Open Radar

 
Summary:
More infinite loopage.

Steps to Reproduce:
1. This code:
protocol FixpointType: _FixpointType {
	typealias Algebra : AlgebraicType
}

protocol _FixpointType {
	typealias Algebra
	init(_ : Algebra)
	var out: Algebra { get }
}

protocol AlgebraicType {
	typealias Recur : _FixpointType
}

enum Expr<T: FixpointType>: AlgebraicType {
	typealias Recur = T
	case Null
	func map<U>(transform: T -> U) -> Expr<U> { return .Null }
}

func out<Fix: FixpointType>(v: Fix) -> Fix.Algebra { return v.out }

func cata<T, Fix: FixpointType where Fix.Algebra == Expr<Fix>>(f: Expr<T> -> T)(_ term: Fix) -> T {
	return f({ $0.map(cata(f)) }(out(term)))
}

Expected Results:
should not infinite loop and crash swiftc

Actual Results:
but totally does:
rob@Resonance ~/Desktop> swiftc -v boom.swift
Apple Swift version 2.0 (swiftlang-700.0.47.4 clang-700.0.59.1)
Target: x86_64-apple-darwin14.4.0
/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file boom.swift -target x86_64-apple-darwin14.4.0 -enable-objc-interop -color-diagnostics -module-name boom -o /var/folders/9y/f7n4rvx901nctm_5d16c1wm40000gn/T/boom-d6304d.o
<unknown>:0: error: unable to execute command: Segmentation fault: 11
<unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)

509 swift                         	0x000000010ebc2ee3 swift::TypeBase::gatherAllSubstitutions(swift::ModuleDecl*, llvm::SmallVectorImpl<swift::Substitution>&, swift::LazyResolver*, swift::DeclContext*) + 211
510 swift                         	0x000000010eb94ca6 swift::ModuleDecl::lookupConformance(swift::Type, swift::ProtocolDecl*, swift::LazyResolver*) + 1958
511 swift                         	0x000000010eb93f66 swift::BoundGenericType::getSubstitutions(swift::ModuleDecl*, swift::LazyResolver*, swift::DeclContext*) + 1606


Regression:
N/A

Notes:
N/A