Summary

When using array_filter with a callable annotated with @phpstan-assert-if-true, all keys in the resulting array were incorrectly marked as optional, even when the input elements already satisfied the asserted type. A callable with a conditional return type (@return ($value is Foo ? true : false)) correctly preserved keys as non-optional.

Changes

• Modified processKeyAndItemType() in src/Type/Php/ArrayFilterFunctionReturnTypeHelper.php to check the falsey branch when the boolean result is not definitely true
• If filterByFalseyValue makes the item or key variable type NeverType, the callback cannot return false for the given input type, so the key is not marked optional

Root cause

The processKeyAndItemType() method determined key optionality solely based on whether the callback's return type was definitely true ($booleanResult->isTrue()->yes()). For @phpstan-assert-if-true callbacks, the return type is bool (not conditionally true), so keys were always marked optional regardless of the input type.

The fix adds a secondary check: when the return type isn't definitely true, it evaluates the falsey branch. If filtering by the falsey value produces NeverType for the item or key variable, it means the false branch is impossible for this input type (e.g., passing Foo through a callback that asserts Foo on the true branch means the false branch would require !Foo, which is never). In that case, the key is correctly kept as non-optional.

Test

Added tests/PHPStan/Analyser/nsrt/bug-11730.php — an NSRT test that verifies array_filter with both a conditional return type callback and an @phpstan-assert-if-true callback produce array{Foo, Foo} (non-optional keys) when filtering an array of Foo elements.

Fixes phpstan/phpstan#11730