Hey

We've found use cases for deferring field resolution directly, without parameters or prefetch, e.g.:

#[Type]
class SomeType {
    #[Field(outputType: 'Int!')]
    public function complexCalculation(
        bool $arg1
    ): Deferred {
        // Do something with $arg1, similar to prefetch

        // Return value from some kind of buffer, again, similar to prefetch
        return new Deferred(fn () => 123);
    }
}

Currently it's possible, but ugly:

• requires the use of outputType
• forces the return type to be GraphQL\Deferred
• forces creation of new GraphQL\Deferred instance everywhere

I propose that such cases are simplified into returning a (typed) callable, which removes the dependency on Deferred from userland code, as well as allows specifying an actual PHPDoc type:

#[Type]
class SomeType {
    /** @return callable(): int */
    #[Field]
    public function complexCalculation(
        bool $arg1
    ): callable {
        // Do something with $arg1, similar to prefetch

        // Return value from some kind of buffer, again, similar to prefetch
        return fn () => 123;
    }
}

The implementation should be somewhat trivial - under the hood the callable value would just get wrapped in Deferred, and additional root type mapper would handle callable() PHPDoc types. Thoughts?