Open Radar

 
Summary:
The compiler crashes when I use the .Type of a generic type to populate the inferred or explicitly provided typealias of a protocol. That’s a bit hard to follow, but the steps to reproduce are easy.


Steps to Reproduce:
1. Write this code:

protocol A {
	typealias B
	func b(B)
}

struct X<Y> : A {
	func b(b: X.Type) {}
}

2. Try to compile it… if you dare.


Expected Results:
I expected it to compile and run just fine.


Actual Results:
The compiler crashed. SourceKitService crashes pretty hard too.

Makes no difference if you use struct, enum, or class, it always crashes. Likewise, using X<Y>.Type also crashes with the same backtrace.



Regression:
N/A


Notes:
3  libsystem_platform.dylib 0x00007fff5fb08208 _sigtramp + 3375770744
4  swift                    0x00000001001f0c60 swift::Lowering::ManagedValue::forwardInto(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::SILValue) + 160
5  swift                    0x0000000100241328 getThunkResult(swift::Lowering::SILGenFunction&, swift::SILLocation, TranslationKind, swift::CanTypeWrapper<swift::SILFunctionType>, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILValue, swift::SILValue, swift::SILValue) + 840
6  swift                    0x00000001002408dc swift::Lowering::SILGenFunction::emitProtocolWitness(swift::ProtocolConformance*, swift::SILDeclRef, swift::SILDeclRef, llvm::ArrayRef<swift::Substitution>, swift::Lowering::IsFreeFunctionWitness_t, swift::Lowering::HasInOutSelfAbstractionDifference_t) + 4236
7  swift                    0x000000010020fa75 swift::Lowering::SILGenModule::emitProtocolWitness(swift::ProtocolConformance*, swift::SILLinkage, swift::SILDeclRef, swift::SILDeclRef, swift::Lowering::IsFreeFunctionWitness_t, llvm::ArrayRef<swift::Substitution>) + 2741
8  swift                    0x00000001002105b2 (anonymous namespace)::SILGenConformance::emitFuncEntry(swift::FuncDecl*, swift::ValueDecl*, llvm::ArrayRef<swift::Substitution>) + 194
9  swift                    0x000000010020c85b swift::Lowering::SILGenModule::getWitnessTable(swift::ProtocolConformance*) + 1659
10 swift                    0x000000010021143b SILGenType::emitType() + 315
11 swift                    0x000000010020bf0e swift::Lowering::SILGenModule::visitNominalTypeDecl(swift::NominalTypeDecl*) + 30
12 swift                    0x00000001001fac8b swift::Lowering::SILGenModule::emitSourceFile(swift::SourceFile*, unsigned int) + 395
13 swift                    0x00000001001faf86 swift::SILModule::constructSIL(swift::Module*, swift::SourceFile*, unsigned int) + 406
14 swift                    0x00000001001fb012 swift::performSILGeneration(swift::Module*) + 18