Fix phpstan/phpstan#7170: Can not set optional array element to explicit value in generic#5335
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…c 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
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Summary
When a template type is bounded by a constant array with optional keys (e.g.
@template Tdata of array{extension?: array<mixed>}), setting an optional key's value inside the class produced a false positive "does not accept" error. The same code without generics worked fine.Changes
setOffsetValueType,setExistingOffsetValueType, andunsetOffsetinsrc/Type/Generic/TemplateConstantArrayType.phpto preserve the template type wrapper when the result of the parent operation is still compatible with the template's boundtestBug7170intests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.phptests/PHPStan/Rules/Properties/data/bug-7170.phpRoot cause
TemplateConstantArrayTypeextendsConstantArrayTypebut did not overridesetOffsetValueType. When called, the parentConstantArrayType::setOffsetValueTypeusedConstantArrayTypeBuilderwhich returned a plainConstantArrayType, completely losing the template wrapper. The resulting concrete type (e.g.array{extension: array{}}) was then checked against the property's template typeTdatausingTemplateTypeParameterStrategy, which rejected it because a concrete type is not the same as the template type.The fix checks whether the result of the parent operation is still within the template's bound. If so, the template type itself is returned, preserving the template wrapper and allowing the property assignment to succeed.
Test
The regression test reproduces the original issue: a generic class with
@template Tdata of array{extension?: array<mixed>}that sets$this->data['extension'] = []inside an!issetguard. The test expects no errors, matching the behavior of the equivalent non-generic class.Fixes phpstan/phpstan#7170