Optimizations to Backtrace.current().
#647
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grynspan
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…le buffer to Address
…make it clearer what it's there for
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Swift 6 introduces the typed throws feature to replace `rethrows` and to support error handling in Embedded Swift. This feature uses an ABI that differs from the one used by untyped (traditional) `throws` and as such, our hook into the runtime (`_swift_willThrow`) is insufficient to provide backtrace information for errors thrown this way. This PR adds support for capturing said backtraces _if and only if_ the thrown error is of reference type. Such errors have stable addresses that we can track over time, whereas errors of value type will be copied when used with typed throws. ~~I'm also taking the opportunity to implement some performance enhancements to `Backtrace`. It shouldn't get called _very_ frequently, but it also should be fast!~~ This PR is dependent on #647. ### 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.
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This PR optimizes
Backtrace.current():Arraystorage and is handled by the standard library._startCachingForThrownErrorsto__SWIFT_TESTING_IS_CAPTURING_A_BACKTRACE_FOR_A_THROWN_ERROR__. This symbol unavoidably shows up in backtraces captured whenswift_willThrowis called, so I gave it a name that (hopefully) clearly explains why it's there.Checklist: