First Class Callable: Catch UndefinedMethod

[jarstelfox]

https://psalm.dev/r/b6bb608bf8

This syntax under the hood uses Closure::fromCallable, which will bind to the current scope. It seems like we should be able to statically answer if a method/class would be undefined.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b6bb608bf8

<?php

class FuncLib {
    public static function MyFunc(): void {
        echo "MyFunc";
    }
}
class A {
    /** @var Closure */
    public $callbackWillWork;
    
    /** @var Closure */
    public $callbackBroken;
    
    public function __construct() {
       $this->callbackWillWork = FuncLib::MyFunc(...);
       $this->callbackBroken = FuncLib::DOES_NOT_EXIST(...);
    }
}

Psalm output (using commit 77650e7):

No issues!