Fix false positive when setting optional array offset on template constant array property

- Override setOffsetValueType() and setExistingOffsetValueType() in TemplateConstantArrayType
- When the offset exists in the template's bound and the value type is accepted by the bound's value type, return the template type itself
- This preserves the template contract: modifying an in-bound offset on a template value still produces a valid template value
- New regression test in tests/PHPStan/Rules/Properties/data/bug-7170.php

Closes phpstan/phpstan#7170

Author: phpstan-bot

src/Type/Generic/TemplateConstantArrayType.php

@@ -35,4 +35,42 @@ public function __construct(
 		$this->default = $default;
 	}
 
+	public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $unionValues = true): Type
+	{
+		if ($this->isOffsetWithinBound($offsetType, $valueType)) {
+			return $this;
+		}
+
+		return parent::setOffsetValueType($offsetType, $valueType, $unionValues);
+	}
+
+	public function setExistingOffsetValueType(Type $offsetType, Type $valueType): Type
+	{
+		if ($this->isOffsetWithinBound($offsetType, $valueType)) {
+			return $this;
+		}
+
+		return parent::setExistingOffsetValueType($offsetType, $valueType);
+	}
+
+	private function isOffsetWithinBound(?Type $offsetType, Type $valueType): bool
+	{
+		if ($offsetType === null) {
+			return false;
+		}
+
+		$boundKeyTypes = $this->bound->getKeyTypes();
+		$boundValueTypes = $this->bound->getValueTypes();
+
+		foreach ($boundKeyTypes as $i => $boundKeyType) {
+			if (!$offsetType->equals($boundKeyType)) {
+				continue;
+			}
+
+			return $boundValueTypes[$i]->accepts($valueType, true)->yes();
+		}
+
+		return false;
+	}
+
 }

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -1003,4 +1003,9 @@ public function testCloneWith(): void
 		]);
 	}
 
+	public function testBug7170(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-7170.php'], []);
+	}
+
 }

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'] = [];
+		}
+	}
+}