test+docs: error-side exhaustiveness for enum and sealed error types#86
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Code Review
This pull request adds type-level tests to tests/Types/result.php to verify and document error exhaustiveness behavior under PHPStan. It demonstrates that checking isErr() preserves specific types for native enums and @phpstan-sealed union interfaces, while documenting a known limitation where using instanceof Err loses the error type, resulting in mixed. There are no review comments, so I have no feedback to provide.
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Walkthrough
Changesエラー型網羅性テスト
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Actionable comments posted: 1
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Inline comments:
In `@tests/Types/result.php`:
- Around line 420-430: The test function testInstanceofErrLosesErrorType only
validates the instanceof Err type loss with the enum variant Result<int,
HttpError>, but the docstring claims this behavior occurs for both enum and
sealed classes. Add a complementary test function that validates the same type
loss behavior using the sealed class variant Result<int, AppError> to ensure
test coverage aligns with the documented behavior and improves edge case
regression detection for both type variants.
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tests/Types/result.php
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Pull request overview
This PR pins (via PHPStan assertType fixtures) that Result<T, E> preserves error-side type information well enough to allow exhaustive matching when E is a native enum or a @phpstan-sealed union, and documents the recommended narrowing/extraction patterns in the README.
Changes:
- Added new type fixtures validating exhaustive
matchbehavior forenumand@phpstan-sealederror types. - Added fixtures demonstrating the known pitfall where
instanceof ErrdropsEtomixed. - Documented “Exhaustive error matching” guidance in the Type Safety section of the README.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| tests/Types/result.php | Adds enum/sealed-union error fixtures and PHPStan assertType checks to pin exhaustive matching behavior and the instanceof Err pitfall. |
| README.md | Documents exhaustive error matching guidance and recommended extraction/narrowing patterns. |
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概要
エラー型（
Result<T, E>のE）が native enum /@phpstan-sealedunion の場合、エラー値を網羅的に分岐できることを assertType 型テストでピン留めし、README にも明記しました。テスト（
tests/Types/result.php）フィクスチャ:
HttpError(enum),AppError(@phpstan-sealed)・ValidationFailure/NetworkFailuretestEnumErrorExhaustivenessisErr()経由ならunwrapErr()が enum 型を保ち、全ケースのmatch（default なし）が網羅と認識されるtestSealedErrorExhaustivenessmatch(true)+instanceofが網羅と認識される（エラークラスは非ジェネリックなので型引数喪失なし）testInstanceofErrLosesErrorTypeinstanceof Errでは E が失われ enum/sealed でもunwrapErr()がmixed厳密性の確認:
HttpError::Forbiddenアームを一時的に外すとMatch expression does not handle remaining value:で解析エラーになることを確認済み（ケース漏れが検出される＝網羅が強制されている）。ドキュメント（
README.md）Type Safety セクションに Exhaustive error matching の項目を追加:
Eが enum /@phpstan-sealedunion なら、エラー値の網羅分岐を PHPStan が強制するisErr()+unwrapErr()かmatch()のerrアームで取り出す（instanceof Errは E をmixedに落とすので不可）instanceofには型引数喪失は起きない確認
phpstan analyse（level max）: No errorsphpunit: 69 tests OK（既存退行なし）php-cs-fixer --dry-run: 整形差分なし