Template of callable arguments

[mathroc]

Feature request

When wrapping callable, we might want to describe that the callable we return will take the same arguments that the one we got as an argument. (see phpstan/phpstan#6813 for a short discussion on the subject)

Here is an exemple of what the syntax could look like:

https://psalm.dev/r/4e9c0e1d18

I like that it feels right to "expand" the array of types with callable(...A), but I know it might be confusing given callable(A...) as a different meaning

---

some other use cases for this feature:

/**
 * @template A1
 * @template Arest of array<mixed>
 * @template R
 * @param callable(A1, ...Arest): R
 * @return callable(...Arest): R
 */
function curry(callable $f, mixed $arg1): callable {
  return static fn (...$args) => $f($arg1, ...$args);
}

/**
 * @template A of array<mixed>
 * @template Rf
 * @template Rg
 * @param callable(...A): Rf $f
 * @param callable(Rf): Rg $g
 * @return callable(...A): Rg
function combine(callable $f, callable $g): callable {
   return static fn (...$args) => $g($f(...$args));
}

---

copied from phpstan/phpstan#6873

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/4e9c0e1d18

<?php declare(strict_types = 1);

/**
 * @template A of array<mixed>
 * @param \Closure(...A): int $f
 * @return \Closure(...A): string
 */
function castToStringWrapper(\Closure $f): \Closure {
	return static fn (...$args): mixed => (string) $f(...$args);
}

$myRandomStringInt = castToStringWrapper(random_int(...));

Psalm output (using commit 16b24bd):

ERROR: InvalidArgument - 12:42 - Argument 1 of castToStringWrapper expects Closure(array<array-key, mixed>...):int, but pure-Closure(int, int):int provided

INFO: UnusedVariable - 12:1 - $myRandomStringInt is never referenced or the value is not used