DeallocTests 4.0 (2/5): expectDeallocation with UIKit, AppKit and SwiftUI lifecycles

[DanielCech]

Part 2 of 5. DeallocTests 4.0 series (merge in order): #25 groundwork → #26 expectDeallocation → #27 tracking, hints, DI → #28 configuration → #29 remove legacy, docs. Why 4.0, the breaking changes and the alternatives we looked at: see #25.

The new API: expectDeallocation, with lifecycles for UIKit, AppKit and SwiftUI. It works in Swift Testing and XCTest; DeallocTester keeps working next to it until part 5.

Why

• 3.x needs a DeallocTestable conformance per tested class, a DeallocTester subclass and an expectation per test, and works in XCTest only.
• Its checks sleep for fixed times, match leaks by class (a freed instance hides a leaked one), and report failures inside the library.
• Many leaks only appear once a view controller loads its view or appears on screen, or once a SwiftUI view runs onAppear/.task. 3.x always presented modally and waited for UIKit completion handlers that might never come, and had no SwiftUI story.

What changes

await expectDeallocation { ProfileViewModel() }
await expectDeallocation(.present) { coordinator.makeProfileViewController() }
await expectDeallocation(.push(interaction: { $0.refresh() })) { makeController() }
await expectDeallocation(.hosting { ProfileView(viewModel: $0) }) { ProfileViewModel() }

• Weak reference instead of conformances: any class, each instance checked separately.
• Polling with a deadline: a passing check returns as soon as the object is gone; a leak fails after the timeout (2 s).
• Reported at the test's line, to exactly one framework: Swift Testing inside a @Test, XCTest otherwise. Since Swift 6.4 each framework also records the other's failures, so reporting to both would show every leak twice.
• Lifecycles: .none, .custom, .loadView (UIKit, AppKit), .present(style:interaction:), .push(interaction:), .hosting(interaction:) (UIKit and AppKit hosting).
• UIKit steps wait for UIKit's state (appeared, dismissed, popped), up to 10 s, instead of completion handlers. A test can fail but can't hang. A lifecycle that can't run says why (e.g. modal presentation needs a host app) and skips the check.
• Readable type names (also for private types), locale-independent durations, afterRelease for clearing caches before the check, nothing reported for a cancelled test.
• The package has tests again; CI runs them on macOS (with and without the trait) and on the iOS Simulator.

How to review

Order	File	What
1	Expectation/ExpectDeallocation.swift	the public function
2	Expectation/DeallocationTracker.swift, Polling.swift	weak references, polling, reporting
3	Expectation/IssueReporting.swift	Swift Testing vs XCTest routing
4	Expectation/Lifecycle.swift	.none, .custom, then UIKit (TestWindow, HostViewController) and AppKit
5	Expectation/Lifecycle+SwiftUI.swift	.hosting
6	Diagnostics/	message text, type names, durations

Source +574, tests +425.

Testing

ExpectDeallocationTests, UIKitLifecycleTests, SwiftUIHostingTests, LeakReportTests and an XCTest class showing the same call works there. Green on macOS (both trait settings) and the iOS Simulator. .present needs a host app, so it's skipped in package tests and covered by the sample apps in part 5.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

Cancellation, deadline handling, cleanup, and UI lifecycle edge cases can produce false results or failures.

Review effort: Balanced
Findings: 1 · 6

Open (7)

• Anchor popover presentations before presenting · New
• Run afterRelease when lifecycle execution cannot start · New
• Await SwiftUI appearance instead of using a fixed sleep · New
• Handle CancellationError without recording a lifecycle failure · New
• Preserve cancellation instead of reporting it as a timeout · New
• Check timeout deadline before accepting post-sleep results · New
• Cancel the expected-leak task after observing the issue · New

What changed in this PR

Adds expectDeallocation, providing weak-reference leak checks and UI lifecycle support across Swift Testing and XCTest.

Changes:

• Adds polling, diagnostics, source-location reporting, and cleanup hooks.
• Adds UIKit, AppKit, and SwiftUI lifecycles.
• Restores package tests and expands CI to execute them.

File	Description
.github/​workflows/​ci.yml	Runs macOS and iOS Simulator tests.
Package.swift	Adds the test target.
Sources/​DeallocTests/​Diagnostics/​DurationText.swift	Formats durations consistently.
Sources/​DeallocTests/​Diagnostics/​LeakReport.swift	Builds leak diagnostics.
Sources/​DeallocTests/​Diagnostics/​TypeNames.swift	Produces readable type names.
Sources/​DeallocTests/​Expectation/​DeallocationTracker.swift	Tracks weak references and reports leaks.
Sources/​DeallocTests/​Expectation/​ExpectDeallocation.swift	Implements the public API.
Sources/​DeallocTests/​Expectation/​IssueReporting.swift	Routes failures to the active test framework.
Sources/​DeallocTests/​Expectation/​Lifecycle+SwiftUI.swift	Adds SwiftUI hosting lifecycles.
Sources/​DeallocTests/​Expectation/​Lifecycle.swift	Adds custom, UIKit, and AppKit lifecycles.
Sources/​DeallocTests/​Expectation/​Polling.swift	Implements deadline-based polling.
Tests/​DeallocTestsTests/​ExpectDeallocationTests.swift	Tests core API behavior.
Tests/​DeallocTestsTests/​LeakHintsAndSwiftUITests.swift	Tests SwiftUI task lifecycles.
Tests/​DeallocTestsTests/​LeakReportTests.swift	Tests diagnostics and polling.
Tests/​DeallocTestsTests/​TrackForDeallocationXCTests.swift	Verifies XCTest integration.
Tests/​DeallocTestsTests/​UIKitLifecycleTests.swift	Tests UIKit lifecycle behavior.

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[ipek]

Reviewed the incremental changes in PR #26. One reproduced issue is noted inline.

[ipek]

This catches any CancellationError, including one thrown by a child inside .custom while the outer test task is still active. I reproduced a child throwing before the interaction completed: expectDeallocation recorded no issue and the test passed, skipping the remaining lifecycle work. Could this return only when the outer task is canceled, and report the error otherwise?