recursivelyAllWritableKeyPaths crash in specific case

[ematejska]

Imported from JIRA https://bugs.swift.org/browse/TF-1207

Type:	Bug	Priority:	Minor
Reporter:	Takehiro Araki	Assignee:	Unassigned
Resolution:	Unresolved	Votes:	0
Labels:	None
Environment:	swift-tensorflow-RELEASE-0.8.xctoolchain

If the target type has both Scalar parameter and Activation parameter, recursivelyAllWritableKeyPaths crash.

struct Model<Scalar: FloatingPoint&Differentiable>: KeyPathIterable {
    let scale: Scalar = 0
    let activation: Activation = { $0 }
    typealias Activation = @differentiable (Scalar) -> Scalar
}

let model = Model<Float>()
for kp in model.recursivelyAllWritableKeyPaths(to: Float.self) {
    print(model[keyPath: kp])
}

Stack dump:
0.	Program arguments: /Library/Developer/Toolchains/swift-tensorflow-RELEASE-0.8.xctoolchain/usr/bin/swift -frontend -interpret main.swift -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -color-diagnostics -module-name main 
1.	Swift version 5.2-dev (LLVM b3057cffb6, Swift da7410955d)
2.	While running user code "main.swift"
0  swift                    0x0000000112971e75 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift                    0x00000001129710b5 llvm::sys::RunSignalHandlers() + 85
2  swift                    0x000000011297245c SignalHandler(int) + 268
3  libsystem_platform.dylib 0x00007fff781b5b5d _sigtramp + 29
4  libsystem_platform.dylib 0x00000000000004b8 _sigtramp + 18446603338501106040
5  libswiftCore.dylib       0x000000011a97c059 $ss15KeyPathIterablePsE014recursivelyAllA5PathsSays07PartialaB0CyxGGvg + 1017
6  libswiftCore.dylib       0x000000011a97d602 $ss15KeyPathIterablePsE014recursivelyAllA5Paths2toSays0aB0Cyxqd__GGqd__m_tlF + 34
7  libswiftCore.dylib       0x000000011a97d91a $ss15KeyPathIterablePsE011allWritableA5Paths2toSays0eaB0Cyxqd__GGqd__m_tlFTm + 26
8  libswiftCore.dylib       0x000000011b0070ed $ss15KeyPathIterablePsE011allWritableA5Paths2toSays0eaB0Cyxqd__GGqd__m_tlFTm + 6854637
9  swift                    0x000000010e8d5a58 llvm::MCJIT::runFunction(llvm::Function*, llvm::ArrayRef<llvm::GenericValue>) + 456
10 swift                    0x000000010e8d8bf1 llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, char const* const*) + 1297
11 swift                    0x000000010e8cbbdf swift::RunImmediately(swift::CompilerInstance&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, swift::IRGenOptions const&, swift::SILOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >&&) + 3471
12 swift                    0x000000010e8b494a performCompileStepsPostSILGen(swift::CompilerInstance&, swift::CompilerInvocation const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, bool, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, swift::PrimarySpecificPaths const&, bool, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 2378
13 swift                    0x000000010e8a9363 performCompile(swift::CompilerInstance&, swift::CompilerInvocation const&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 9299
14 swift                    0x000000010e8a5f48 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 4472
15 swift                    0x000000010e83887d main + 861
16 libdyld.dylib            0x00007fff77fca3d5 start + 1
17 libdyld.dylib            0x000000000000000a start + 18446603338503117878
Segmentation fault: 11