Allow passing methods with arguments to extensionMethod

[jtojnar]

Since 01863f2 introduced callable(static): mixed type hint for the extensionMethod parameter, it is no longer possible to pass functions with more than one argument to it.

This is because argument of type callable(static): mixed only has a limited number of subtypes: functions that can be called with the static argument, i.e. those functions expecting any superclass of static. The functions can also narrow down as they want since the return type since mixed is supertype of every type. The functions cannot have any extra arguments since the container would not know what to pass to them. But having fewer arguments is fine since PHP will ignore any extra arguments passed to a function.

Formally, the subtyping relation of callables must respect the variance rules.

If we want to allow wider range of subtypes, we must choose a suitably wide supertype in the type lattice. One option would be just using mixed or callable but those do not really guide user very well. We want to include at least the static argument since that is always passed by __call.

One option would be using a bottom type (never) as the parameter type since it is a subtype of any type – the function with never argument can never be called so substituting it with a function that accepts a supertype cannot break any callers, satisfying the contravariance rule. For the return type, we can use a top type (mixed) since callers expecting mixed must be able to deal with narrower types so functions returning a subtype cannot break anything either, thus covariance of return type. The main limitation is that we can only have as many arguments as we specify in the type signature as mentioned above. I chose 9 extra arguments since that should be enough for most uses.

Though, since the function with never argument cannot be called because there are no values that can inhabit never type, and thus there is nothing to be passed to arguments, we need to cast down the arguments in __call to never types. This is a valid operation since never is a subtype of any type but it is a bit weird.

• bug fix
• BC break? no
• doc PR: N/A

[JanTvrdik]

Have you tried callable(static, ...never): mixed instead?

[jtojnar]

Oh, good idea. Unfortunately, that does not seem to work with PHPStan 2.2.5:

Parameter #2 $callback of static method Nette\Forms\Container::extensionMethod() expects callable(static, never ...): mixed,     
         Closure(Nette\Forms\Container, string, callable, int=, bool=): static given.

https://phpstan.org/r/86e4483a-24eb-41e2-afc8-ed3c5c5ba899