Open Radar

 
Summary:


Steps to Reproduce:
1. This:
protocol FixpointType {
	typealias Algebra : AlgebraicType
	init(_ : Algebra)
	var out: Algebra { get }
}
protocol AlgebraicType {
	typealias Recur
}
enum Expr<T>: AlgebraicType {
	typealias Recur = T
	case Null // this is quite a dull language

	func map<U>(transform: T -> U) -> Expr<U> {
		return .Null
	}
}
struct Term: FixpointType {
	let out: Expr<Term>
	typealias Algebra = Expr<Term>
}


Expected Results:
should not crash


Actual Results:
but totally does:
Assertion failed: (!targetArg.empty() && "Must have a name here"), function fixAbstractFunctionNames, file /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-700.0.38.1/src/swift/lib/Sema/TypeCheckDecl.cpp, line 7174.
0  swift                    0x000000010cc53e0b llvm::sys::PrintStackTrace(__sFILE*) + 43
1  swift                    0x000000010cc5454b SignalHandler(int) + 379
2  libsystem_platform.dylib 0x00007fff88493f1a _sigtramp + 26
3  libsystem_platform.dylib 0x00007fff54f992e8 _sigtramp + 3434107880
4  libsystem_c.dylib        0x00007fff86f90b53 abort + 129
5  libsystem_c.dylib        0x00007fff86f58c39 basename + 0
6  swift                    0x000000010b2ea079 swift::TypeChecker::fixAbstractFunctionNames(swift::InFlightDiagnostic&, swift::AbstractFunctionDecl*, swift::DeclName) + 2153
7  swift                    0x000000010b31e565 std::__1::__function::__func<(anonymous namespace)::ConformanceChecker::resolveWitnessViaLookup(swift::ValueDecl*)::$_8, std::__1::allocator<(anonymous namespace)::ConformanceChecker::resolveWitnessViaLookup(swift::ValueDecl*)::$_8>, void (swift::TypeChecker&, swift::NormalProtocolConformance*)>::operator()(swift::TypeChecker&, swift::NormalProtocolConformance*&&) + 149
8  swift                    0x000000010b310c9c (anonymous namespace)::ConformanceChecker::diagnoseOrDefer(swift::ValueDecl*, bool, std::__1::function<void (swift::TypeChecker&, swift::NormalProtocolConformance*)>) + 252
9  swift                    0x000000010b31317f (anonymous namespace)::ConformanceChecker::resolveWitnessViaLookup(swift::ValueDecl*) + 2335
…
Stack dump:
0.	Program arguments: /Applications/Xcode-7-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file recur.swift -target x86_64-apple-darwin14.3.0 -enable-objc-interop -module-name recur -o /var/folders/9y/f7n4rvx901nctm_5d16c1wm40000gn/T/recur-c96d47.o 
1.	While type-checking 'Term' at recur.swift:17:1
<unknown>:0: error: unable to execute command: Abort trap: 6
<unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)



Regression:
Swift 1.2 was pretty ok with this sorta thing in general although I didn’t have the AlgebraicType protocol then so who even knows?


Notes:
This is a really productive example, I’ve hit three different new crashers trying to work around a fourth.