#expect(try ...) from inside a closure causes "errors thrown from here are not handled" error

[gwynne]

Description

When the expression passed to #expect() contains try, and the #expect() call occurs inside a throwing closure, the compiler emits an "errors thrown from here are not handled" error.

Verified using Xcode 16.2, release/6.1 dev snapshot (2024-12-21), and main dev snapshot (2024-12-22).

Expected behavior

The try keyword should be usable inside the #expect() macro, as it is under non-closure conditions.

Actual behavior

The compiler refuses to compile the expression.

Steps to reproduce

See attached reproducer: TestPackage.zip

swift-testing version/commit hash

6.0.3

Swift & OS version (output of swift --version ; uname -a)

swift-driver version: 1.115.1 Apple Swift version 6.0.3 (swiftlang-6.0.3.1.10 clang-1600.0.30.1)
Target: arm64-apple-macosx15.0
Darwin MacBookPro 24.2.0 Darwin Kernel Version 24.2.0: Fri Dec  6 19:01:59 PST 2024; root:xnu-11215.61.5~2/RELEASE_ARM64_T6000 arm64

[grynspan]

Gwynne also reproed with:

$ TOOLCHAINS=$(plutil -extract CFBundleIdentifier raw /Library/Developer/Toolchains/swift-6.1-DEVELOPMENT-SNAPSHOT-2024-12-21-a.xctoolchain/Info.plist) swift --version
Apple Swift version 6.1-dev (LLVM dd0f3b29e584617, Swift 12fb6cb92508551)
Target: arm64-apple-macosx15.0

And:

$ TOOLCHAINS=$(plutil -extract CFBundleIdentifier raw /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-12-22-a.xctoolchain/Info.plist) swift --version
Apple Swift version 6.2-dev (LLVM 9f6c3d784782c34, Swift 55189bae8e55169)
Target: arm64-apple-macosx15.0

And with the experimental swift-testing branch at swiftlang/swift-testing#840 which produces completely different macro expansions.

Looks like a type-checking issue to me, so sending this along to swift.

[grynspan]

I suspect this is a duplicate of #75256.