Using sending with parameter packs crashes the compiler

[dehesa]

Description

I noticed compiler crashes while writing code in Xcode 16 Beta 6 transferring non-sendable values. I managed to boil it down to the reproduction below.

I brought it up in the Swift Forums and I was told by @slavapestov that sending is currently not supported in conjunction with parameter packs. That is good to know, but I think the compiler shouldn't crash, anyways.

Please notice, I am aware the code below is not "technically" correct. You can also make the compiler crash by writing the sending keywords in different places.

Reproduction

import Testing

@Test func testVariadic() async throws {
  let runner = Runner()
  await runner.run(1, 2, "3", "Paco", 5)
}

struct Runner {
  func run<each V>(_ value: repeat (sending each V)) async {
    let params = Wrapper(repeat each value)
    await compute(params)
  }
}

@MainActor func compute<each V>(_ value: Wrapper<repeat each V>) {
  for v in repeat each value.parameters {
    print(v)
  }
}

struct Wrapper<each V> {
  let parameters: (repeat each V)

  init(_ parameters: repeat each V) {
    self.parameters = (repeat each parameters)
  }
}

Stack dump

Stack dump:
0.	Program arguments: /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c /Users/marcos/Developer/Github/Private/swift-belt/sqlite-utils/tests/Issue.swift -primary-file /Users/marcos/Developer/Github/Private/swift-belt/sqlite-utils/tests/SQLiteTests.swift -emit-dependencies-path /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.d -emit-const-values-path /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.swiftconstvalues -emit-reference-dependencies-path /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.swiftdeps -serialize-diagnostics-path /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.dia -target arm64-apple-macos15.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -stack-check -sdk /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk -I /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug -I /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/PackageFrameworks -F /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug -F /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -no-color-diagnostics -enable-testing -g -debug-info-format=dwarf -dwarf-version=5 -module-cache-path /Users/marcos/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -profile-generate -profile-coverage-mapping -swift-version 6 -enforce-exclusivity=checked -Onone -D SWIFT_PACKAGE -D DEBUG -D Xcode -warn-long-function-bodies=80 -warn-long-expression-type-checking=30 -serialize-debugging-options -const-gather-protocols-file /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteUtilsTests_const_extract_protocols.json -enable-experimental-feature AccessLevelOnImport -enable-experimental-feature DebugDescriptionMacro -enable-experimental-feature OpaqueTypeErasure -enable-upcoming-feature ExistentialAny -enable-upcoming-feature InternalImportsByDefault -empty-abi-descriptor -plugin-path /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins/testing -validate-clang-modules-once -clang-build-session-file /Users/marcos/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -Xcc -working-directory -Xcc /Users/marcos/Developer/Github/Private/swift-belt -resource-dir /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/marcos/Developer/Github/Private/swift-belt -Xcc -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG -Xcc -ivfsstatcache -Xcc /Users/marcos/Library/Developer/Xcode/DerivedData/SDKStatCaches.noindex/macosx15.0-24A5324a-b8eb52f7cfe01464b1c5d9af15dcd1f8.sdkstatcache -Xcc -I/Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/SourcePackages/checkouts/swift-numerics/Sources/_NumericsShims/include -Xcc -I/Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Products/Debug/include -Xcc -I/Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/DerivedSources-normal/arm64 -Xcc -I/Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/DerivedSources/arm64 -Xcc -I/Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/DerivedSources -Xcc -DSWIFT_PACKAGE -Xcc -DDEBUG=1 -module-name SQLiteUtilsTests -package-name sqlite_utils -frontend-parseable-output -disable-clang-spi -target-sdk-version 15.0 -target-sdk-name macosx15.0 -external-plugin-path /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode-16.0.0-Beta.6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -o /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Build/Intermediates.noindex/sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.o -index-unit-output-path /sqlite-utils.build/Debug/SQLiteUtilsTests.build/Objects-normal/arm64/SQLiteTests.o -index-store-path /Users/marcos/Library/Developer/Xcode/DerivedData/Swift-cjsehycdxjrugnaogsxofvkblzer/Index.noindex/DataStore -index-system-modules
1.	Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2)
2.	Compiling with the current language version
3.	While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "/Users/marcos/Developer/Github/Private/swift-belt/sqlite-utils/tests/SQLiteTests.swift")
4.	While silgen emitFunction SIL function "@$s16SQLiteUtilsTests6RunnerV3runyyxxQpnYaRvzlF".
 for 'run(_:)' (at /Users/marcos/Developer/Github/Private/swift-belt/sqlite-utils/tests/SQLiteTests.swift:10:3)
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend           0x0000000107fa70fc llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x0000000107fa5350 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000107fa76c8 SignalHandler(int) + 292
3  libsystem_platform.dylib 0x0000000194658184 _sigtramp + 56
4  swift-frontend           0x0000000103455514 swift::Lowering::SILGenFunction::emitSemanticStore(swift::SILLocation, swift::SILValue, swift::SILValue, swift::Lowering::TypeLowering const&, swift::IsInitialization_t) + 1036
5  swift-frontend           0x00000001033d7dcc swift::Lowering::SingleBufferInitialization::copyOrInitValueIntoSingleBuffer(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, bool, swift::SILValue) + 148
6  swift-frontend           0x00000001034a3990 (anonymous namespace)::ArgumentInitHelper::emitParam(swift::ParamDecl*) + 1424
7  swift-frontend           0x00000001034a1f74 swift::Lowering::SILGenFunction::emitBasicProlog(swift::DeclContext*, swift::ParameterList*, swift::ParamDecl*, swift::Type, std::__1::optional<swift::Type>, swift::SourceLoc, unsigned int) + 2656
8  swift-frontend           0x000000010349f76c swift::Lowering::SILGenFunction::emitProlog(swift::DeclContext*, swift::CaptureInfo, swift::ParameterList*, swift::ParamDecl*, swift::Type, std::__1::optional<swift::Type>, swift::SourceLoc) + 160
9  swift-frontend           0x0000000103421c34 swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 212
10 swift-frontend           0x000000010336d8a0 swift::Lowering::SILGenModule::emitFunctionDefinition(swift::SILDeclRef, swift::SILFunction*) + 8420
11 swift-frontend           0x000000010336e140 swift::Lowering::SILGenModule::emitOrDelayFunction(swift::SILDeclRef) + 216
12 swift-frontend           0x000000010336b770 swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 364
13 swift-frontend           0x00000001034c1a10 (anonymous namespace)::SILGenType::visitFuncDecl(swift::FuncDecl*) + 32
14 swift-frontend           0x00000001034bdfb8 (anonymous namespace)::SILGenType::emitType() + 424
15 swift-frontend           0x000000010336b3a8 swift::ASTVisitor<swift::Lowering::SILGenModule, void, void, void, void, void, void>::visit(swift::Decl*) + 104
16 swift-frontend           0x0000000103371dbc swift::ASTLoweringRequest::evaluate(swift::Evaluator&, swift::ASTLoweringDescriptor) const + 1804
17 swift-frontend           0x00000001034a86b0 swift::SimpleRequest<swift::ASTLoweringRequest, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>> (swift::ASTLoweringDescriptor), (swift::RequestFlags)9>::evaluateRequest(swift::ASTLoweringRequest const&, swift::Evaluator&) + 196
18 swift-frontend           0x0000000103376c98 swift::ASTLoweringRequest::OutputType swift::Evaluator::getResultUncached<swift::ASTLoweringRequest, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()>(swift::ASTLoweringRequest const&, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()) + 528
19 swift-frontend           0x0000000102950f34 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 920
20 swift-frontend           0x0000000102954228 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1680
21 swift-frontend           0x0000000102952f58 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3572
22 swift-frontend           0x00000001028da01c swift::mainEntry(int, char const**) + 3680
23 dyld                     0x00000001942a0274 start + 2840

Expected behavior

No crashes and ideally future sending support by code blocks 😄

Environment

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