Fix intersection in generics

[VincentLanglet]

Without the fix I get

------ ----------------------------------------------------------------------------------------------------------------------------------------------------- 
  Line   bug-5336.php                                                                                                                                         
 ------ ----------------------------------------------------------------------------------------------------------------------------------------------------- 
  23     Property Bug5336\Pager::$query is never read, only written.                                                                                          
  50     Property Bug5336\Test::$pager (Bug5336\Pager<Bug5336\ProxyQueryInterface&Bug5336\Stub>) does not accept Bug5336\Pager<Bug5336\ProxyQueryInterface>.  
  51     Expected type Bug5336\Pager<Bug5336\ProxyQueryInterface&Bug5336\Stub>, actual: Bug5336\Pager<Bug5336\ProxyQueryInterface>                            
 ------ ----------------------------------------------------------------------------------------------------------------------------------------------------- 

on the file.

With the fix I get

------ ------------------------------------------------------------- 
  Line   bug-5336.php                                                 
 ------ ------------------------------------------------------------- 
  23     Property Bug5336\Pager::$query is never read, only written.  
 ------ ------------------------------------------------------------- 

The fix I made in IntersectionType::inferTemplateTypesOn might be improved...
More important, I don't know if the fix should be added to IntersectionType::inferTemplateTypes too (and what's the diff between both methods).

Close phpstan/phpstan#5336

[VincentLanglet]

I rebased on master @ondrejmirtes :)

[VincentLanglet]

Friendly ping @ondrejmirtes

[ondrejmirtes]

Hi, I don't feel like this fix is right, the $inferred->isEmpty() condition is weird and I don't know how it's justified. But for me I'd have to think long and hard about this and it's not in my current priorities. Thanks for understanding.

[VincentLanglet]

Hi, I don't feel like this fix is right, the $inferred->isEmpty() condition is weird and I don't know how it's justified.

There is an intersection type

Bug5336\ProxyQueryInterface & Bug5336\Stub

on which the call

inferTemplateTypesOn

is made with

T of Bug5336\ProxyQueryInterface (class Bug5336\Pager, parameter)

This call is doing

$templateType->inferTemplateTypes($type)

on each type of the intersection.

Then

(T of Bug5336\ProxyQueryInterface)->inferTemplateTypes(Bug5336\ProxyQueryInterface) 

is Bug5336\ProxyQueryInterface, but

(T of Bug5336\ProxyQueryInterface)->inferTemplateTypes(Bug5336\Stub) 

Is empty

This is the empty check I do. In order to add again the type Bug5336\Stub.
When a type has nothing in common with the template type, it just need to be fully keep as an extra condition.

[arnaud-lb]

@VincentLanglet this is what I'm seeing as well: The intersection members that are not a sub type of the template bound are rejected by T->inferTemplateTypes(), so we end up with just ProxyQueryInterface.

I agree that it would be useful to not reject the extra types.

I can see the following issues with the current fix:

• I think that there are cases where isEmpty() will not be enough to detect this. I was not able to find a case demonstrating that, though.
• If the intersection does not contain any compatible type, it may result in invalid type inference: https://phpstan.org/r/babfd6ef-222c-4ff5-bd97-7f3d2ec02ef6
• It doesn't handle nested template types: https://phpstan.org/r/15e4e15e-0999-409c-ba64-8728468c2cce

[ondrejmirtes]

To me it also looked like the current logic in this PR isn't sufficient, thanks.

[VincentLanglet]

To me it also looked like the current logic in this PR isn't sufficient, thanks.

No problem.

I can see the following issues with the current fix:

I think that there are cases where isEmpty() will not be enough to detect this. I was not able to find a case demonstrating that, though.
If the intersection does not contain any compatible type, it may result in invalid type inference: https://phpstan.org/r/babfd6ef-222c-4ff5-bd97-7f3d2ec02ef6
It doesn't handle nested template types: https://phpstan.org/r/15e4e15e-0999-409c-ba64-8728468c2cce

Any idea what would be the right fix @arnaud-lb ?