DeallocTests 4.0 (3/5): trackForDeallocation, leak hints and Dependency Injection support

[DanielCech]

Part 3 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.

Beyond one object: check owned objects and any unit test's system under test, explain leaks, and check dependencies from a Dependency Injection container.

Why

• Only the root was watched in 3.x: a screen can deallocate while its view model leaks. checkClasses only worked for classes that installed tracking themselves, in app code.
• No Swift Testing teardown: the most common leak check in the wild, a weak reference in an XCTest teardown block, has no equivalent there.
• "X was not deallocated" says that, not why. The only aid in 3.x was Alloc/Dealloc console output.
• Shared registrations look like leaks: .shared registrations live in the container. 3.x only handled this inside a DeallocTester subclass.

What changes

trackForDeallocation

// Inside expectDeallocation: checked together with the screen
await expectDeallocation(.present) {
    let viewModel = trackForDeallocation(ProfileViewModel())
    return ProfileViewController(viewModel: viewModel)
}

// Any Swift Testing test or suite
@Test(.checksDeallocation) func loadsProfile() async {
    let viewModel = trackForDeallocation(ProfileViewModel(api: MockAPI()))
    await viewModel.load()
}

// XCTest: a method on the test case, checked at teardown
let viewModel = trackForDeallocation(ProfileViewModel(api: MockAPI()))

A call without the trait or an enclosing check is reported instead of silently checking nothing.

Leak hints

App.ProfileViewController was not deallocated within 2 sec. Possible causes:
  • `onUpdate` is a closure. Make sure it captures self weakly
  • `self.child.parent` refers back to the object. That's a retain cycle unless one of the references is weak
  • Or something outside still holds it: a parent's list of children, a cache or a singleton

• Detects closures, Tasks, Combine subscriptions, timers and reference cycles through properties.
• Skips nil and empty values, shows @Observable names, and doesn't follow Apple framework objects.
• Deliberately not done: checking every reachable object. Mirror can't tell weak from strong, so a weak delegate would be a false leak. Hints are computed only for a confirmed leak and phrased as suggestions.

Dependency Injection (with the default trait)

await expectDeallocation(of: APIManaging.self, resolvedFrom: container)

The dependency is resolved, the container's shared instances are released, then the check runs. A value type is reported with its concrete type, because checking a boxed copy would always pass.

How to review

Order	File	What
1	Expectation/TrackForDeallocation.swift	both entry points and the trait; the tracker becomes a task-local
2	Diagnostics/LeakHints.swift, LeakReport.swift	reflection (bounded in depth and size) and message
3	Expectation/ExpectDeallocation+DependencyInjection.swift	71 lines

Source +398, tests +327.

Testing

Tracking in tests, suites, parameterized tests, nested and XCTest; one leak case per hint kind; DI shared/new/value type. Green on macOS (both trait settings) and the iOS Simulator.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

The Swift Testing trait skips deallocation verification whenever the test body throws.

Review effort: Balanced
Findings: 1

Open (1)

• Deallocation verification skipped when test body throws · New

What changed in this PR

Adds broader deallocation tracking, diagnostic leak hints, and Dependency Injection container support.

Changes:

• Adds trackForDeallocation for Swift Testing and XCTest.
• Generates reflection-based leak hints.
• Adds AsyncContainer dependency checks and related tests.

File	Description
Package.swift	Adds conditional DI test dependency.
Sources/​DeallocTests/​Diagnostics/​LeakHints.swift	Detects likely leak causes.
Sources/​DeallocTests/​Diagnostics/​LeakReport.swift	Includes hints in reports.
Sources/​DeallocTests/​Expectation/​DeallocationTracker.swift	Supports task-local tracking and hints.
Sources/​DeallocTests/​Expectation/​ExpectDeallocation+DependencyInjection.swift	Adds DI resolution checks.
Sources/​DeallocTests/​Expectation/​ExpectDeallocation.swift	Tracks nested objects.
Sources/​DeallocTests/​Expectation/​TrackForDeallocation.swift	Adds tracking APIs and trait.
Tests/​DeallocTestsTests/​ExpectDeallocationTests.swift	Tests tracking and DI support.
Tests/​DeallocTestsTests/​LeakHintsAndSwiftUITests.swift	Tests hints and nested tracking.
Tests/​DeallocTestsTests/​LeakReportTests.swift	Tests hint generation and formatting.
Tests/​DeallocTestsTests/​TrackForDeallocationXCTests.swift	Tests XCTest tracking.

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