[6.1] Compilation fails when body macro is applied to function with closure capture list

[davdroman]

Description

When applying a body macro to a function, compilation fails if the function contains a closure with a capture list.

Removing either the macro or the capture resolves the issue.

Reproduction

class Demo {
	@NoOpBodyMacro // this macro does nothing but return the body as-is, so it's fundamentally a no-op
	func demo() {
		let closure = { [weak self] in // 🛑 error: Type of expression is ambiguous without a type annotation
			// no-op
		}
	}
}

Build BodyMacroErrorDemo_2025-03-17T00-48-24.txt

Expected behavior

The code above compiles.

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.109.103 clang-1700.0.13.2)
Target: arm64-apple-macosx15.0
Xcode 16.3.0 beta 2

Additional information

No response

[swift-student]

We are experiencing the same issue. I made up a sample project to demonstrate the issue.

MacroClosureCaptureList.zip

[BlackWolf]

Can confirm this bug made it into the Xcode 16.3 release.

A potential workaround is to move the closure code into a helper method:

class Demo {
	@NoOpBodyMacro 
	func demo() {
		executeDemo()
	}

       func executeDemo() {
               let closure = { [weak self] in 
			// no-op
		}
      }
}

[gsabran]

Having the same issue