enum SectionedDiffStep {
  case sectionDelete(x: Undefined)
}

abort() called

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib          0x00007fff6b42d33a __pthread_kill + 10
1   libsystem_pthread.dylib         0x00007fff6b4e9e60 pthread_kill + 430
2   libsystem_c.dylib               0x00007fff6b3b48a2 __abort + 139
3   libsystem_c.dylib               0x00007fff6b3b4817 abort + 135
4   swift                           0x00000001099d2caf swift::Mangle::Mangler::verify(llvm::StringRef) (.cold.2) + 63
5   swift                           0x000000010645273d swift::Mangle::Mangler::verify(llvm::StringRef) + 781
6   swift                           0x0000000106251509 swift::Mangle::ASTMangler::mangleAccessorEntityAsUSR(swift::AccessorKind, swift::AbstractStorageDecl const*, llvm::StringRef, bool) + 201
7   swift                           0x000000010644be5b swift::ide::printAccessorUSR(swift::AbstractStorageDecl const*, swift::AccessorKind, llvm::raw_ostream&) + 475
8   swift                           0x0000000105445350 (anonymous namespace)::IndexSwiftASTWalker::reportPseudoAccessor(swift::AbstractStorageDecl*, swift::AccessorKind, bool, swift::SourceLoc)::$_5::operator()(swift::index::IndexSymbol&) const + 768
9   swift                           0x0000000105444add (anonymous namespace)::IndexSwiftASTWalker::reportPseudoAccessor(swift::AbstractStorageDecl*, swift::AccessorKind, bool, swift::SourceLoc) + 845
10  swift                           0x0000000105441b0f (anonymous namespace)::IndexSwiftASTWalker::walkToDeclPre(swift::Decl*, swift::CharSourceRange) + 4335
11  swift                           0x0000000105439ec6 (anonymous namespace)::SemaAnnotator::walkToDeclPre(swift::Decl*) + 1638
12  swift                           0x000000010628cb2a (anonymous namespace)::Traversal::doIt(swift::Decl*) + 170
13  swift                           0x0000000106290bef swift::ASTVisitor<(anonymous namespace)::Traversal, swift::Expr*, swift::Stmt*, bool, swift::Pattern*, bool, void>::visit(swift::Decl*) + 207
14  swift                           0x000000010628cb57 (anonymous namespace)::Traversal::doIt(swift::Decl*) + 215
15  swift                           0x0000000106291879 (anonymous namespace)::Traversal::visitNominalTypeDecl(swift::NominalTypeDecl*) + 329
16  swift                           0x000000010628cb57 (anonymous namespace)::Traversal::doIt(swift::Decl*) + 215
17  swift                           0x000000010628ca6b swift::Decl::walk(swift::ASTWalker&) + 27
18  swift                           0x00000001063c6268 swift::SourceFile::walk(swift::ASTWalker&) + 216
19  swift                           0x0000000105437e6f swift::SourceEntityWalker::walk(swift::SourceFile&) + 255
20  swift                           0x0000000105440766 (anonymous namespace)::IndexSwiftASTWalker::visitModule(swift::ModuleDecl&) + 230
21  swift                           0x000000010544064c swift::index::indexSourceFile(swift::SourceFile*, swift::index::IndexDataConsumer&) + 428
22  swift                           0x00000001054468f1 recordSourceFileUnit(swift::SourceFile*, llvm::StringRef, llvm::StringRef, bool, bool, bool, llvm::StringRef, llvm::ArrayRef<clang::FileEntry const*>, clang::CompilerInstance const&, swift::DiagnosticEngine&) + 1617
23  swift                           0x0000000105446236 swift::index::indexAndRecord(swift::SourceFile*, llvm::StringRef, llvm::StringRef, bool, bool, bool, llvm::StringRef, swift::DependencyTracker const&) + 230
24  swift                           0x0000000105322c4c emitIndexDataForSourceFile(swift::SourceFile*, swift::CompilerInstance const&) + 332
25  swift                           0x0000000105322abc performEndOfPipelineActions(swift::CompilerInstance&) + 524
26  swift                           0x0000000105315351 performCompile(swift::CompilerInstance&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*) + 7761
27  swift                           0x0000000105312519 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3529
28  swift                           0x00000001052aeccd main + 861
29  libdyld.dylib                   0x00007fff6b2e5cc9 start + 1