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resolveTemplateTypes() swaps template types by name, so when K resolves to itself, a narrowed K got replaced by the declared one. For example, with K of string|int|object the key of array<K, V> is K of int|string. The PHPDoc return type then didn't fit the native array type and we fell back to plain array. This only started affecting conditional return types in 2.2.16. Before that ConditionalType::traverse() re-normalized its branches, which narrowed the key again and hid the problem.
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Closes phpstan/phpstan#15321
resolveTemplateTypes()replaces template types by name. When the class's own template map resolvesKto itself, a narrowed occurrence like theK of int|stringkey ofarray<K, V>gets replaced by the declaredK of string|int|object.TypehintHelper::decideType()then resolves that toarray<int|object|string, mixed>, which doesn't fit the nativearray, so we end up with plainarray.Plain
@return array<K, V>has been broken like this for a while. The conditional return type only broke in 2.2.16: since 8411207,ConditionalType::traverse()keeps the traversed branches instead of normalizing them again, and that re-normalization used to narrow the key back.The fix keeps the occurrence when the standin is the same template type (same name and scope, not an argument).
nsrt/bug-15321.phpfails on all 5 assertions without the change.