Michael G, is this related to your adoption of StringSwitch?
/home/buildnode/jenkins/workspace/oss-swift-4.2-incremental-RA-linux-ubuntu-16_04/swift/lib/RemoteAST/RemoteAST.cpp:590:13: error: no viable conversion from 'const char [4]' to 'llvm::StringLiteral' **13:57:49** .Case(MANGLING_MODULE_OBJC, ForeignModuleKind::Imported) **13:57:49** ^~~~~~~~~~~~~~~~~~~~ **13:57:49** /home/buildnode/jenkins/workspace/oss-swift-4.2-incremental-RA-linux-ubuntu-16_04/llvm/include/llvm/ADT/StringRef.h:857:9: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'const char [4]' to 'const llvm::StringLiteral &' for 1st argument **13:57:49** class StringLiteral : public StringRef { **13:57:49** ^ **13:57:49** /home/buildnode/jenkins/workspace/oss-swift-4.2-incremental-RA-linux-ubuntu-16_04/llvm/include/llvm/ADT/StringRef.h:857:9: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'const char [4]' to 'llvm::StringLiteral &&' for 1st argument **13:57:49** /home/buildnode/jenkins/workspace/oss-swift-4.2-incremental-RA-linux-ubuntu-16_04/llvm/include/llvm/ADT/StringRef.h:864:15: note: candidate disabled: invalid string literal **13:57:49** constexpr StringLiteral(const char (&Str)[N]) **13:57:49** ^ **13:57:49** /home/buildnode/jenkins/workspace/oss-swift-4.2-incremental-RA-linux-ubuntu-16_04/llvm/include/llvm/ADT/StringSwitch.h:70:36: note: passing argument to parameter 'S' here **13:57:49** StringSwitch &Case(StringLiteral S, T Value) { **13:57:49** ^ **13:57:49** 1 warning and 1 error generated.