Template without common ancestor

[jornane]

https://psalm.dev/r/9d4c7819b6

When using @template T in a function, Psalm assumes that there is a common ancestor for T, but this may not be the case, for example when array<T> is used.

In the example, a parameter to the function is array<class-string<T>,callable(T):string>,
meaning a class and a function that takes an object of this class to convert it to a string. T may for example be DateTime or DateInterval, these have no common ancestor.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/5a52410f7d

<?php
/**
 * @template T
 *
 * @param array<object> $data
 * @param array<class-string<T>,callable(T):string> $transform
 * @return array<object|string>
 */
function transform( array $data, array $transform = [] ): array {
	foreach( $data as $key => $value ) {
		foreach( $transform as $class => $transformer ) {
			if ( is_a( $value, $class ) ) {
				$data[$key] = $transformer( $value );
			}
		}
	}
	return $data;
}

class A {
	public function __construct(public readonly string $aValue) {}
}
class B {
	public function __construct(public readonly string $bValue) {}
}

var_export(transform(
	[new A('A'), new B('B')],
	[
		A::class => fn(A $a) => $a->aValue,
		B::class => fn(B $b) => $b->bValue,
	]
));

Psalm output (using commit 20a21f9):

ERROR: InvalidArgument - 27:12 - Type B should be a subtype of A