Unable to Specify @MainActor for a closure with empty parameters

[omochi]

Description

Unable to specify @MainActor for a closure with explicit empty parameters

Reproduction

The following code does not compile:

Task { @MainActor () in
}
// error: Extraneous whitespace between attribute name and '('

Expected behavior

This compiles.

Environment

$ swift --version
swift-driver version: 1.115 Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2)
Target: arm64-apple-macosx15.0

Additional information

No response

[HeMet]

It works without parenthesis

Task { @MainActor in }

[omochi]

Thank you for the information.
I’m aware that this case can be written in the way you described.

However, that approach relies on type inference for function parameters, which is different from what I’m trying to report.
The issue I’m raising is that it’s not possible to explicitly specify the function parameters.

For example, in the following code, the two approaches have different meanings:

let parameterInferred = { @MainActor in
    print($0, $1)
}

let parameterExplicit = { @MainActor() () in
    print($0, $1)
}

In parameterInferred, since the parameters are not explicitly specified, the types are inferred from the implementation, and the result is a function with two parameters.

In parameterExplicit, because the parameters are explicitly specified, this results in a compile-time error. I have added two sets of parentheses as a workaround for this bug.

As these two approaches have different meanings, it is inconvenient that the latter form cannot be used.