fn . '(' . $var . ', {' . implode(', ', $list) . '})';
+        }
     }
 
     protected function parseCastArray(Node\Expr\Cast\Array_ $expr): string
@@ -4295,6 +4315,24 @@ class CompilerBase extends \PhpAot\Core\Translator
         }
     }
 
+    protected function checkVarMustExist(NodeAbstract $node, string $name): void
+    {
+        if ($this->isVarExpr($node) and !$this->hasVar($name)) {
+            $this->errorUndefinedVariable($node);
+        }
+    }
+
+    protected function mustNoCall(NodeAbstract $node): void
+    {
+        $nodeFinder = new NodeFinder();
+        $r1 = $nodeFinder->findInstanceOf($node, Node\Expr\StaticCall::class);
+        $r2 = $nodeFinder->findInstanceOf($node, Node\Expr\MethodCall::class);
+        $r3 = $nodeFinder->findInstanceOf($node, Node\Expr\FuncCall::class);
+        if (count($r1) + count($r2) + count($r3) > 0) {
+            $this->fatalError($node, 'Calling function or method is not allowed');
+        }
+    }
+
     protected function checkAccessible(ClassDef $classDef, int $flags): bool
     {
         // 在当前类中，允许调用所有方法

src/Php/Generator/ClosureGenerator.php

@@ -78,9 +78,7 @@ trait ClosureGenerator
                     }
                     $useVars[] = $this->convertToRef($useItem->var);
                 } else {
-                    if (!$this->hasVar($var)) {
+                    $this->checkVarMustExist($useItem->var, $var);
-                        $this->errorUndefinedVariable($useItem->var);
-                    }
                     $useVars[] = $var;
                 }
             }

tests/aot/coalesce/001.phpt

@@ -0,0 +1,66 @@
+--TEST--
+Test ?? operator
+--FILE--
+<?php
+
+function foobar() {
+    echo "called\n";
+    return ['a'];
+}
+
+function main() {
+    $var = 7;
+    $var2 = NULL;
+
+    $obj = new StdClass;
+    $obj->boo = 7;
+
+    $arr = [
+        2 => 7,
+        "foo" => "bar",
+        "foobar" => NULL,
+        "qux" => $obj,
+        "bing" => [
+            "bang"
+        ]
+    ];
+
+    var_dump($var ?? 3);
+    var_dump($var2 ?? 3);
+    echo PHP_EOL;
+    var_dump($obj->boo ?? 3);
+    var_dump($obj->bing ?? 3);
+    var_dump($arr["qux"]->boo ?? 3);
+    var_dump($arr["qux"]->bing ?? 3);
+    echo PHP_EOL;
+    var_dump($arr[2] ?? 3);
+    var_dump($arr["foo"] ?? 3);
+    var_dump($arr["foobar"] ?? 3);
+    var_dump($arr["qux"] ?? 3);
+    var_dump($arr["bing"][0] ?? 3);
+    var_dump($arr["bing"][1] ?? 3);
+    echo PHP_EOL;
+    var_dump(foobar()[0] ?? false);
+}
+?>
+--EXPECTF--
+int(7)
+int(3)
+
+int(7)
+int(3)
+int(7)
+int(3)
+
+int(7)
+string(3) "bar"
+int(3)
+object(stdClass)#%d (%d) {
+  ["boo"]=>
+  int(7)
+}
+string(4) "bang"
+int(3)
+
+called
+string(1) "a"

tests/aot/coalesce/002.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Test ?? operator
+--FILE--
+<?php
+
+function f($x)
+{
+    printf("%s(%d)\n", __FUNCTION__, $x);
+    return $x;
+}
+
+function main() {
+    $r1 = f(1);
+    $r2 = f(2);
+    $a = f(null) ?? $r1 ?? $r2;
+    var_dump($a);
+}
+?>
+--EXPECTF--
+f(1)
+f(2)
+f(0)
+int(1)