Translate Discovery.cpp to Swift #764
Assignees
Labels
enhancement
New feature or request
Comments
2 tasks
2 tasks
grynspan
added a commit
that referenced
this issue
Mar 11, 2025
This PR uses the experimental symbol linkage margers feature in the Swift compiler to emit metadata about tests (and exit tests) into a dedicated section of the test executable being built. At runtime, we discover that section and read out the tests from it. This has several benefits over our current model, which involves walking Swift's type metadata table looking for types that conform to a protocol: 1. We don't need to define that protocol as public API in Swift Testing, 1. We don't need to emit type metadata (much larger than what we really need) for every test function, 1. We don't need to duplicate a large chunk of the Swift ABI sources in order to walk the type metadata table correctly, and 1. Almost all the new code is written in Swift, whereas the code it is intended to replace could not be fully represented in Swift and needed to be written in C++. This change will be necessary to support Embedded Swift because there is no type metadata section emitted for embedded targets. The change also opens up the possibility of supporting generic types in the future because we can emit metadata without needing to emit a nested type (which is not always valid in a generic context.) That's a "future direction" and not covered by this PR specifically. I've defined a layout for entries in the new `swift5_tests` section that should be flexible enough for us in the short-to-medium term and which lets us define additional arbitrary test content record types. The layout of this section is covered in depth in the new [TestContent.md](https://github.com/swiftlang/swift-testing/blob/main/Documentation/ABI/TestContent.md) article. This functionality is only available if a test target enables the experimental `"SymbolLinkageMarkers"` feature and only if Swift Testing is used as a package (not as a toolchain component.) We continue to emit protocol-conforming types for now—that code will be removed if and when the experimental feature is properly supported (modulo us adopting relevant changes to the feature's API.) ## See Also #735 #764 swiftlang/swift#76698 swiftlang/swift#78411 ### 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.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
We should try to translate as much of Discovery.cpp to Swift as we can once we have proper test metadata emission (per #745.) We can't do it now because we're directly touching the type metadata machinery and end up deadlocking on Darwin (and probably other platforms, I haven't checked recently.)
The text was updated successfully, but these errors were encountered: