Swiftの “private” を テストする / Testing Swift "private"

Mobile Act OSAKA 15
https://mobileact.connpass.com/event/343364/

1. Swiftの “private” を テストする id:yutailang0119 / @yutailang0119 Mobile Act OSAKA 15 1
2. Who am I!? • id:yutailang0119 ◦ @yutailang0119 • 株式会社はてな ◦ @京都オフィス ◦ アプリケーションエンジニア ▪ iOS/Android ◦ サービスプラットフォームチーム • try! Swift Tokyo Organizer • AVP座談会 🥽 2
3. 3 Introduction
4. Introduction • private/fileprivateは、参照範囲を制限 ◦ @testableもアクセスできない ◦ open, package, internalはアクセス可能 • Javaには @VisibleForTesting がある ◦ https://developer.android.com/reference/androidx/annotation/VisibleForTesting 4
5. Access Level 5 • open • package • internal • fileprivate • private https://docs.swift.org/swift-book/documentation/the-swift-programming-language/accesscontrol/
6. 6 Motivation
7. Motivation • テストのためのinternalを避けたい ◦ e.g.) 🙅 コメントでの規制 VisibleForTesting • アクセスのバイパス手段がほしい 7
8. 8 Proposed solution
9. 9 yutailang0119/swift-bypass-accessing
10. yutailang0119/swift-bypass-accessing • Swift Macros ◦ @BypassAccess • ___ prefix付きコード生成 PeerMacro • #if DEBUG & internal 10
11. PeerMacro @attached(peer, names: prefixed(___), named(___init)) public macro BypassAccess() = #externalMacro( module: "BypassAccessingMacros", type: "BypassAccessMacro" ) 11
12. 12 Detailed design
13. Detailed design import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" @BypassAccess fileprivate func function() -> String { #function } } 13
14. Detailed design import Testing import BypassAccessing @testable import Example struct Tests { @Test func test() { let declaration = Declaration() #if DEBUG #expect(declaration.___property == "property") #expect(declaration.___function() == "function()") #endif } } 14
15. 15 Macro
16. Macro import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" } 16
17. Expand Macro import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" #if DEBUG var ___property: String { property } #endif } 17
18. Macro import BypassAccessing struct Declaration { @BypassAccess fileprivate func function() -> String { #function } } 18
19. Expand Macro import BypassAccessing struct Declaration { @BypassAccess fileprivate func function() -> String { #function } #if DEBUG func ___function() -> String { function() } #endif } 19
20. 20 Support Grammar
21. Support Grammar • let • var ◦ Stored ◦ Computed • func • init 21
22. Modifier, Accessor • async, @MainActor • throws • static, class • inout • Generics 22 https://docs.swift.org/swift-book/documentation/the-swift-programming-language/summaryofthegrammar
23. Modifier, Accessor 23 import BypassAccessing struct Declaration<Element> { @BypassAccess @MainActor private init(_ arg: inout String) async throws where Element: Equatable {} #if DEBUG @MainActor static func ___init(_ arg: inout String) async throws -> Self where Element: Equatable { try await Self.init(_: &arg) } #endif }
24. Limitation • ❌ privateが現れるインターフェース ◦ Method must be declared private because its parameter uses a private type • ❌ 型推論を伴うプロパティ ◦ 　 ◦ '@BypassAccess' attribute require TypeAnnotation 24 @BypassAccess private var value = "value"
25. Support Grammar • 想定利用ケースは、テストを参照 ◦ https://github.com/yutailang0119/swift-bypass-accessing/tree/main/Tests/BypassAccessingTests • 考慮外パターンが存在しそう🫥 25
26. 小噺 • SwiftSyntaxBuilder ◦ 複雑だが、今回のケースでは便利 ▪ 条件に応じて、Expressionを組み合わせ可能 ◦ PlainTextで実装後、SyntaxBuilderで書き直した • Macroのテストは swift-testing が使えない ◦ XCTest ◦ https://github.com/swiftlang/swift-syntax/issues/2720 26
27. 27 Conclusion
28. Conclusion • yutailang0119/swift-bypass-accessing ◦ @BypassAccess • 想定外を見つけたら、ご連絡ください📲 28
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