[lldb/Utility] Introduce UnimplementedError

This is essentially a replacement for the PacketUnimplementedError
previously present in the gdb-remote server code.

The reason I am introducing a generic error is because I wanted the
native process classes to be able to signal that they do not support
some functionality. They could not use PacketUnimplementedError as they
are independent of a specific transport protocol. Putting the error
class in the the native process code was also not ideal because the
gdb-remote code is also used for lldb-server's platform mode, which does
not (should not) know how to debug individual processes.

I'm putting it under Utility, as I think it can be generally useful for
notifying about unsupported/unimplemented functionality (and in
particular, for programatically testing whether something is
unsupported).

Differential Revision: https://reviews.llvm.org/D89121

lldb/include/lldb/Utility/UnimplementedError.h

@@ -0,0 +1,28 @@
+//===-- UnimplementedError.h ------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_UTILITY_UNIMPLEMENTEDERROR_H
+#define LLDB_UTILITY_UNIMPLEMENTEDERROR_H
+
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
+
+namespace lldb_private {
+class UnimplementedError : public llvm::ErrorInfo<UnimplementedError> {
+public:
+  static char ID;
+
+  void log(llvm::raw_ostream &OS) const override { OS << "Not implemented"; }
+
+  std::error_code convertToErrorCode() const override {
+    return llvm::errc::not_supported;
+  };
+};
+} // namespace lldb_private
+
+#endif // LLDB_UTILITY_UNIMPLEMENTEDERROR_H

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.cpp

@@ -12,11 +12,11 @@
 
 #include "GDBRemoteCommunicationServer.h"
 
-#include <cstring>
-
 #include "ProcessGDBRemoteLog.h"
 #include "lldb/Utility/StreamString.h"
 #include "lldb/Utility/StringExtractorGDBRemote.h"
+#include "lldb/Utility/UnimplementedError.h"
+#include <cstring>
 
 using namespace lldb;
 using namespace lldb_private;
@@ -113,18 +113,17 @@ GDBRemoteCommunicationServer::SendErrorResponse(const Status &error) {
 
 GDBRemoteCommunication::PacketResult
 GDBRemoteCommunicationServer::SendErrorResponse(llvm::Error error) {
+  assert(error);
   std::unique_ptr<llvm::ErrorInfoBase> EIB;
-  std::unique_ptr<PacketUnimplementedError> PUE;
+  std::unique_ptr<UnimplementedError> UE;
   llvm::handleAllErrors(
       std::move(error),
-      [&](std::unique_ptr<PacketUnimplementedError> E) { PUE = std::move(E); },
+      [&](std::unique_ptr<UnimplementedError> E) { UE = std::move(E); },
       [&](std::unique_ptr<llvm::ErrorInfoBase> E) { EIB = std::move(E); });
 
   if (EIB)
     return SendErrorResponse(Status(llvm::Error(std::move(EIB))));
-  if (PUE)
-    return SendUnimplementedResponse(PUE->message().c_str());
-  return SendErrorResponse(Status("Unknown Error"));
+  return SendUnimplementedResponse("");
 }
 
 GDBRemoteCommunication::PacketResult
@@ -152,5 +151,3 @@ GDBRemoteCommunicationServer::SendOKResponse() {
 bool GDBRemoteCommunicationServer::HandshakeWithClient() {
   return GetAck() == PacketResult::Success;
 }
-
-char PacketUnimplementedError::ID;

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.h

@@ -79,18 +79,6 @@ class GDBRemoteCommunicationServer : public GDBRemoteCommunication {
   operator=(const GDBRemoteCommunicationServer &) = delete;
 };
 
-class PacketUnimplementedError
-    : public llvm::ErrorInfo<PacketUnimplementedError, llvm::StringError> {
-public:
-  static char ID;
-  using llvm::ErrorInfo<PacketUnimplementedError,
-                        llvm::StringError>::ErrorInfo; // inherit constructors
-  PacketUnimplementedError(const llvm::Twine &S)
-      : ErrorInfo(S, llvm::errc::not_supported) {}
-
-  PacketUnimplementedError() : ErrorInfo(llvm::errc::not_supported) {}
-};
-
 } // namespace process_gdb_remote
 } // namespace lldb_private
 

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

@@ -10,13 +10,12 @@
 
 #include "lldb/Host/Config.h"
 
-#include "GDBRemoteCommunicationServerLLGS.h"
-#include "lldb/Utility/GDBRemote.h"
 
 #include <chrono>
 #include <cstring>
 #include <thread>
 
+#include "GDBRemoteCommunicationServerLLGS.h"
 #include "lldb/Host/ConnectionFileDescriptor.h"
 #include "lldb/Host/Debug.h"
 #include "lldb/Host/File.h"
@@ -32,11 +31,13 @@
 #include "lldb/Utility/Args.h"
 #include "lldb/Utility/DataBuffer.h"
 #include "lldb/Utility/Endian.h"
+#include "lldb/Utility/GDBRemote.h"
 #include "lldb/Utility/LLDBAssert.h"
 #include "lldb/Utility/Log.h"
 #include "lldb/Utility/RegisterValue.h"
 #include "lldb/Utility/State.h"
 #include "lldb/Utility/StreamString.h"
+#include "lldb/Utility/UnimplementedError.h"
 #include "lldb/Utility/UriParser.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Support/JSON.h"
@@ -2876,8 +2877,7 @@ GDBRemoteCommunicationServerLLGS::ReadXferObject(llvm::StringRef object,
   if (object == "features" && annex == "target.xml")
     return BuildTargetXml();
 
-  return llvm::make_error<PacketUnimplementedError>(
-      "Xfer object not supported");
+  return llvm::make_error<UnimplementedError>();
 }
 
 GDBRemoteCommunication::PacketResult

lldb/source/Utility/CMakeLists.txt

@@ -65,6 +65,7 @@ add_lldb_library(lldbUtility
   StructuredData.cpp
   TildeExpressionResolver.cpp
   Timer.cpp
+  UnimplementedError.cpp
   UUID.cpp
   UriParser.cpp
   UserID.cpp

lldb/source/Utility/UnimplementedError.cpp

@@ -0,0 +1,11 @@
+//===-- UnimplementedError.cpp --------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Utility/UnimplementedError.h"
+
+char lldb_private::UnimplementedError::ID;

lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationServerTest.cpp

@@ -9,9 +9,9 @@
 #include "gtest/gtest.h"
 
 #include "GDBRemoteTestUtils.h"
-
 #include "Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.h"
 #include "lldb/Utility/Connection.h"
+#include "lldb/Utility/UnimplementedError.h"
 
 namespace lldb_private {
 namespace process_gdb_remote {
@@ -39,8 +39,7 @@ TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_Status) {
 TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_UnimplementedError) {
   MockServerWithMockConnection server;
 
-  auto error =
-      llvm::make_error<PacketUnimplementedError>("Test unimplemented error");
+  auto error = llvm::make_error<UnimplementedError>();
   server.SendErrorResponse(std::move(error));
 
   EXPECT_THAT(server.GetPackets(), testing::ElementsAre("$#00"));
@@ -61,8 +60,8 @@ TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_StringError) {
 TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_ErrorList) {
   MockServerWithMockConnection server;
 
-  auto error = llvm::joinErrors(llvm::make_error<PacketUnimplementedError>(),
-                                llvm::make_error<PacketUnimplementedError>());
+  auto error = llvm::joinErrors(llvm::make_error<UnimplementedError>(),
+                                llvm::make_error<UnimplementedError>());
 
   server.SendErrorResponse(std::move(error));
   // Make sure only one packet is sent even when there are multiple errors.