[Generics] Recursive / self-referencing template type variable

[teohhanhui]

Feature request

https://phpstan.org/r/ea622d5b-dd5f-47ba-a0e2-39a214c2d877

I understand that this would require #2928 first.

[teohhanhui]

I guess my use case in the code snippet is not really related to generics (as T is constant), but I just need a way to "declare" a type and re-use it in a recursive way? See phpstan/phpdoc-parser#9

But the feature request is still valid.

[muglug]

FYI recursive types are very hard to reason about (though support for a JSON recursive type would probably come in handy)

[phpstan-bot]

@teohhanhui PHPStan now reports different result with your code snippet:

@@ @@
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T|true> is not supported.
-16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, true>|true>|true>.
+16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, bool>|bool>|true>.

Full report

Line	Error
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
14	`PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T
16	`Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, bool>

[phpstan-bot]

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

@@ @@
+14: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
-14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T|true> is not supported.
-16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, true>|true>|true>.
+14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
+16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T|true> but returns array('a' => array('a1' => true, 'a2' => array('a2.1' => true)), 'b' => true).

Full report

Line	Error
14	Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
16	`Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T

[phpstan-bot]

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

@@ @@
+14: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
-14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T|true> is not supported.
-16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, true>|true>|true>.
+14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
+14: Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
+16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T|true> but returns array('a' => array('a1' => true, 'a2' => array('a2.1' => true)), 'b' => true).

Full report

Line	Error
14	Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
14	Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
16	`Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T

[phpstan-bot]

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

@@ @@
+14: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
-14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T|true> is not supported.
-16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, true>|true>|true>.
+14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
+14: Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
+16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T|true> but returns array{a: array{a1: true, a2: array{a2.1: true}}, b: true}.

Full report

Line	Error
14	Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type true is not supported.
14	Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
16	`Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T

[phpstan-bot]

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

@@ @@
+14: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
 14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
-14: PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() with bound type array<string, GraphQL\Type\Definition\T|true> is not supported.
-16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T but returns array<string, array<string, array<string, true>|true>|true>.
+14: Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
+16: Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T|true> but returns array{a: array{a1: true, a2: array{a2.1: true}}, b: true}.

Full report

Line	Error
14	Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid return type GraphQL\Type\Definition\T.
14	PHPDoc tag @template T for method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() has invalid bound type GraphQL\Type\Definition\T.
14	Template type T of method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() is not referenced in a parameter.
16	`Method GraphQL\Type\Definition\ResolveInfo::getFieldSelection() should return T of array<string, GraphQL\Type\Definition\T

[alexander-schranz]

I think I'm running into a similar issue with phpstan-type to produce recursive item: https://phpstan.org/r/5a1faff9-b45a-45c6-a9a0-9e29f5ec68d4

[ZebulanStanphill]

One notable use-case for recursive template types is an array-flattening method:

/**
 * Transforms multidimensional array to flat array. Based on Nette\Utils\Arrays::flatten().
 *
 * @template K of array-key
 * @template V of mixed
 *
 * @param array<K, V|array<K|V>> $array
 *
 * @return ($preserveKeys is true ? array<K, V> : list<V>)
 */
public static function flatten(array $array, bool $preserveKeys = false): array {
	// ...
}

[olleharstedt]

No progress here? I'm parsing an S-expression into a SplStack, and I'm not sure if there's a way to express such a type?

@return SplStack<string|SplStack<string|SplStack<string| ... etc