cannot find type SendableMetatype in scope

[CamJN]

I cannot compile this package (specifically the bash completion step) with the latest swift compiler available from the CLT and the SDKROOT set to /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk, like homebrew does.

ArgumentParser version: 1.6.1
Swift version:

swift-driver version: 1.127.14.1
Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1)
Target: x86_64-apple-macosx15.0

CLT version: 26.0.0.0.1.1757719676
macOS version: 15.7.1 (24G231)

Checklist

• If possible, I've reproduced the issue using the main branch of this package
• I've searched for existing GitHub issues

Steps to Reproduce

git clone git@github.com:CamJN/aliasPath.git
cd aliasPath
export SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk
make

Expected behaviour

swift-argument-parser can compile with swift 6.2 compiler, and macOS 15 SDK.

Actual behaviour

...snip
 23 [8/10] Compiling ArgumentParser BashCompletionsGenerator.swift
 24 /private/tmp/alias-path-20251013-91126-xovrpd/aliasPath-1.0.0/.build/checkouts/swift-argument-parser/Sources/ArgumentParser/Utilities/SwiftExtensions.swift:14:45: error: cannot find type 'SendableMetatype' in scope
 25 12 | #if compiler(>=6.2)
 26 13 | /// Designates a type as having a sendable metatype.
 27 14 | @_marker public protocol _SendableMetatype: SendableMetatype {}
 28    |                                             `- error: cannot find type 'SendableMetatype' in scope
 29 15 | #else
 30 16 | @_marker public protocol _SendableMetatype {}
 31 make: *** [/private/tmp/alias-path-20251013-91126-xovrpd/aliasPath-1.0.0/.build/x86_64-apple-macosx/release/aliasPath] Error 1
 32