Type of ReflectionEnum::getBackingType() should/could be narrowed after ::isBacked()

[RobertMe]

Bug report

The formal return value of ReflectionEnum::getBackingType() is ?ReflectionNamedType. But it will always return ReflectionNamedType (i.e.: be non-null) for backed enums. So when a ReflectionEnum::isBacked condition is applied the type could/should be narrowed.

Code snippet that reproduces the problem

https://phpstan.org/r/6708f7db-5547-47c6-aa37-38dc5974a1a4

Expected output

Type could/should be just ReflectionNamedType (but is ReflectionNamedType|null).

Did PHPStan help you today? Did it make you happy in any way?

No response

[ondrejmirtes]

Alternatively you can write this more SA-friendly code https://phpstan.org/r/03d3e5a0-4820-4c4f-a481-c728f6f14735

[RobertMe]

I think this would be a relatively simple issue which I might fix myself given some pointers. I think it might even be possible to implement it using simple assertions in a stub file?

Based on narrowing types (especially the hasName / getName example) I think it should be possible to write a stubs/ReflectionEnum.stub (and add it to the stubFiles in `config/config.neon). This could then just contain:

<?php

class ReflectionEnum
{
    /**
     * @phpstan-assert-if-true !null $this->getBackingType()
     */
    public function isBacked()
    {
    }
}

Correct? I'll then just need some pointers on testing the stub

[RobertMe]

Alternatively you can write this more SA-friendly code https://phpstan.org/r/03d3e5a0-4820-4c4f-a481-c728f6f14735

First off, wow, that reply was way quicker then I expected 😃. Secondly, you're right, not sure why I didn't think of that. But still would be nice if PHPStan automatically narrowed the type 😅. And might be a good "first issue" for myself to learn more about PHPStan "internals".

[ondrejmirtes]

Yeah, sure, should be easy. Just check how I tested the return type of getCase/getCases around the same commit ReflectionEnum stub was added.

Hint: in NodeScopeResolverTest

[franmomu]

Would be possible to also narrow the template type to BackedEnum (after calling isBacked())? that way $reflectionEnum->getName() would be class-string<BackedEnum> I guess.

https://phpstan.org/r/63e742a3-f3b7-4d5a-9c6e-3a60de5bfa32

Update: Just saw #10192 (comment)

[phpstan-bot]

@franmomu After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
 ==========
 
 6: Dumped type: class-string<UnitEnum>
-8: Dumped type: class-string<UnitEnum>
+8: Dumped type: class-string<BackedEnum>
 
 PHP 7.2 – 8.0 (7 errors)
 ==========

Full report

PHP 8.1 – 8.3 (2 errors)

Line	Error
6	Dumped type: class-string<UnitEnum>
8	Dumped type: class-string<BackedEnum>

PHP 7.2 – 8.0 (7 errors)

Line	Error
4	Parameter $class of function test() has invalid type UnitEnum.
5	Instantiated class ReflectionEnum not found.
6	Call to method getName() on an unknown class ReflectionEnum.
6	Dumped type: *ERROR*
7	Call to method isBacked() on an unknown class ReflectionEnum.
8	Call to method getName() on an unknown class ReflectionEnum.
8	Dumped type: *ERROR*

[ondrejmirtes]

Fixed phpstan/phpstan-src#2830

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