Doc-blocks for inferred return type of arrow functions

[alecwcp]

Since the body of arrow functions is a single statement, when psalm is unable to infer the return type there isn't an immediate place to put the annotation needed.

A contrived but demonstrating example is https://psalm.dev/r/926254686a

If the body of the function is made an assignment (since assignment returns the value too) an annotation can then be added that works, e.g.

$b = array_filter(
    $methodCalls,
    fn (string $methodCall): bool =>
        /** @var bool */
    	$dummy = $a->{$methodCall}
);

but this has forced us to introduce an unused variable.

This works because of the support documented here https://psalm.dev/docs/annotating_code/supported_annotations/ under "Off-label usage of the @var tag", specifically

If no VariableReference is given, the annotation tells Psalm that the right hand side of the expression, whether an assignment or a return, is of type Type.

Is it possible to expand on that (or another annotation?) to allow doing

$b = array_filter(
    $methodCalls,
    fn (string $methodCall): bool =>
        /** @var bool */
    	$a->{$methodCall}
);

and so removing the redundant variable?

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/926254686a

<?php
  
class A {
	public function __call(string $methodName, array $methodArguments)
    {
        if (substr($methodName, 0, 5) === 'isset') {
            return true;
        }
        return reset($methodArguments);
    }
}

$a = new A();

$methodCalls = ['isset1', 'isset2', 'isset3'];

$b = array_filter(
    $methodCalls,
    fn (string $methodCall): bool =>
    	$a->{$methodCall}
);

echo count($b);

Psalm output (using commit 5db75df):

INFO: MixedReturnStatement - 20:6 - Could not infer a return type

INFO: MixedInferredReturnType - 19:30 - Could not verify return type 'bool' for /var/www/vhosts/psalm.dev/httpdocs/src/somefile.php:19:334:-:closure

[alecwcp]

Sorry to comment on a closed issue but...

Just wanted to say that the response times of you guys are amazing 💯 🥇