Fix phpstan/phpstan#9634: Cannot use "T is never" in conditional return

[phpstan-bot]

Summary

When using (T is never ? false : bool) as a conditional return type on a generic interface method, PHPStan incorrectly reported "Condition 'T is never' in conditional return type is always false." The fix allows never to correctly recognize that a template type T might be instantiated to never.

Changes

• Added TemplateType handling in src/Type/NonAcceptingNeverType.php — isSuperTypeOf() now returns Maybe for template types instead of No
• Added the same TemplateType handling in src/Type/NeverType.php for consistency
• New rule test in tests/PHPStan/Rules/PhpDoc/data/bug-9634.php and test method in tests/PHPStan/Rules/PhpDoc/MethodConditionalReturnTypeRuleTest.php
• New type inference test in tests/PHPStan/Analyser/nsrt/bug-9634.php verifying that Option<never>::isSome() resolves to false and Option<int>::isSome() resolves to bool

Root cause

NonAcceptingNeverType::isSuperTypeOf() (the type used for explicitly written never in PHPDoc) returned No for all types except NeverType and NonAcceptingNeverType. When ConditionalReturnTypeRuleHelper checked whether the condition T is never could ever be true by calling $targetType->isSuperTypeOf($subjectType), the never target returned No for the template type T, causing the rule to report the condition as "always false". However, a template type T can be instantiated to never (since never is a subtype of any bound), so the correct answer is Maybe.

Test

• Rule test verifies that (T is never ? false : bool) no longer produces a false positive error
• NSRT test verifies that when T is bound to never, the conditional resolves to false, and when T is bound to int, it resolves to bool

Fixes phpstan/phpstan#9634
Fixes phpstan/phpstan#10938

[VincentLanglet]

• Add test for the issue phpstan/phpstan#10938
• Use nsrt/bug-9634 file in testBug9634 and delete the duplicate
• Be sure both NeverType and NonAcceptingNeverType are necessary/tested

[phpstan-bot]

All three review points have been addressed:

1. Use nsrt/bug-9634 in testBug9634 and delete the duplicate - The rule test now references tests/PHPStan/Analyser/nsrt/bug-9634.php and the duplicate tests/PHPStan/Rules/PhpDoc/data/bug-9634.php has been deleted.

2. Add test for issue #10938 - Created tests/PHPStan/Analyser/nsrt/bug-10938.php which tests a Collection interface with (TValue is never ? true : bool) conditional return type, and added testBug10938() in MethodConditionalReturnTypeRuleTest.

3. Ensure both NeverType and NonAcceptingNeverType are necessary/tested - Added 4 test cases in TemplateTypeTest::dataIsSuperTypeOf that explicitly verify both NeverType::isSuperTypeOf(TemplateType) and NonAcceptingNeverType::isSuperTypeOf(TemplateType) return Maybe (with both unbound and bounded template types). Both changes are necessary: NonAcceptingNeverType overrides isSuperTypeOf completely and doesn't call the parent, so each class needs its own TemplateType check.

All tests pass (make tests: 11679 tests, 0 failures) and make phpstan reports no errors.