Open Radar

 
Summary:
I’m getting reproducible crashes in the compiler with a Set type I’m writing. The starting code is available in this gist: https://gist.github.com/robrix/e9e6c6693382a579c62a


Steps to Reproduce:
1. Add (or if you’re using the gist, uncomment) this extension:

extension Set : Collection {
	var startIndex: DictionaryIndex<Element, Void> { return _dictionary.startIndex }
	var endIndex: DictionaryIndex<Element, Void> { return _dictionary.endIndex }
	
	subscript(index: DictionaryIndex<Element, Void>) -> Element {
		let (element, _) = _dictionary[index]
		return element
	}
}

2. Alternatively, change the definition of extend to use sequence directly by replacing:

for each in Element[](sequence)

with:

for each in sequence



Expected Results:
I expected both of these to work.


Actual Results:
The compiler crashes every time.


Regression:
N/A


Notes:
3  libsystem_platform.dylib 0x00007fff5ca034d0 _sigtramp + 3486641984
4  swift                    0x00000001033dc296 swift::serialization::Serializer::writeConformance(swift::ProtocolDecl const*, swift::ProtocolConformance const*, swift::Decl const*, std::__1::array<unsigned int, 256ul> const&, bool) + 1366
5  swift                    0x00000001033dd194 swift::serialization::Serializer::writeSubstitutions(llvm::ArrayRef<swift::Substitution>, std::__1::array<unsigned int, 256ul> const&) + 1252
6  swift                    0x00000001033dcb76 swift::serialization::Serializer::writeConformance(swift::ProtocolDecl const*, swift::ProtocolConformance const*, swift::Decl const*, std::__1::array<unsigned int, 256ul> const&, bool) + 3638
7  swift                    0x00000001033df7eb swift::serialization::Serializer::writeDecl(swift::Decl const*) + 2427
8  swift                    0x00000001033e81b5 swift::serialization::Serializer::writeAllDeclsAndTypes() + 8837
9  swift                    0x00000001033e8b1e swift::serialization::Serializer::writeAST(llvm::PointerUnion<swift::Module*, swift::SourceFile*>) + 1182
10 swift                    0x00000001033e98cb swift::serialization::Serializer::writeToStream(llvm::raw_ostream&, llvm::PointerUnion<swift::Module*, swift::SourceFile*>, swift::SILModule const*, bool, llvm::ArrayRef<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, llvm::StringRef, llvm::StringRef, bool) + 187
11 swift                    0x00000001033ea24e swift::serialize(llvm::PointerUnion<swift::Module*, swift::SourceFile*>, char const*, char const*, swift::SILModule const*, bool, llvm::ArrayRef<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, llvm::StringRef, llvm::StringRef, bool) + 398
12 swift                    0x00000001031ff679 frontend_main(llvm::ArrayRef<char const*>, char const*, void*) + 4105