Swift compiler SEGV in Xcode10.

segv.swift

// ===========================
// Pattern1: SEGV in Xcode10(Swift4.2 or Swift4) ~ Xcode10.1(Swift 4.2.1)
// This code compilable in Xcode 9.4.1(Swift 4.1)
// ===========================

class A {}
protocol BProtocol {
    associatedtype Info: A
    var info: Info? { get set }
}
class B<T1: A>: BProtocol {
    var info: T1?
}
protocol CProtocol {
    associatedtype Property: BProtocol
    var property: Property? { get set }
}
class C<T2: B<A>>: CProtocol {
    var property: T2?
}

// ===========================
// Pattern2: not SEGV (Remove generic parameter from B class)
// ===========================

class A {}
protocol BProtocol {
    associatedtype Info: A
    var info: Info? { get set }
}
class B: BProtocol {
    var info: A?
}
protocol CProtocol {
    associatedtype Property: BProtocol
    var property: Property? { get set }
}
class C<T2: B>: CProtocol {
    var property: T2?
}

// ===========================
// Pattern3: not SEGV (Remove CProtocol)
// ===========================

class A {}
protocol BProtocol {
    associatedtype Info: A
    var info: Info? { get set }
}
class B<T1: A>: BProtocol {
    var info: T1?
}
class C<T2: B<A>> {
    var property: T2?
}

stacktrace.txt

0  swift                    0x0000000111cbe64a PrintStackTraceSignalHandler(void*) + 42
1  swift                    0x0000000111cbddfe SignalHandler(int) + 302
2  libsystem_platform.dylib 0x00007fff68bcbb3d _sigtramp + 29
3  libsystem_platform.dylib 0x00007fcb1b856a60 _sigtramp + 2999496512
4  swift                    0x000000010f0d2e59 swift::ConformanceChecker::ensureRequirementsAreSatisfied(bool)::GatherConformancesListener::satisfiedConformance(swift::Type, swift::Type, swift::ProtocolConformanceRef) + 201
5  swift                    0x000000010f0a8c2f swift::TypeChecker::checkGenericArguments(swift::DeclContext*, swift::SourceLoc, swift::SourceLoc, swift::Type, swift::ArrayRefView<swift::Type, swift::GenericTypeParamType*, swift::GenericTypeParamType* swift::staticCastHelper<swift::GenericTypeParamType>(swift::Type const&), true>, llvm::ArrayRef<swift::Requirement>, llvm::function_ref<swift::Type (swift::SubstitutableType*)>, llvm::function_ref<llvm::Optional<swift::ProtocolConformanceRef> (swift::CanType, swift::Type, swift::ProtocolType*)>, llvm::function_ref<bool (swift::TypeCheckRequest)>*, swift::OptionSet<swift::ConformanceCheckFlags, unsigned int>, swift::GenericRequirementsCheckListener*, swift::SubstOptions) + 1103
6  swift                    0x000000010f0d2bcd swift::ConformanceChecker::ensureRequirementsAreSatisfied(bool) + 1325
7  swift                    0x000000010f0ee4ba swift::ConformanceChecker::resolveTypeWitnesses() + 378
8  swift                    0x000000010f0be973 swift::MultiConformanceChecker::checkIndividualConformance(swift::NormalProtocolConformance*, bool) + 11347
9  swift                    0x000000010f0bb8c2 swift::MultiConformanceChecker::checkAllConformances() + 162
10 swift                    0x000000010f0d4ac7 swift::TypeChecker::checkConformancesInContext(swift::DeclContext*, swift::IterableDeclContext*) + 4279
11 swift                    0x000000010f11ef94 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int) + 2388
12 swift                    0x000000010ed5959e swift::CompilerInstance::performSema() + 4238
13 swift                    0x000000010df4659b performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 731
14 swift                    0x000000010df42dc5 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 7717
15 swift                    0x000000010dee8a35 main + 1349
16 libdyld.dylib            0x00007fff689e2085 start + 1
17 libdyld.dylib            0x000000000000004b start + 2539773895
Stack dump: