a long time ago, when Swift Testing first came out, it was discovered that many types of parsers could not run within a Swift Testing suite, because Swift Testing attached some runtime hook to Swift’s error propagation (_swift_setWillThrowHandler), and this resulted in an unacceptable slowdown in parser performance, due to the parser using Swift errors internally for its control flow.
this is virtually unnoticeable in normal production builds, as it gets optimized out, but in a Swift Testing test suite, parsing slows to a crawl, as errors will be thrown and caught inside the parser on virtually every UTF-8 byte. this can cause parsing to become hundreds of times slower.
in some unit tests, this is tolerable, because payloads are small enough that even a 200x regression in parser performance still completes in a reasonable amount of time. but for more complex tests that involve loading some real-world data (like a 5 MB JSON file), this is a total blocker preventing Swift Testing adoption.
in Swift 6.3, is still no way to safely disable _swift_setWillThrowHandler for a single test suite?