Incorrect expected return type with union type and generic

[tjveldhuizen]

Bug report

When I use this combination of generics and union types, PHPStan reports an error falsely.

Code snippet that reproduces the problem

https://phpstan.org/r/a630ff19-a6d5-4b16-b677-1c543bce7310

Expected output

No error expected

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

PHPStan absolutely helps us to have more trust in changes to our legacy codebase, which still needs a lot of tests.

[arnaud-lb]

Shorter snippet: https://phpstan.org/r/73ff0bed-e705-4c3f-9f5d-18f03f934fb7

Appears to be caused by https://github.com/phpstan/phpstan-src/blob/f8c1bef517be0777cc2897b893bfcae97cbd254e/src/Type/TypeCombinator.php#L79-L81

The problem is that the TemplateBooleanType gets replaced by a BooleanType here because TemplateBooleanType is an instance of BooleanType.

One solution could be to move the implementation of TypeCombinator::remove() to Type, so that template types could implement their own logic. WDYT @ondrejmirtes ?

[ondrejmirtes]

Yeah, moving things to the Type interface always cleans stuff up, I'm for it :)

[phpstan-bot]

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

@@ @@
-PHP 8.0 – 8.1 (1 error)
+PHP 8.0 – 8.1 (2 errors)
 ==========
 
+10: PHPDoc tag @param for parameter $value with type T of bool|int is not subtype of native type bool|int.
 16: Method HelloWorld::getValueDescription() should return array{value: T of bool|int, description: string}|null but returns array{value: int|true, description: string}.
 
-PHP 7.1 – 7.4 (2 errors)
+PHP 7.1 – 7.4 (3 errors)
 ==========
 
 10: Method HelloWorld::getValueDescription() uses native union types but they're supported only on PHP 8.0 and later.
+10: PHPDoc tag @param for parameter $value with type T of bool|int is not subtype of native type bool|int.
 16: Method HelloWorld::getValueDescription() should return array{value: T of bool|int, description: string}|null but returns array{value: int|true, description: string}.

Full report

PHP 8.0 – 8.1 (2 errors)

Line	Error
10	`PHPDoc tag @param for parameter $value with type T of bool
16	`Method HelloWorld::getValueDescription() should return array{value: T of bool

PHP 7.1 – 7.4 (3 errors)

Line	Error
10	Method HelloWorld::getValueDescription() uses native union types but they're supported only on PHP 8.0 and later.
10	`PHPDoc tag @param for parameter $value with type T of bool
16	`Method HelloWorld::getValueDescription() should return array{value: T of bool

[github-actions]

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