Intersections appear not to be templated properly

[muglug]

Code snippet that reproduces the problem

class MockObject
{
	public function checkExpectations() : void
	{
	}
}

/**
 * @template RequestedType
 * @param class-string<RequestedType> $className
 * @return RequestedType&MockObject
 */
function mock(string $className)
{
	$instance = eval("there be dragons");

	return $instance;
}

class A {
	public function foo() : void {}
}

/**
 * @template UnknownType
 * @param class-string<UnknownType> $className
 */
function useMockTemplated(string $className) : void
{
	mock($className)->checkExpectations();
}

mock(A::class)->foo(); // good
mock(A::class)->checkExpectations(); // good
mock(A::class)->notFoo(); // bad

Expected output

Method (A&MockObject)::notFoo does not exist

Actual output

No issues

[ondrejmirtes]

PHPStan is confused because you're creating intersection from two classes. If you make MockObject an interface, it works: https://phpstan.org/r/9149e4de-55cc-45e5-a1ac-13d6bdd9d750

Your playground link (missing from the description): https://phpstan.org/r/10bd4532-0406-4a64-a82c-5f317372fa7c

There should probably be a rule that checks if the final return type after inferring types isn't NeverType...

[arnaud-lb]

What is happening here is that RequestedType is being resolved to A, however the type A&MockObject is impossible (they are unrealated classes). In the type system, this results in a "never type" or "error type", which is usually spotted later by rules and reported as an error.

[ondrejmirtes]

It’s not spotted in this case because the NeverType rule is called on method declaration but here it happens in a specific method call.

[phpstan-bot]

@ondrejmirtes After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-No errors
+26: Return type of call to function mock contains unresolvable type.
+27: Return type of call to function mock contains unresolvable type.
+28: Return type of call to function mock contains unresolvable type.

Full report

Line	Error
26	Return type of call to function mock contains unresolvable type.
27	Return type of call to function mock contains unresolvable type.
28	Return type of call to function mock contains unresolvable type.

[ondrejmirtes]

Implemented: phpstan/phpstan-src@58c29fd

[github-actions]

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