Merge main into release/6.4.x#1727
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stmontgomery merged 4 commits intoMay 27, 2026
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This PR adds helper members on `Trait` to allow casting between the different refining protocols and concrete trait types without relying on `as?` in Embedded Swift. I have left an `as? TimeLimitTrait` cast unmodified as I expect we won't support time limits in Embedded Swift and will probably just stub out that whole type. ### Checklist: - [x] Code and documentation should follow the style of the [Style Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md). - [x] If public symbols are renamed or modified, DocC references should be updated.
Add more concrete overloads of `String(describingForTest:)` and `appendInterpolation(_:)` to eliminate more string-related diagnostics. And a few other related changes. ### Checklist: - [x] Code and documentation should follow the style of the [Style Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md). - [x] If public symbols are renamed or modified, DocC references should be updated.
Enable targeted interoperability by default
### Motivation:
Interoperability is a feature that makes it safer and easier than ever
to migrate from XCTest to Swift Testing.
It does this by addressing the problem of "lossy without interop", where
issues created by XCTest are normally not handled in a Swift Testing
test.
Interop supports a few modes:
class FooTests: XCTestCase {
func testInterop() {
// None: No-op
// Limited: ❌ "Interop failure"
// Complete: ❌ "Interop failure"
// Strict: ❌ "Interop failure"
Issue.record("Interop failure")
}
}
@test func `Test Interop`() {
// None: No-op
// Limited: ⚠️ "Interop failure", ⚠️ Adopt Swift Testing primitives
// Complete: ❌ "Interop failure", ⚠️ Adopt Swift Testing primitives
// Strict: 💥 fatalError: Adopt Swift Testing primitives
XCTFail("Interop failure")
}
The default is "complete" for `swift-tools-version: 6.4`[^1] and
"limited" otherwise.
Use env var `SWIFT_TESTING_XCTEST_INTEROP_MODE=<mode in lowercase>` to
override this mode at runtime.
[^1]: swiftlang/swift-package-manager#9857
To learn more, refer to the full proposal:
https://github.com/swiftlang/swift-evolution/blob/main/proposals/testing/0021-targeted-interoperability-swift-testing-and-xctest.md
### Modifications:
* Remove SWT_EXPERIMENTAL_INTEROP_ENABLED flag and related checks. This
ensures that interoperability Just Works when you use a toolchain that
supports it.
* Add SWIFT_TESTING_XCTEST_INTEROP_MODE to EnvironmentVariables.md
Resolves rdar://177175523
## Checklist:
- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.
---------
Co-authored-by: Stuart Montgomery <smontgomery@apple.com>
stmontgomery
requested review from
briancroom,
grynspan,
harlanhaskins,
jerryjrchen and
stmontgomery
as code owners
stmontgomery
approved these changes
May 27, 2026
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