A way to use signature of another method as a type

[weirdan]

Rationale

Some methods may have signatures based on other methods. One particular example is Laravel's Dispatchable trait, where methods have signatures based on constructor signature.

It would be great if we had a way to specify something like this:

<?php declare(strict_types=1);

trait Creatable 
{
   /** @param method-args<static::__construct> $args */
   public static function create(...$args): static
   {
      return new static(...$args);
   }
   
   /** @param method-args<static::__construct> $args */
   public static function createIf(bool $condition, ...$args): static|null
   {
      return $condition ? new static(...$args) : null;
   }
}

final class A
{
   use Creatable;
   public function __construct(private int $param) {}
}

final class B
{
   use Creatable; 
   public function __construct(private string $param) {}
}

$a = A::create(2); // valid
$b = B::createIf(true === true, "42"); // valid

$aa = A::createIf(true, "42"); // invalid
$bb = B::create(2); // invalid

https://psalm.dev/r/bd50e7e47e

Prior art

Parameters<T>, ConstructorParameters<T> and ReturnType<T> in Typescript.

Typescript, however, builds those types on function signature types + generics + infer: https://github.com/microsoft/TypeScript/blob/a3092c798ad9f165b0f7cba964a2c7b976cd30d0/lib/lib.es5.d.ts#L1601

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/bd50e7e47e

<?php

trait Creatable 
{
   /** @param method-args<static::__construct> $args */
   public static function create(...$args): static
   {
      return new static(...$args);
   }
   
   /** @param method-args<static::__construct> $args */
   public static function createIf(bool $condition, ...$args): static|null
   {
      return $condition ? new static(...$args) : null;
   }
}

final class A
{
   use Creatable;
   public function __construct(private int $param) {}
}

final class B
{
   use Creatable; 
   public function __construct(private string $param) {}
}

$a = A::create(2); // valid
$b = B::createIf(true === true, "42"); // valid

$aa = A::createIf(true, "42"); // invalid
$bb = B::create(2); // invalid

Psalm output (using commit 12f33fa):

ERROR: InvalidArgument - 30:16 - Argument 1 of A::create expects method-args<A::__construct>, but 2 provided

ERROR: InvalidArgument - 31:33 - Argument 2 of B::createIf expects method-args<B::__construct>, but '42' provided

ERROR: InvalidArgument - 33:25 - Argument 2 of A::createIf expects method-args<A::__construct>, but '42' provided

ERROR: InvalidArgument - 34:17 - Argument 1 of B::create expects method-args<B::__construct>, but 2 provided

INFO: UnusedVariable - 30:1 - $a is never referenced or the value is not used

INFO: UnusedVariable - 31:1 - $b is never referenced or the value is not used

INFO: UnusedVariable - 33:1 - $aa is never referenced or the value is not used

INFO: UnusedVariable - 34:1 - $bb is never referenced or the value is not used

ERROR: UndefinedDocblockClass - 5:15 - Docblock-defined class, interface or enum named method-args does not exist

ERROR: UndefinedConstant - 5:15 - Constant A::__construct is not defined

INFO: MixedInferredReturnType - 6:45 - Could not verify return type 'A' for Creatable::create

ERROR: UndefinedDocblockClass - 11:15 - Docblock-defined class, interface or enum named method-args does not exist

ERROR: UndefinedConstant - 11:15 - Constant A::__construct is not defined

INFO: MixedInferredReturnType - 12:64 - Could not verify return type 'A|null' for Creatable::createIf

ERROR: UndefinedConstant - 5:15 - Constant B::__construct is not defined

INFO: MixedInferredReturnType - 6:45 - Could not verify return type 'B' for Creatable::create

ERROR: UndefinedConstant - 11:15 - Constant B::__construct is not defined

INFO: MixedInferredReturnType - 12:64 - Could not verify return type 'B|null' for Creatable::createIf

[weirdan]

Could be extended to functions and callable, and include return types:

/**
 * @param function-args<$func> $args
 * @return function-return<$func>
 */
function call_user_func(callable $func, ...$args) { ... }