Move HasOffset generalization logic into the type classes themselves

Instead of hardcoding `new MixedType()` in TemplateTypeHelper, add
`generalize(GeneralizePrecision::templateArgument())` overrides to
HasOffsetValueType and HasOffsetType that return MixedType. The
TypeTraverser in generalizeInferredTemplateType now delegates to
the type's own generalize() method.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Type/Accessory/HasOffsetType.php

@@ -13,6 +13,7 @@
 use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\Enum\EnumCaseObjectType;
 use PHPStan\Type\ErrorType;
+use PHPStan\Type\GeneralizePrecision;
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\IsSuperTypeOfResult;
@@ -44,7 +45,9 @@ class HasOffsetType implements CompoundType, AccessoryType
 	use NonGenericTypeTrait;
 	use UndecidedComparisonCompoundTypeTrait;
 	use NonRemoveableTypeTrait;
-	use NonGeneralizableTypeTrait;
+	use NonGeneralizableTypeTrait {
+		generalize as traitGeneralize;
+	}
 
 	/**
 	 * @api
@@ -53,6 +56,15 @@ public function __construct(private ConstantStringType|ConstantIntegerType $offs
 	{
 	}
 
+	public function generalize(GeneralizePrecision $precision): Type
+	{
+		if ($precision->isTemplateArgument()) {
+			return new MixedType();
+		}
+
+		return $this->traitGeneralize($precision);
+	}
+
 	public function getOffsetType(): ConstantStringType|ConstantIntegerType
 	{
 		return $this->offsetType;

src/Type/Accessory/HasOffsetValueType.php

@@ -15,6 +15,7 @@
 use PHPStan\Type\ConstantScalarType;
 use PHPStan\Type\Enum\EnumCaseObjectType;
 use PHPStan\Type\ErrorType;
+use PHPStan\Type\GeneralizePrecision;
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\IntersectionType;
@@ -48,12 +49,23 @@ class HasOffsetValueType implements CompoundType, AccessoryType
 	use NonGenericTypeTrait;
 	use UndecidedComparisonCompoundTypeTrait;
 	use NonRemoveableTypeTrait;
-	use NonGeneralizableTypeTrait;
+	use NonGeneralizableTypeTrait {
+		generalize as traitGeneralize;
+	}
 
 	public function __construct(private ConstantStringType|ConstantIntegerType $offsetType, private Type $valueType)
 	{
 	}
 
+	public function generalize(GeneralizePrecision $precision): Type
+	{
+		if ($precision->isTemplateArgument()) {
+			return new MixedType();
+		}
+
+		return $this->traitGeneralize($precision);
+	}
+
 	public function getOffsetType(): ConstantStringType|ConstantIntegerType
 	{
 		return $this->offsetType;

src/Type/Generic/TemplateTypeHelper.php

@@ -7,7 +7,6 @@
 use PHPStan\Type\Accessory\HasOffsetValueType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\GeneralizePrecision;
-use PHPStan\Type\MixedType;
 use PHPStan\Type\NonAcceptingNeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeTraverser;
@@ -153,7 +152,7 @@ public static function generalizeInferredTemplateType(TemplateType $templateType
 
 			$type = TypeTraverser::map($type, static function (Type $type, callable $traverse): Type {
 				if ($type instanceof HasOffsetValueType || $type instanceof HasOffsetType) {
-					return new MixedType();
+					return $type->generalize(GeneralizePrecision::templateArgument());
 				}
 
 				return $traverse($type);