DeallocTests 4.0: dependency injection as a package trait, deprecate DeallocTester

[DanielCech]

Stacked on #20 → #19 → #18. Merge those first. GitHub will then retarget this PR to master.

⚠️ This is the breaking 4.0 release. The README has a "Migrating to 4.0" section.

Why

Since the beginning, DeallocTests has come in two flavours: DeallocTests (with STRV Dependency Injection) and DeallocTestsDIFree. They were built from one symlinked source folder with conditional compilation. That has three costs:

• Everyone downloads STRV's DI library, even people who never use it.
• The symlink and conditional-compilation setup is fragile (Reliable dealloc checks, real tests and CI (3.1) #18 already had to work around it).
• Two products with two module names confuse people, and the README had to explain which one to pick.

Swift 6.1 added package traits, the official way to make part of a package optional. And since #19, there's a simpler API (expectDeallocation) that makes the original DeallocTester unnecessary.

What changes for users

One product; dependency injection is on by default, with an opt-out

There's now a single DeallocTests product. STRV Dependency Injection support is the DependencyInjection trait, which is on by default, because most of our projects use it. Projects that don't can turn it off:

// Most projects: nothing to configure, STRV Dependency Injection support included
.package(url: "https://github.com/strvcom/DeallocTests.git", from: "4.0.0")

// Projects without STRV Dependency Injection: the dependency isn't even downloaded
.package(url: "https://github.com/strvcom/DeallocTests.git", from: "4.0.0", traits: [])

What I verified:

• SwiftPM: with a test consumer package, the default pins ios-dependency-injection, and traits: [] creates no pin at all.
• Xcode projects: the DI sample uses the default, and Xcode checks out the DI package. The DIFree sample has an empty traits = ( ); on its package reference, and Xcode doesn't check it out at all. There's a known report of Xcode ignoring disabled default traits in some workspace setups, but it doesn't affect a regular project with a package reference.
• Turning the trait off from an Xcode project needs Xcode 26.4 or later. The common case (on) needs no configuration, so it works with any Xcode that supports Swift 6.1.

DeallocTester is deprecated

DeallocTester, DeallocTest and DeallocTestable still work, but they show deprecation warnings pointing to expectDeallocation. They'll be removed in 5.0. The README has a before/after example and a table mapping every old feature to its replacement (checkClasses → trackForDeallocation, actionBeforeCheck → afterRelease, and so on).

Removed

• The DeallocTestsDIFree product. Use DeallocTests and import DeallocTests.
• DefaultInitializable (deprecated in 3.1, unrelated to dealloc testing).

New minimums

• Swift 6.1 / Xcode 16.3 (needed for package traits).
• Xcode 26.4 only if you enable the trait from an Xcode project.

Sample apps

• DeallocTestsAppDIFreeSPM is now the XCTest example of expectDeallocation. It has no conformances file, and each screen is a one-line test. The deliberate leak is reported on the test's line with the someClosure hint.
• DeallocTestsAppDIFreeSPM also shows the opt-out: its Xcode project turns the trait off.
• DeallocTestsAppSPM uses the default trait and is the Swift Testing example. Its DeallocTester tests stay as a reference for the deprecated API.

Tests and CI

• swift test passes in the default configuration and with --disable-default-traits (25 and 22 Swift Testing tests plus the XCTest suites). The library builds with zero warnings in both.
• iOS simulator package tests pass (28 Swift Testing tests).
• Both sample apps tested on the simulator. The only failure is the intentional leak.
• CI now runs the macOS tests in both trait configurations. The sample builds moved to the macos-26 runner, because traits in an Xcode project need Xcode 26.4.

Upgrading STRV projects

• Projects using DeallocTests with STRV Dependency Injection: bump to 4.0. Nothing else is required, but DeallocTester tests now show deprecation warnings.
• Projects using DeallocTestsDIFree: switch to the DeallocTests product and import DeallocTests, and turn off the default trait.

🤖 Generated with Claude Code