Change GenericObjectType generics via TypeSpecifyingExtension #6620
Description
Feature request
In my use case, I have partly successfull already implemented in staabm/phpstan-dba#258, I have the following scenario.
A PDOStatement class is specifed via a return type extension of PdoStatement->query() like
$query = 'SELECT email, adaid FROM ada';
$stmt = $pdo->query($query, PDO::FETCH_NUM);
assertType('PDOStatement<array{string, int<0, 4294967295>}>', $stmt);to implement support for PDO native PDOStatement->setFetchType() I am using a MethodTypeSpecifyingExtension to support
$query = 'SELECT email, adaid FROM ada';
$stmt = $pdo->query($query, PDO::FETCH_NUM);
assertType('PDOStatement<array{string, int<0, 4294967295>}>', $stmt);
$stmt->setFetchMode(PDO::FETCH_ASSOC);
assertType('PDOStatement<array{email: string, adaid: int<0, 4294967295>}>', $stmt);.. so the idea is to turn a PDOStatement<array{string, int<0, 4294967295>}> into a PDOStatement<array{email: string, adaid: int<0, 4294967295>}> - and suprisingly this worked - from a phpunit point of view regarding assertType.
it has a negative side-effect though, that the ImpossibleCheckTypeHelper realizes a incompatibility between the generic-type before/after the specifying extension does what it is supposed to do.
in the above scenario $isSuperType->no() is true and therefore we run into the return false case.
this return false triggers the following case
which makes phpstan error like
Call to method PDOStatement<array<int|string, int<0, 4294967295>|string>,array<int|string,
int<0, 4294967295>|string>>::setFetchMode() with 3 will always evaluate to false.
I create this issue as a "feature request" as I can see, that the behaviour as is makes sense.
Still I hope in scenarios where a MethodTypeSpecifyingExtension uses $overwrite=true like I do with
return $this->typeSpecifier->create($methodCall->var, $reducedType, TypeSpecifierContext::createTrue(), true);
the ImpossibleCheckTypeHelper could be made a bit tolerant regarding the types involved.
as it seems, in the end phpstan and the type-system work as expected with my MethodTypeSpecifyingExtension but the "verification" after type changes is not happy with me changing the generic type involved.
I wanted to discuss my scenario before submitting failing test cases, to see whether we agree, that this is something usefull to support.