Fix MSVC build issues

MSVC fails when there is ambiguity (multiple options) around implicit
type conversion operators.

Make ConstString's conversion operator to string_view explicit to
avoid ambiguity with one to StringRef and remove an unused local
variable that MSVC also fails on.

Cherrypick commit llvm@34a0f37

Author: hjyamauchi

lldb/include/lldb/Utility/ConstString.h

@@ -184,8 +184,8 @@ class ConstString {
   // Implicitly convert \class ConstString instances to \class StringRef.
   operator llvm::StringRef() const { return GetStringRef(); }
 
-  // Implicitly convert \class ConstString instances to \class std::string_view.
-  operator std::string_view() const {
+  // Explicitly convert \class ConstString instances to \class std::string_view.
+  explicit operator std::string_view() const {
     return std::string_view(m_string, GetLength());
   }
 
@@ -435,6 +435,11 @@ class ConstString {
 /// Stream the string value \a str to the stream \a s
 Stream &operator<<(Stream &s, ConstString str);
 
+inline std::string &operator+=(std::string &str, const lldb_private::ConstString &s) {
+  str += llvm::StringRef(s).str();
+  return str;
+}
+
 } // namespace lldb_private
 
 namespace llvm {

lldb/source/Core/Mangled.cpp

@@ -138,7 +138,7 @@ void Mangled::SetValue(ConstString name) {
 }
 
 // Local helpers for different demangling implementations.
-static char *GetMSVCDemangledStr(std::string_view M) {
+static char *GetMSVCDemangledStr(llvm::StringRef M) {
   char *demangled_cstr = llvm::microsoftDemangle(
       M, nullptr, nullptr,
       llvm::MSDemangleFlags(
@@ -182,27 +182,29 @@ static char *GetItaniumDemangledStr(const char *M) {
   return demangled_cstr;
 }
 
-static char *GetRustV0DemangledStr(std::string_view M) {
+static char *GetRustV0DemangledStr(llvm::StringRef M) {
   char *demangled_cstr = llvm::rustDemangle(M);
 
   if (Log *log = GetLog(LLDBLog::Demangle)) {
     if (demangled_cstr && demangled_cstr[0])
       LLDB_LOG(log, "demangled rustv0: {0} -> \"{1}\"", M, demangled_cstr);
     else
-      LLDB_LOG(log, "demangled rustv0: {0} -> error: failed to demangle", M);
+      LLDB_LOG(log, "demangled rustv0: {0} -> error: failed to demangle",
+               static_cast<std::string_view>(M));
   }
 
   return demangled_cstr;
 }
 
-static char *GetDLangDemangledStr(std::string_view M) {
+static char *GetDLangDemangledStr(llvm::StringRef M) {
   char *demangled_cstr = llvm::dlangDemangle(M);
 
   if (Log *log = GetLog(LLDBLog::Demangle)) {
     if (demangled_cstr && demangled_cstr[0])
       LLDB_LOG(log, "demangled dlang: {0} -> \"{1}\"", M, demangled_cstr);
     else
-      LLDB_LOG(log, "demangled dlang: {0} -> error: failed to demangle", M);
+      LLDB_LOG(log, "demangled dlang: {0} -> error: failed to demangle",
+               static_cast<std::string_view>(M));
   }
 
   return demangled_cstr;

lldb/unittests/SymbolFile/PDB/SymbolFilePDBTests.cpp

@@ -528,7 +528,6 @@ TEST_F(SymbolFilePDBTests, TestTypedefs) {
   SymbolFilePDB *symfile =
       static_cast<SymbolFilePDB *>(module->GetSymbolFile());
   llvm::pdb::IPDBSession &session = symfile->GetPDBSession();
-  TypeMap results;
 
   const char *TypedefsToCheck[] = {"ClassTypedef", "NSClassTypedef",
                                    "FuncPointerTypedef",