search

swiftlang / swift

The Swift Programming Language
https://swift.org
Apache License 2.0
66.67k stars 10.28k forks source link

Compiler crash on generic function call #74729

Open El-Fitz opened 4 days ago

El-Fitz commented 4 days ago

Description

The compiler appears to crash when resolving a generic method. Perhaps due to an abuse of generics?

Reproduction

protocol Context: Sendable {}

protocol Service<ServiceContext> {
    associatedtype ServiceContext: Context
}

protocol Builder<BuilderContext> {
    associatedtype BuilderContext: Context

    init(context: BuilderContext?)

    func withContextReducer(
        reducer: @escaping @Sendable (_ context: BuilderContext?) async -> BuilderContext?
    ) -> Self

    func build() -> Result<any Service<BuilderContext>, Error>
}

final actor ServiceImplementation<ServiceContext: Context>: Service {
    var currentContext: ServiceContext?

    init(initialContext: ServiceContext?) {
        currentContext = initialContext
    }
}

final class BuilderImplementation<BuilderContext: Context>: Builder {
    var initialContext: BuilderContext? = nil

    init(context: BuilderContext?) {
        initialContext = context
    }

    func withContextReducer(
        reducer: @escaping @Sendable (_ context: BuilderContext?) async -> BuilderContext?
    ) -> Self {
        return self
    }

    func build() -> Result<any Service<BuilderContext>, Error> {
        return .success(
            ServiceImplementation(
                initialContext: initialContext
            )
        )
    }
}

enum BuilderFactory {
    // The generic parameter here makes the swift compiler crash
    static func create<T: Context>(context: T?) -> any Builder<T> {
        return BuilderImplementation(context: context)
    }
}

struct DemoContext: Context {
    let someValue: Int?

    public init(someValue: Int? = nil) {
        self.someValue = someValue
    }
}

public func testBuilding() {
        let builderResult: Result<any Service<DemoContext>, Error> = BuilderFactory.create(context: DemoContext())
            .withContextReducer(
                reducer: { (context: DemoContext?) -> DemoContext? in context }
            )
            .build()
    }

testBuilding()

But when using a generic type for the builder factory instead of a generic function, it builds successfully.

enum BuilderFactory<FactoryContext: Context> {
    // But having it as a generic type's method is perfectly fine
    static func create(context: FactoryContext?) -> any Builder<FactoryContext> {
        return BuilderImplementation(context: context)
    }
}

Stack dump

Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.      Program arguments: /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift -emit-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.d -emit-const-values-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftconstvalues -emit-reference-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftdeps -serialize-diagnostics-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.dia -target arm64-apple-ios17.0-simulator -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk -I /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -I /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/lib -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Library/Frameworks -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk/Developer/Library/Frameworks -no-color-diagnostics -enable-testing -g -debug-info-format=dwarf -dwarf-version=4 -module-cache-path /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -profile-generate -profile-coverage-mapping -swift-version 5 -enforce-exclusivity=checked -Onone -D SWIFT_PACKAGE -D DEBUG -D SWIFT_PM_SUPPORTS_SWIFT_TESTING -D Xcode -serialize-debugging-options -enable-experimental-opaque-type-erasure -const-gather-protocols-file /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/IntegrationTests_const_extract_protocols.json -enable-experimental-feature DebugDescriptionMacro -empty-abi-descriptor -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins/testing -validate-clang-modules-once -clang-build-session-file /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -Xcc -working-directory -Xcc /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -resource-dir /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -Xcc -ivfsstatcache -Xcc /Users/elfitz/Library/Developer/Xcode/DerivedData/SDKStatCaches.noindex/iphonesimulator18.0-22A5282g-f46cc61c0d4ec2f57568566c87a94c0a.sdkstatcache -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/include -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources-normal/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources -Xcc -DSWIFT_PACKAGE -Xcc -DDEBUG=1 -module-name IntegrationTests -package-name GenericService -frontend-parseable-output -disable-clang-spi -target-sdk-version 18.0 -target-sdk-name iphonesimulator18.0 -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -parse-as-library -o /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-unit-output-path /GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-store-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Index.noindex/DataStore -index-system-modules
1.      Apple Swift version 6.0 (swiftlang-6.0.0.3.300 clang-1600.0.20.10)
2.      Compiling with effective version 5.10
3.      While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "/Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift")
4.      While silgen emitFunction SIL function "@$s16IntegrationTests06SimpleB0C12testBuildingyyF".
 for 'testBuilding()' (at /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift:73:12)
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           0x0000000108919118 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 40
1  swift-frontend           0x0000000108916f19 llvm::sys::RunSignalHandlers() + 233
2  swift-frontend           0x00000001089196f9 SignalHandler(int) + 313
3  libsystem_platform.dylib 0x00007ff8120cafdd _sigtramp + 29
4  libsystem_platform.dylib 0x00000003124768c0 _sigtramp + 18446603383469684992
5  swift-frontend           0x0000000104451202 swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const + 66
6  swift-frontend           0x00000001043ec99c swift::rewriting::PropertyBag::getConcreteType(llvm::ArrayRef<swift::GenericTypeParamType*>, swift::rewriting::MutableTerm const&, swift::rewriting::PropertyMap const&) const + 332
7  swift-frontend           0x00000001043d6faa swift::rewriting::RequirementMachine::getLocalRequirements(swift::Type, llvm::ArrayRef<swift::GenericTypeParamType*>) const + 330
8  swift-frontend           0x00000001043127de swift::GenericSignatureImpl::getLocalRequirements(swift::Type) const + 542
9  swift-frontend           0x000000010430e08d swift::GenericEnvironment::getOrCreateArchetypeFromInterfaceType(swift::Type) + 61
10 swift-frontend           0x000000010446e9c7 getMemberForBaseType(swift::InFlightSubstitution&, swift::Type, swift::Type, swift::AssociatedTypeDecl*, swift::Identifier, unsigned int) + 695
11 swift-frontend           0x0000000104472fff std::__1::optional<swift::Type> llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*)>::callback_fn<substType(swift::Type, unsigned int, swift::InFlightSubstitution&)::$_0>(long, swift::TypeBase*) + 623
12 swift-frontend           0x0000000104451202 swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const + 66
13 swift-frontend           0x00000001044545c1 swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const::$_1::operator()(swift::Type, swift::TypePosition) const + 49
14 swift-frontend           0x0000000104452c0a swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const + 6730
15 swift-frontend           0x000000010445149f swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const + 735
16 swift-frontend           0x000000010445149f swift::Type::transformWithPosition(swift::TypePosition, llvm::function_ref<std::__1::optional<swift::Type> (swift::TypeBase*, swift::TypePosition)>) const + 735
17 swift-frontend           0x000000010446fa3e substType(swift::Type, unsigned int, swift::InFlightSubstitution&) + 254
18 swift-frontend           0x000000010446f8e2 swift::Type::subst(swift::SubstitutionMap, swift::SubstOptions) const + 610
19 swift-frontend           0x00000001044737c4 swift::Type llvm::function_ref<swift::Type (swift::Type)>::callback_fn<swift::GenericFunctionType::substGenericArgs(swift::SubstitutionMap, swift::SubstOptions)::$_0>(long, swift::Type) + 100
20 swift-frontend           0x000000010446ddc8 swift::GenericFunctionType::substGenericArgs(llvm::function_ref<swift::Type (swift::Type)>) const + 152
21 swift-frontend           0x0000000103286b86 (anonymous namespace)::Callee::getSubstFormalInterfaceType(swift::CanTypeWrapper<swift::AnyFunctionType>, swift::SubstitutionMap) + 134
22 swift-frontend           0x0000000103270de3 (anonymous namespace)::Callee::forWitnessMethod(swift::Lowering::SILGenFunction&, swift::CanType, swift::SILDeclRef, swift::SubstitutionMap, swift::SILLocation) + 691
23 swift-frontend           0x000000010328555f (anonymous namespace)::SILGenApply::visitDeclRefExpr(swift::DeclRefExpr*) + 6495
24 swift-frontend           0x000000010326a8d9 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 345
25 swift-frontend           0x00000001032f902a swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 842
26 swift-frontend           0x00000001032ea7f8 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 40
27 swift-frontend           0x00000001033166b7 swift::Lowering::ManagedValue llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>::callback_fn<(anonymous namespace)::RValueEmitter::visitErasureExpr(swift::ErasureExpr*, swift::Lowering::SGFContext)::$_0>(long, swift::Lowering::SGFContext) + 71
28 swift-frontend           0x00000001032cae75 void llvm::function_ref<void (swift::SILValue)>::callback_fn<swift::Lowering::SILGenFunction::emitExistentialErasure(swift::SILLocation, swift::CanType, swift::Lowering::TypeLowering const&, swift::Lowering::TypeLowering const&, llvm::ArrayRef<swift::ProtocolConformanceRef>, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>, bool)::$_3>(long, swift::SILValue) + 405
29 swift-frontend           0x00000001032c48a8 swift::Lowering::SILGenFunction::emitExistentialErasure(swift::SILLocation, swift::CanType, swift::Lowering::TypeLowering const&, swift::Lowering::TypeLowering const&, llvm::ArrayRef<swift::ProtocolConformanceRef>, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>, bool) + 1544
30 swift-frontend           0x000000010330772f (anonymous namespace)::RValueEmitter::visitErasureExpr(swift::ErasureExpr*, swift::Lowering::SGFContext) + 799
31 swift-frontend           0x00000001032f90a1 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 961
32 swift-frontend           0x000000010330434a (anonymous namespace)::RValueEmitter::visitOpenExistentialExpr(swift::OpenExistentialExpr*, swift::Lowering::SGFContext) + 1226
33 swift-frontend           0x00000001032f9007 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 807
34 swift-frontend           0x000000010330406a (anonymous namespace)::RValueEmitter::visitOpenExistentialExpr(swift::OpenExistentialExpr*, swift::Lowering::SGFContext) + 490
35 swift-frontend           0x00000001032f9007 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 807
36 swift-frontend           0x00000001032e6ec8 swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*, std::__1::optional<swift::SILLocation>) + 120
37 swift-frontend           0x00000001032cede2 swift::Lowering::SILGenFunction::emitPatternBinding(swift::PatternBindingDecl*, unsigned int, bool) + 2370
38 swift-frontend           0x00000001032d65e3 swift::ASTVisitor<swift::Lowering::SILGenFunction, void, void, void, void, void, void>::visit(swift::Decl*) + 115
39 swift-frontend           0x00000001033a5939 swift::ASTVisitor<(anonymous namespace)::StmtEmitter, void, void, void, void, void, void>::visit(swift::Stmt*) + 5897
40 swift-frontend           0x0000000103321414 swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 500
41 swift-frontend           0x0000000103254737 swift::Lowering::SILGenModule::emitFunctionDefinition(swift::SILDeclRef, swift::SILFunction*) + 8535
42 swift-frontend           0x0000000103254f97 swift::Lowering::SILGenModule::emitOrDelayFunction(swift::SILDeclRef) + 215
43 swift-frontend           0x00000001032525cd swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 173
44 swift-frontend           0x00000001033c1d99 (anonymous namespace)::SILGenType::visitFuncDecl(swift::FuncDecl*) + 25
45 swift-frontend           0x00000001033bd8fb (anonymous namespace)::SILGenType::emitType() + 427
46 swift-frontend           0x00000001032523a2 swift::ASTVisitor<swift::Lowering::SILGenModule, void, void, void, void, void, void>::visit(swift::Decl*) + 82
47 swift-frontend           0x0000000103258e7d swift::ASTLoweringRequest::evaluate(swift::Evaluator&, swift::ASTLoweringDescriptor) const + 2365
48 swift-frontend           0x00000001033a3ee3 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&) + 179
49 swift-frontend           0x000000010325e97d 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'()) + 589
50 swift-frontend           0x000000010272e2e4 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 852
51 swift-frontend           0x0000000102733eeb performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 4699
52 swift-frontend           0x0000000102730ded swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 5581
53 swift-frontend           0x00000001026a2acd swift::mainEntry(int, char const**) + 5421
54 dyld                     0x000000020bfd6366 start + 1942
Command SwiftCompile failed with a nonzero exit code

Expected behavior

Successful compilation. Or a compilation error if this shouldn't build.

Environment

swift-driver version: 1.109.2 Apple Swift version 6.0 (swiftlang-6.0.0.3.300 clang-1600.0.20.10) Target: x86_64-apple-macosx14.0

But I also had it with Swift 5.10

Additional information

No response

El-Fitz commented 4 days ago

I think I've also reproduced it in another case, but here I can't figure out how to avoid this one.

Reproduction


protocol ContextDescriptor: Sendable {

}

protocol OutcomeDescriptor: Sendable {

}

protocol ResultDescriptor: Sendable {

}

protocol ErasedReducer<Context>: Sendable {
    associatedtype Context: ContextDescriptor
    associatedtype TriggerOutcome: OutcomeDescriptor
    associatedtype Result: ResultDescriptor

    var name: String { get }
    var function: @Sendable (_ context: Context?, _ trigger: TriggerOutcome) -> Result  { get }
}

protocol Reducer<Context, TriggerOutcome>: ErasedReducer {
    var name: String { get }
    var function: @Sendable (_ context: Context?, _ trigger: TriggerOutcome) -> Result  { get }
}

struct ExampleContext: ContextDescriptor {

}

struct ExampleOutcome: OutcomeDescriptor {

}

struct ExampleResult: ResultDescriptor {

}

struct ExampleReducer<Context: ContextDescriptor, TriggerOutcome: OutcomeDescriptor, Result: ResultDescriptor>: Reducer {
    let name: String
    let function: @Sendable (_ context: Context?, _ trigger: TriggerOutcome) -> Result
}

class ExampleService<Context: ContextDescriptor> {
    let reducers:  [any ErasedReducer<Context>]

    public init(reducers: [any ErasedReducer<Context>]) {
        self.reducers = reducers
    }

    func reduce<TriggerOutcome: OutcomeDescriptor>(outcome: TriggerOutcome, context: Context) -> (any ResultDescriptor)? {
        // This line appears to be what's causing the crash
        guard let reducer = (reducers.compactMap { reducer in reducer as? any Reducer<Context, TriggerOutcome> }).first else {
            return nil
        }
        return reducer.function(context, outcome)
    }
}

public class SimpleTest: XCTestCase {
    public func testReducing() {
        let erasedReducers: [any ErasedReducer<ExampleContext>] = [
            ExampleReducer<ExampleContext, ExampleOutcome, ExampleResult>(name: "Example", function: { (_, _) in ExampleResult() })
        ]
        let context = ExampleContext()
        let trigger = ExampleOutcome()

        let service = ExampleService<ExampleContext>(reducers: erasedReducers)

        service.reduce(outcome: trigger, context: context)
    }
}

Stack dump

Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.      Program arguments: /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift -emit-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.d -emit-const-values-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftconstvalues -emit-reference-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftdeps -serialize-diagnostics-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.dia -target arm64-apple-ios17.0-simulator -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk -I /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -I /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/lib -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Library/Frameworks -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk/Developer/Library/Frameworks -no-color-diagnostics -enable-testing -g -debug-info-format=dwarf -dwarf-version=4 -module-cache-path /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -profile-generate -profile-coverage-mapping -swift-version 5 -enforce-exclusivity=checked -Onone -D SWIFT_PACKAGE -D DEBUG -D SWIFT_PM_SUPPORTS_SWIFT_TESTING -D Xcode -serialize-debugging-options -enable-experimental-opaque-type-erasure -const-gather-protocols-file /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/IntegrationTests_const_extract_protocols.json -enable-experimental-feature DebugDescriptionMacro -empty-abi-descriptor -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins/testing -validate-clang-modules-once -clang-build-session-file /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -Xcc -working-directory -Xcc /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -resource-dir /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -Xcc -ivfsstatcache -Xcc /Users/elfitz/Library/Developer/Xcode/DerivedData/SDKStatCaches.noindex/iphonesimulator18.0-22A5282g-f46cc61c0d4ec2f57568566c87a94c0a.sdkstatcache -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/include -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources-normal/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources -Xcc -DSWIFT_PACKAGE -Xcc -DDEBUG=1 -module-name IntegrationTests -package-name GenericService -frontend-parseable-output -disable-clang-spi -target-sdk-version 18.0 -target-sdk-name iphonesimulator18.0 -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -parse-as-library -o /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-unit-output-path /GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-store-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Index.noindex/DataStore -index-system-modules
1.      Apple Swift version 6.0 (swiftlang-6.0.0.3.300 clang-1600.0.20.10)
2.      Compiling with effective version 5.10
3.      While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "/Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift")
4.      While silgen emitFunction SIL function "@$s16IntegrationTests14ExampleServiceC6reduce7outcome7contextAA16ResultDescriptor_pSgqd___xtAA07OutcomeI0Rd__lF".
 for 'reduce(outcome:context:)' (at /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift:56:5)
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           0x000000010893a118 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 40
1  swift-frontend           0x0000000108937f19 llvm::sys::RunSignalHandlers() + 233
2  swift-frontend           0x000000010893a6f9 SignalHandler(int) + 313
3  libsystem_platform.dylib 0x00007ff8120cafdd _sigtramp + 29
4  libsystem_platform.dylib 0x00000000d3994160 _sigtramp + 18446603373828149664
5  swift-frontend           0x00000001041025d7 swift::Mangle::ASTMangler::appendRequirement(swift::Requirement const&, swift::GenericSignature, bool) + 231
6  swift-frontend           0x0000000104100a50 swift::Mangle::ASTMangler::appendGenericSignatureParts(swift::GenericSignature, swift::Mangle::ASTMangler::GenericSignatureParts const&) + 240
7  swift-frontend           0x00000001040f1e52 swift::Mangle::ASTMangler::appendGenericSignature(swift::GenericSignature) + 194
8  swift-frontend           0x00000001040f4588 swift::Mangle::ASTMangler::mangleReabstractionThunkHelper(swift::CanTypeWrapper<swift::SILFunctionType>, swift::Type, swift::Type, swift::Type, swift::Type, swift::ModuleDecl*) + 184
9  swift-frontend           0x00000001033d4c51 swift::Lowering::SILGenModule::getOrCreateReabstractionThunk(swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanType, swift::CanType) + 1473
10 swift-frontend           0x000000010339faa1 createThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 4225
11 swift-frontend           0x0000000103392cc2 (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 2690
12 swift-frontend           0x0000000103392229 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::CanType, swift::CanType, swift::Lowering::SGFContext) + 441
13 swift-frontend           0x0000000103326d5f (anonymous namespace)::RValueEmitter::visitFunctionConversionExpr(swift::FunctionConversionExpr*, swift::Lowering::SGFContext) + 3263
SwiftCompile normal arm64 /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift (in target 'IntegrationTests' from project 'GenericService')
    cd /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode
    /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -c -primary-file /Users/elfitz/Projects/Personal/GenericService/Tests/IntegrationTests/GenericServiceTests/0-SimpleTests.swift -emit-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.d -emit-const-values-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftconstvalues -emit-reference-dependencies-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.swiftdeps -serialize-diagnostics-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.dia -target arm64-apple-ios17.0-simulator -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk -I /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -I /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/lib -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/PackageFrameworks -F /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Library/Frameworks -F /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator18.0.sdk/Developer/Library/Frameworks -no-color-diagnostics -enable-testing -g -debug-info-format\=dwarf -dwarf-version\=4 -module-cache-path /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -profile-generate -profile-coverage-mapping -swift-version 5 -enforce-exclusivity\=checked -Onone -D SWIFT_PACKAGE -D DEBUG -D SWIFT_PM_SUPPORTS_SWIFT_TESTING -D Xcode -serialize-debugging-options -enable-experimental-opaque-type-erasure -const-gather-protocols-file /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/IntegrationTests_const_extract_protocols.json -enable-experimental-feature DebugDescriptionMacro -empty-abi-descriptor -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins/testing -validate-clang-modules-once -clang-build-session-file /Users/elfitz/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -Xcc -working-directory -Xcc /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -resource-dir /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/elfitz/Projects/Personal/GenericService/.swiftpm/xcode -Xcc -ivfsstatcache -Xcc /Users/elfitz/Library/Developer/Xcode/DerivedData/SDKStatCaches.noindex/iphonesimulator18.0-22A5282g-f46cc61c0d4ec2f57568566c87a94c0a.sdkstatcache -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Products/Debug-iphonesimulator/include -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources-normal/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources/arm64 -Xcc -I/Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/DerivedSources -Xcc -DSWIFT_PACKAGE -Xcc -DDEBUG\=1 -module-name IntegrationTests -package-name GenericService -frontend-parseable-output -disable-clang-spi -target-sdk-version 18.0 -target-sdk-name iphonesimulator18.0 -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/swift/host/plugins\#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/local/lib/swift/host/plugins\#/Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode-16.0.0-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -parse-as-library -o /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Build/Intermediates.noindex/GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-unit-output-path /GenericService.build/Debug-iphonesimulator/IntegrationTests.build/Objects-normal/arm64/0-SimpleTests.o -index-store-path /Users/elfitz/Library/Developer/Xcode/DerivedData/GenericService-chzyvvkikbfrwuewbnavurdyadfw/Index.noindex/DataStore -index-system-modules

14 swift-frontend           0x000000010331a05a swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 890
15 swift-frontend           0x000000010332534a (anonymous namespace)::RValueEmitter::visitOpenExistentialExpr(swift::OpenExistentialExpr*, swift::Lowering::SGFContext) + 1226
16 swift-frontend           0x000000010331a007 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 807
17 swift-frontend           0x000000010330b7f8 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 40
18 swift-frontend           0x00000001032a7504 (anonymous namespace)::SILGenApply::visitExpr(swift::Expr*) + 36
19 swift-frontend           0x000000010328b8d9 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 345
20 swift-frontend           0x000000010331a02a swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 842
21 swift-frontend           0x0000000103337a9c swift::Lowering::ManagedValue llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::SGFContext)>::callback_fn<(anonymous namespace)::RValueEmitter::visitInjectIntoOptionalExpr(swift::InjectIntoOptionalExpr*, swift::Lowering::SGFContext)::$_0>(long, swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::SGFContext) + 44
22 swift-frontend           0x00000001032e3f24 swift::Lowering::SILGenFunction::emitOptionalSome(swift::SILLocation, swift::SILType, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::SGFContext)>, swift::Lowering::SGFContext) + 1284
23 swift-frontend           0x000000010332a45e (anonymous namespace)::RValueEmitter::visitInjectIntoOptionalExpr(swift::InjectIntoOptionalExpr*, swift::Lowering::SGFContext) + 1582
24 swift-frontend           0x000000010331a10e swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 1070
25 swift-frontend           0x0000000103307ec8 swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*, std::__1::optional<swift::SILLocation>) + 120
26 swift-frontend           0x00000001033cb0ea swift::Lowering::SILGenFunction::emitReturnExpr(swift::SILLocation, swift::Expr*) + 1706
27 swift-frontend           0x00000001033c6a48 swift::ASTVisitor<(anonymous namespace)::StmtEmitter, void, void, void, void, void, void>::visit(swift::Stmt*) + 6168
28 swift-frontend           0x0000000103342414 swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 500
29 swift-frontend           0x0000000103275737 swift::Lowering::SILGenModule::emitFunctionDefinition(swift::SILDeclRef, swift::SILFunction*) + 8535
30 swift-frontend           0x0000000103275f97 swift::Lowering::SILGenModule::emitOrDelayFunction(swift::SILDeclRef) + 215
31 swift-frontend           0x00000001032735cd swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 173
32 swift-frontend           0x00000001033e2d99 (anonymous namespace)::SILGenType::visitFuncDecl(swift::FuncDecl*) + 25
33 swift-frontend           0x00000001033de8fb (anonymous namespace)::SILGenType::emitType() + 427
34 swift-frontend           0x00000001032733a2 swift::ASTVisitor<swift::Lowering::SILGenModule, void, void, void, void, void, void>::visit(swift::Decl*) + 82
35 swift-frontend           0x0000000103279e7d swift::ASTLoweringRequest::evaluate(swift::Evaluator&, swift::ASTLoweringDescriptor) const + 2365
36 swift-frontend           0x00000001033c4ee3 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&) + 179
37 swift-frontend           0x000000010327f97d 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'()) + 589
38 swift-frontend           0x000000010274f2e4 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 852
39 swift-frontend           0x0000000102754eeb performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 4699
40 swift-frontend           0x0000000102751ded swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 5581
41 swift-frontend           0x00000001026c3acd swift::mainEntry(int, char const**) + 5421
42 dyld                     0x000000020c192366 start + 1942
Command SwiftCompile failed with a nonzero exit code
El-Fitz commented 4 days ago

And the second crash can be avoided by providing a method returning an existential instead of an associated type, and using this method instead of the generic closure property.

protocol Reducer<Context, TriggerOutcome>: ErasedReducer {
    var name: String { get }
    var function: @Sendable (_ context: Context?, _ trigger: TriggerOutcome) -> Result  { get }

    // Using this method instead of the `function` closure directly does not make the compiler crash
    func reduce(_ context: Context?, _ trigger: TriggerOutcome) -> any ResultDescriptor
}

extension Reducer {
    func reduce(_ context: Context?, _ trigger: TriggerOutcome) -> any ResultDescriptor {
        function(context, trigger)
    }
}

...

class ExampleService<Context: ContextDescriptor> {
    let reducers:  [any ErasedReducer<Context>]

    public init(reducers: [any ErasedReducer<Context>]) {
        self.reducers = reducers
    }

    func reduce<TriggerOutcome: OutcomeDescriptor>(outcome: TriggerOutcome, context: Context) -> (any ResultDescriptor)? {
        guard let reducer = (reducers.compactMap { reducer in reducer as? any Reducer<Context, TriggerOutcome> }).first else {
            return nil
        }
        return reducer.reduce(context, outcome)
    }
}