From 0da07cb06505af8dd665ecdbe18975417220c2ef Mon Sep 17 00:00:00 2001
From: Yurun <admin@yurunsoft.com>
Date: Wed, 15 Jul 2026 19:06:49 +0800
Subject: [PATCH] =?UTF-8?q?fix(compiler):=20=E4=BF=AE=E5=A4=8D=E5=AF=B9?=
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---
 src/Parser/AssignOpTrait.php                       | 14 +++++++++++---
 .../coalesce/assign-coalesce-undefined-var.phpt    | 14 ++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)
 create mode 100644 tests/compiler/coalesce/assign-coalesce-undefined-var.phpt

diff --git a/src/Parser/AssignOpTrait.php b/src/Parser/AssignOpTrait.php
index cf826761..826cd011 100644
--- a/src/Parser/AssignOpTrait.php
+++ b/src/Parser/AssignOpTrait.php
@@ -862,6 +862,17 @@ trait AssignOpTrait
     protected function parseAssignOpCoalesce(Expr\AssignOp\Coalesce $expr): string
     {
         $this->checkLeftValue($expr->var);
+
+        // PHP 允许对未定义的简单变量使用 ??=（例如 `$a ??= 123`）：
+        // 此时 isset 为 false，直接执行赋值。需要提前声明该局部变量，
+        // 否则 isset 检查会因变量未定义而报错。此处必须声明为 Type::VAR
+        // （Variant），使其初值为 NULL，从而 isset 在运行时正确判定为
+        // false 并执行赋值；若使用原生类型，isset 恒为 true 会导致取到
+        // 未初始化的默认值（如 int(0)、空字符串）。
+        if ($this->isVarExpr($expr->var) and !$this->hasVar($this->parseIdentifier($expr->var))) {
+            $this->addLocalVar($this->parseIdentifier($expr->var), Type::VAR);
+        }
+
         $isset = $this->parseChainedExpr($expr->var, self::OP_ISSET);
 
         $var = $this->parseWritableIdentifier($expr->var);
@@ -878,9 +889,6 @@ trait AssignOpTrait
         if ($this->isVarExpr($expr->expr) and !$this->hasVar($right)) {
             $this->errorUndefinedVariable($expr->expr);
         }
-        if ($this->isVarExpr($expr->var) and !$this->hasVar($var)) {
-            $this->addLocalVar($var, $this->getNormalAssignType($this->detectTypeOfExpr($expr->expr)));
-        }
         return '(' . $isset . '?' . $var . ':(' . $var . ' = ' . $right . '))';
     }
 
diff --git a/tests/compiler/coalesce/assign-coalesce-undefined-var.phpt b/tests/compiler/coalesce/assign-coalesce-undefined-var.phpt
new file mode 100644
index 00000000..4aad8edb
--- /dev/null
+++ b/tests/compiler/coalesce/assign-coalesce-undefined-var.phpt
@@ -0,0 +1,14 @@
+--TEST--
+assign coalesce on undefined variable
+--FILE--
+<?php
+$a ??= 123;
+var_dump($a);
+
+$b ??= 'foo';
+$b ??= 'bar';
+var_dump($b);
+?>
+--EXPECT--
+int(123)
+string(3) "foo"