Wrong type inference when using array_map and Generics

[b-viguier]

Bug report

I'm playing a lot with Generics and I encountered a strange issue. I reproduced the issue with a minimal code. The goal is to wrap a value of Generic type in a wrapper class. When I want to unwrap a list of wrapped values, I use array_map, but when I try to wrap again this array I'm facing different results according to the used method.

Code snippet that reproduces the problem

https://phpstan.org/r/09243518-e539-4a98-8a24-4400d2d766a6

Expected output

The snippet contains two versions of the same function. PhpStan complains about unwrapAllAndWrapAgain but not about unwrapAllAndWrapAgain2. It's like the type narrowing fails, and then we have to compare a mixed type 🤨

🙇‍♂️Thanks a lot for your amazing work on PhpStan, it's really a game changer in Php ecosystem 👏

[ondrejmirtes]

Hi, neither unwrapAllAndWrapAgain nor unwrapAll actually work, see: https://phpstan.org/r/dba21179-2463-4e08-bc9e-5b717dad5bbd

If you use a closure instead of a string argument, it all works: https://phpstan.org/r/f7ee5f7e-87c2-4efa-a1b2-867604694bbf

I don't think we can solve it in a nice way right now. The problem is that "function as a string" is supported through PHPStan\Type\Type::getCallableParametersAcceptors() which returns ParametersAcceptor[], but the template type map is on FunctionReflection/MethodReflection, one level up.

[ondrejmirtes]

And thank you for your kind words! :)

[b-viguier]

Thanks for this fast and helpful reply 👍
Executable strings are always tedious to handle 😉 I had the same result with a callable array (i.e [$this, 'unwrap']), I imagine both cases are related.

For your information, I tested with an arrow function, I expected the same behavior than with a classic anonymous function, but it still produces the same error… Are arrow functions treated differently from normal closures? 🤔
https://phpstan.org/r/c75198c5-506f-4026-9ec0-93c7886ff818

By the way, I didn't know the \PHPStan\dumpType function, it will be very helpful to understand how type are inferred with Generics 👍

Since this behavior is a known limitation, we can close this issue from my point of view.
🙇‍♂️

[ondrejmirtes]

The thing is - PHPStan mostly understands executable strings and callable arrays, it just doesn't work for generics in this case :)

Arrow functions are different from closures in some key areas so inferring the return type from the function body is not yet implemented, see: #3660

I'm gonna keep this open, it's always possible it will start working thanks to some internal change, or I get an idea how to implement it effortlessly :)

Thanks.

[phpstan-bot]

@b-viguier After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-PHP 7.4 – 8.0 (5 errors)
+PHP 7.4 – 8.0 (4 errors)
 ==========
 
 50: Dumped type: Closure(Wrapper): mixed
 51: Dumped type: Closure(Wrapper): mixed
 53: Dumped type: array<int, T-all (function unwrapAllAndWrapAgain(), argument)>
-56: Dumped type: array<int, mixed>
-58: Function unwrapAllAndWrapAgain() should return Wrapper<array<int, T-all>> but returns Wrapper<array<int, mixed>>.
+56: Dumped type: array<int, T-all (function unwrapAllAndWrapAgain(), argument)>
 
 PHP 7.1 – 7.3 (5 errors)
 ==========

Full report

PHP 7.4 – 8.0 (4 errors)

Line	Error
50	Dumped type: Closure(Wrapper): mixed
51	Dumped type: Closure(Wrapper): mixed
53	Dumped type: array<int, T-all (function unwrapAllAndWrapAgain(), argument)>
56	Dumped type: array<int, T-all (function unwrapAllAndWrapAgain(), argument)>

PHP 7.1 – 7.3 (5 errors)

Line	Error
49	Syntax error, unexpected T_VARIABLE, expecting ')' on line 49
56	Syntax error, unexpected ',' on line 56
56	Syntax error, unexpected T_VARIABLE, expecting ')' on line 56
58	Syntax error, unexpected ',' on line 58
58	Syntax error, unexpected T_VARIABLE, expecting ')' on line 58

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.