Allow calling methods by a literal string variable

[danog]

https://psalm.dev/r/501d719ba6

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/501d719ba6

<?php
class a {
    public static function a(): int { return 0; }
	public static function b(): string { return "test"; }
}

$c = random_int(0, 1) ? 'a' : 'b';
/** @psalm-trace $c */;
$c = a::$c();
/** @psalm-trace $c */;

Psalm output (using commit 028ac7f):

INFO: Trace - 8:23 - $c: 'a'|'b'

INFO: MixedAssignment - 9:1 - Unable to determine the type that $c is being assigned to

INFO: Trace - 10:23 - $c: mixed

INFO: UnusedVariable - 9:1 - $c is never referenced or the value is not used

[orklah]

I'm quite surprised it doesn't work. It's not even an issue with the 'a'|'b' thing. Even with 'a' it fails. It shouldn't be difficult as I think something close to that must be already working for callable-arrays resolution

[AndrolGenhald]

Related: #5743 (comment)

We don't currently resolve literal strings to callables: https://psalm.dev/r/13a7a514f3. Not sure if that's an intentional choice or not.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/13a7a514f3

<?php

$callable = "is_array";
$test = $callable([]);
/** @psalm-trace $test */;

Psalm output (using commit 028ac7f):

INFO: MixedAssignment - 4:1 - Unable to determine the type that $test is being assigned to

INFO: Trace - 5:26 - $test: mixed

INFO: UnusedVariable - 4:1 - $test is never referenced or the value is not used

[orklah]

I don't think this was intentional, more like a nice to have feature that never made it.

Now that we had an RFC to declare what we can and can't do with callable-arrays, it makes even more sense to support all that is still relevant