Fix phpstan/phpstan#9045: Narrowed template on an interface is ignored when generics is not specified

[phpstan-bot]

Summary

When a child interface narrows a template bound and passes it to a parent interface via @extends, using the child without explicit generic parameters incorrectly resolved the template to the parent's wider bound instead of the child's narrowed bound.

For example:

/** @template T of TranslationInterface */
interface TranslatableInterface {
    /** @return T */
    public function getTranslation(): TranslationInterface;
}

/** @template T of TransportTranslationInterface @extends TranslatableInterface<T> */
interface TransportInterface extends TranslatableInterface {}

// $transport->getTranslation() was incorrectly typed as TranslationInterface
// instead of TransportTranslationInterface
function foo(TransportInterface $transport): void {
    $transport->getTranslation(); // should be TransportTranslationInterface
}

Changes

• Added getActiveTemplateTypeMapForAncestorResolution() method in src/Reflection/ClassReflection.php that resolves ErrorType entries to their template bounds, but only when the bound is not mixed. This preserves the existing behavior for mixed-bounded templates (like Iterator<TKey>) while correctly resolving narrowed bounds.
• Updated getImmediateInterfaces() and getParentClass() in ClassReflection to use this new method when resolving @extends and @implements type declarations
• Updated tests/PHPStan/Analyser/nsrt/bug-2676.php: Collection's TKey of array-key now correctly resolves to (int|string) instead of mixed when not explicitly specified

Root cause

When a plain ObjectType (without generics) referred to a generic class, ObjectType::getClassReflection() created a ClassReflection with all template types set to ErrorType. In getImmediateInterfaces(), when resolving @extends TranslatableInterface<T>, the ErrorType for T was propagated to the parent, where it was resolved using the parent's own (wider) template bound (TranslationInterface) instead of the child's narrower bound (TransportTranslationInterface).

The fix intercepts this propagation: before passing template types to ancestor resolution, ErrorType entries with non-mixed bounds are resolved to their template bounds. This ensures the narrowed bound is correctly propagated through the inheritance chain.

Test

Added tests/PHPStan/Analyser/nsrt/bug-9045.php that verifies TransportInterface::getTranslation() correctly returns TransportTranslationInterface when the interface is used without explicit generic parameters.

Fixes phpstan/phpstan#9045
Fixes phpstan/phpstan#7185
Fixes phpstan/phpstan#13204

[staabm]

add a regression test for

• phpstan/phpstan#7185
• phpstan/phpstan#13204

[phpstan-bot]

Done. Added regression tests for both issues:

• tests/PHPStan/Analyser/nsrt/bug-7185.php — Tests that iterator_to_array() on a Collection (extending IteratorAggregate<TKey, TValue of object>) without explicit generics correctly resolves values as object instead of mixed.

• tests/PHPStan/Analyser/nsrt/bug-13204.php — Tests that instanceof ParentNode (extending ArrayAccess<int, TChild|null> with TChild of object) correctly resolves offset access as object|null instead of mixed.

Both tests pass, and the full test suite (11691 tests) and phpstan analysis are clean.

[staabm]

thank you!