Building a function signature with parameter names using Clang.cpp

/// Build a function signature.
static std::string get_function_signature(IndexFile* db,
                                          const CXIdxDeclInfo* decl) {
  // Build the function name, with scope and parameters
  std::string returnType;
  if (decl->entityInfo->kind != CXCursor_Constructor &&
      decl->entityInfo->kind != CXCursor_Destructor) {
    returnType = ::ToString(
        clang_getTypeSpelling(clang_getCursorResultType(decl->cursor)));
  }
  std::string signature{returnType};
  signature.append(" ");

  auto container = decl->semanticContainer;
  if (IsTypeDefinition(container)) {
    IndexTypeId declaring_type_id = db->ToTypeId(container->cursor);
    IndexType* declaring_type_def = db->Resolve(declaring_type_id);
    auto container_name = declaring_type_def->def.detailed_name;
    signature.append(container_name);
    signature.append("::");
  }

  auto functionName = ::ToString(clang_getCursorSpelling(decl->cursor));
  auto pos = functionName.find("<", 0);
  if (pos != std::string::npos) {
    functionName = functionName.substr(0, pos);
  }
  signature.append(functionName);

  std::string parameter_types = "";
  // Add the parameters declarations including their names.
  parameter_types.append("(");
  int numArgs = clang_Cursor_getNumArguments(decl->cursor);
  for (int i = 0; i < numArgs; i++) {
    CXCursor arg = clang_Cursor_getArgument(decl->cursor, i);
    auto id = ::ToString(clang_getCursorDisplayName(arg));
    auto type = ::ToString(clang_getTypeSpelling(clang_getCursorType(arg)));
    parameter_types.append(type + ' ' + id + (i < numArgs - 1 ? ", " : ""));
  }

  if (clang_Cursor_isVariadic(decl->cursor)) {
    parameter_types.append(numArgs > 0 ? ", ..." : "...");
  }

  parameter_types.append(")");
  signature.append(parameter_types);
  return signature;
}