From 1746506b4329d8f1455d54a61a5e13ed6bc044eb Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sun, 29 Mar 2026 23:05:53 +0000
Subject: [PATCH] Fix phpstan/phpstan#7170: Cannot set optional array element
 in generic class

- Override setOffsetValueType, setExistingOffsetValueType, and unsetOffset in TemplateConstantArrayType to preserve the template wrapper when the result is compatible with the bound
- The root cause was that ConstantArrayType::setOffsetValueType returned a plain ConstantArrayType, losing the template context, which then failed the template parameter acceptance check
- New regression test in tests/PHPStan/Rules/Properties/data/bug-7170.php
---
 .../Generic/TemplateConstantArrayType.php     | 33 ++++++++++++++
 .../TypesAssignedToPropertiesRuleTest.php     |  5 +++
 .../Rules/Properties/data/bug-7170.php        | 44 +++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 tests/PHPStan/Rules/Properties/data/bug-7170.php

diff --git a/src/Type/Generic/TemplateConstantArrayType.php b/src/Type/Generic/TemplateConstantArrayType.php
index fbc13bad6d0..9cdae5ec6b6 100644
--- a/src/Type/Generic/TemplateConstantArrayType.php
+++ b/src/Type/Generic/TemplateConstantArrayType.php
@@ -35,4 +35,37 @@ public function __construct(
 		$this->default = $default;
 	}
 
+	public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $unionValues = true): Type
+	{
+		$result = parent::setOffsetValueType($offsetType, $valueType, $unionValues);
+
+		if ($this->getBound()->isSuperTypeOf($result)->yes()) {
+			return $this;
+		}
+
+		return $result;
+	}
+
+	public function setExistingOffsetValueType(Type $offsetType, Type $valueType): Type
+	{
+		$result = parent::setExistingOffsetValueType($offsetType, $valueType);
+
+		if ($this->getBound()->isSuperTypeOf($result)->yes()) {
+			return $this;
+		}
+
+		return $result;
+	}
+
+	public function unsetOffset(Type $offsetType, bool $preserveListCertainty = false): Type
+	{
+		$result = parent::unsetOffset($offsetType, $preserveListCertainty);
+
+		if ($this->getBound()->isSuperTypeOf($result)->yes()) {
+			return $this;
+		}
+
+		return $result;
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php b/tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php
index 88b2bb4a2c6..f9ec8d6a4bf 100644
--- a/tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php
+++ b/tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php
@@ -1055,4 +1055,9 @@ public function testBug10924(): void
 		$this->analyse([__DIR__ . '/../Methods/data/bug-10924.php'], []);
 	}
 
+	public function testBug7170(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-7170.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Properties/data/bug-7170.php b/tests/PHPStan/Rules/Properties/data/bug-7170.php
new file mode 100644
index 00000000000..1953273a595
--- /dev/null
+++ b/tests/PHPStan/Rules/Properties/data/bug-7170.php
@@ -0,0 +1,44 @@
+<?php declare(strict_types=1);
+
+namespace Bug7170;
+
+/**
+ * @template Tdata of array{extension?: array<mixed>}
+ */
+class Data
+{
+	/**
+	 * @var Tdata
+	 */
+	private $data;
+
+	/**
+     * @param Tdata $data
+     */
+    public function __construct(array $data = [])
+    {
+        $this->data = $data;
+    }
+
+
+    public function setExtensionProperty(): void
+    {
+        if (!isset($this->data['extension'])) {
+            $this->data['extension'] = [];
+        }
+    }
+}
+
+class NonGeneric
+{
+	/**
+	 * @var array{extension?: array<mixed>}
+	 */
+	private $data;
+	public function setData(): void
+	{
+		if (!isset($this->data['extension'])) {
+			$this->data['extension'] = [];
+		}
+	}
+}