@available(macOS 10.12
@available(macOS 10.12
func foo() {} 

Thread 4 Crashed:: Dispatch queue: com.apple.root.default-qosThread 4 Crashed:: Dispatch queue: com.apple.root.default-qos0   libsystem_kernel.dylib         0x00007fff6b42d33a __pthread_kill + 101   libsystem_pthread.dylib        0x00007fff6b4e9e60 pthread_kill + 4302   libsystem_c.dylib              0x00007fff6b3b48a2 __abort + 1393   libsystem_c.dylib              0x00007fff6b3b4817 abort + 1354   libsystem_c.dylib              0x00007fff6b3b3ac6 __assert_rtn + 3145   com.apple.SourceKitService.5.0.20200610101_osx 0x00000001069327b3 (anonymous namespace)::ModelASTWalker::handleSpecialDeclAttribute(swift::DeclAttribute const*, llvm::ArrayRef<swift::Token>) (.cold.2) + 356   com.apple.SourceKitService.5.0.20200610101_osx 0x00000001038d4416 (anonymous namespace)::ModelASTWalker::handleSpecialDeclAttribute(swift::DeclAttribute const*, llvm::ArrayRef<swift::Token>) + 2307   com.apple.SourceKitService.5.0.20200610101_osx 0x00000001038d40e1 (anonymous namespace)::ModelASTWalker::handleAttrRanges(llvm::ArrayRef<std::__1::pair<swift::DeclAttribute const*, swift::SourceRange> >) + 6258   com.apple.SourceKitService.5.0.20200610101_osx 0x00000001038c6c1b (anonymous namespace)::ModelASTWalker::handleAttrs(swift::DeclAttributes const&) + 2839   com.apple.SourceKitService.5.0.20200610101_osx 0x00000001038c4223 (anonymous namespace)::ModelASTWalker::walkToDeclPre(swift::Decl*) + 19510  com.apple.SourceKitService.5.0.20200610101_osx 0x0000000104700b4a (anonymous namespace)::Traversal::doIt(swift::Decl*) + 17011  com.apple.SourceKitService.5.0.20200610101_osx 0x0000000104700a8b swift::Decl::walk(swift::ASTWalker&) + 2712  com.apple.SourceKitService.5.0.20200610101_osx 0x000000010482dd78 swift::SourceFile::walk(swift::ASTWalker&) + 21613  com.apple.SourceKitService.5.0.20200610101_osx 0x00000001038c22bd swift::ide::SyntaxModelContext::walk(swift::ide::SyntaxModelWalker&) + 31714  com.apple.SourceKitService.5.0.20200610101_osx 0x000000010376a0fd SourceKit::SwiftEditorDocument::readSyntaxInfo(SourceKit::EditorConsumer&) + 116515  com.apple.SourceKitService.5.0.20200610101_osx 0x000000010376eacc SourceKit::SwiftLangSupport::editorReplaceText(llvm::StringRef, llvm::MemoryBuffer*, unsigned int, unsigned int, SourceKit::EditorConsumer&) + 113216  com.apple.SourceKitService.5.0.20200610101_osx 0x00000001037add22 handleRequestImpl(void*, std::__1::function<void (void*)>) + 1445017  com.apple.SourceKitService.5.0.20200610101_osx 0x00000001037aa463 sourcekitd::handleRequest(void*, std::__1::function<void (void*)>) + 27518  com.apple.SourceKitService.5.0.20200610101_osx 0x0000000103666898 invocation function for block in sourcekitdServer_peer_event_handler(_xpc_connection_s*, void*) + 21619  libdispatch.dylib              0x00007fff6b28b6c4 _dispatch_call_block_and_release + 1220  libdispatch.dylib              0x00007fff6b28c658 _dispatch_client_callout + 821  libdispatch.dylib              0x00007fff6b28e4b0 _dispatch_queue_override_invoke + 76322  libdispatch.dylib              0x00007fff6b29a957 _dispatch_root_queue_drain + 32623  libdispatch.dylib              0x00007fff6b29b097 _dispatch_worker_thread2 + 9224  libsystem_pthread.dylib        0x00007fff6b4e69f7 _pthread_wqthread + 22025  libsystem_pthread.dylib        0x00007fff6b4e5b77 start_wqthread + 15