Contravariant bounds in generics

[dktapps]

Feature request

I have an event handler system where things that want to listen to an event can subscribe to it, by class.

This system also allows handlers to receive events which are of a subclass of the event they want to receive.

Closures already support contravariance on parameters, so I can implement this using bare closures, like this: https://phpstan.org/r/e59a6d1d-3bbd-411e-83ba-049a85782c9e
But I can't wrap the closures in objects, because generics don't support contravariant bounds: https://phpstan.org/r/d3180b26-22a2-44c0-83ce-01e757299b90

(These samples are entirely manufactured to make the point; the real system I need this for is implemented in PocketMine-MP since 2018 or so).

[phpstan-bot]

@dktapps PHPStan now reports different result with your code snippet:

@@ @@
-47: Parameter #2 $handlers of function callEvent expects array<EventHandler<SomeEventSubclass>>, array<EventHandler<SomeEvent>|EventHandler<SomeEventSubclass>> given.
+47: Parameter #2 $handlers of function callEvent expects array<EventHandler<SomeEvent>>, array<EventHandler<SomeEvent>|EventHandler<SomeEventSubclass>>&nonEmpty given.

Full report

Line	Error
47	`Parameter #2 $handlers of function callEvent expects array<EventHandler>, array<EventHandler

[phpstan-bot]

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

@@ @@
-No errors
+-1: Internal error: PHPStan\Rules\Methods\WrongCaseOfInheritedMethodRule::findMethod(): Argument #2 ($classReflection) must be of type PHPStan\Reflection\ClassReflection, null given, called in /var/task/vendor/phpstan/phpstan-strict-rules/src/Rules/Methods/WrongCaseOfInheritedMethodRule.php on line 40
+Run PHPStan with --debug option and post the stack trace to:
+https://github.com/phpstan/phpstan/issues/new?template=Bug_report.md

Full report

Line

Error

-1

Internal error: PHPStan\Rules\Methods\WrongCaseOfInheritedMethodRule::findMethod(): Argument #2 ($classReflection) must be of type PHPStan\Reflection\ClassReflection, null given, called in /var/task/vendor/phpstan/phpstan-strict-rules/src/Rules/Methods/WrongCaseOfInheritedMethodRule.php on line 40Run PHPStan with --debug option and post the stack trace to:https://github.com/phpstan/phpstan/issues/new?template=Bug_report.md

[phpstan-bot]

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

@@ @@
-47: Parameter #2 $handlers of function callEvent expects array<EventHandler<SomeEventSubclass>>, array<EventHandler<SomeEvent>|EventHandler<SomeEventSubclass>> given.
+-1: Internal error: PHPStan\Rules\Methods\WrongCaseOfInheritedMethodRule::findMethod(): Argument #2 ($classReflection) must be of type PHPStan\Reflection\ClassReflection, null given, called in /var/task/vendor/phpstan/phpstan-strict-rules/src/Rules/Methods/WrongCaseOfInheritedMethodRule.php on line 40
+Run PHPStan with --debug option and post the stack trace to:
+https://github.com/phpstan/phpstan/issues/new?template=Bug_report.md

Full report

Line

Error

-1

Internal error: PHPStan\Rules\Methods\WrongCaseOfInheritedMethodRule::findMethod(): Argument #2 ($classReflection) must be of type PHPStan\Reflection\ClassReflection, null given, called in /var/task/vendor/phpstan/phpstan-strict-rules/src/Rules/Methods/WrongCaseOfInheritedMethodRule.php on line 40Run PHPStan with --debug option and post the stack trace to:https://github.com/phpstan/phpstan/issues/new?template=Bug_report.md

[phpstan-bot]

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

@@ @@
-47: Parameter #2 $handlers of function callEvent expects array<EventHandler<SomeEventSubclass>>, array<EventHandler<SomeEvent>|EventHandler<SomeEventSubclass>> given.
+47: Parameter #2 $handlers of function callEvent expects array<EventHandler<SomeEvent>>, non-empty-array<EventHandler<SomeEvent>|EventHandler<SomeEventSubclass>> given.

Full report

Line	Error
47	`Parameter #2 $handlers of function callEvent expects array<EventHandler>, non-empty-array<EventHandler

[ondrejmirtes]

Here's how to implement it: #7502 (comment)

[github-actions]

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