[lldb] Add TeeLogHandler to log to 2 handlers

lldb/include/lldb/Utility/Log.h

@@ -112,6 +112,23 @@ class RotatingLogHandler : public LogHandler {
   static char ID;
 };
 
+/// A T-style log handler that multiplexes messages to two log handlers.
+class TeeLogHandler : public LogHandler {
+public:
+  TeeLogHandler(std::shared_ptr<LogHandler> first_log_handler,
+                std::shared_ptr<LogHandler> second_log_handler);
+
+  void Emit(llvm::StringRef message) override;
+
+  bool isA(const void *ClassID) const override { return ClassID == &ID; }
+  static bool classof(const LogHandler *obj) { return obj->isA(&ID); }
+
+private:
+  std::shared_ptr<LogHandler> m_first_log_handler;
+  std::shared_ptr<LogHandler> m_second_log_handler;
+  static char ID;
+};
+
 class Log final {
 public:
   /// The underlying type of all log channel enums. Declare them as:

lldb/source/Utility/Log.cpp

@@ -39,6 +39,7 @@ char LogHandler::ID;
 char StreamLogHandler::ID;
 char CallbackLogHandler::ID;
 char RotatingLogHandler::ID;
+char TeeLogHandler::ID;
 
 llvm::ManagedStatic<Log::ChannelMap> Log::g_channel_map;
 
@@ -438,3 +439,16 @@ void RotatingLogHandler::Dump(llvm::raw_ostream &stream) const {
   }
   stream.flush();
 }
+
+TeeLogHandler::TeeLogHandler(std::shared_ptr<LogHandler> first_log_handler,
+                             std::shared_ptr<LogHandler> second_log_handler)
+    : m_first_log_handler(first_log_handler),
+      m_second_log_handler(second_log_handler) {
+  assert(m_first_log_handler && "first log handler must be valid");
+  assert(m_second_log_handler && "second log handler must be valid");
+}
+
+void TeeLogHandler::Emit(llvm::StringRef message) {
+  m_first_log_handler->Emit(message);
+  m_second_log_handler->Emit(message);
+}

lldb/unittests/Utility/LogTest.cpp

@@ -200,6 +200,18 @@ TEST(LogHandlerTest, RotatingLogHandler) {
   EXPECT_EQ(GetDumpAsString(handler), "bazquxquux");
 }
 
+TEST(LogHandlerTest, TeeLogHandler) {
+  auto handler1 = std::make_shared<RotatingLogHandler>(2);
+  auto handler2 = std::make_shared<RotatingLogHandler>(2);
+  TeeLogHandler handler(handler1, handler2);
+
+  handler.Emit("foo");
+  handler.Emit("bar");
+
+  EXPECT_EQ(GetDumpAsString(*handler1), "foobar");
+  EXPECT_EQ(GetDumpAsString(*handler2), "foobar");
+}
+
 TEST_F(LogChannelTest, Enable) {
   EXPECT_EQ(nullptr, GetLog(TestChannel::FOO));
   std::string message;