[lldb] Report debugger diagnostics as events

[JDevlieghere]

Summary

Report warnings and errors through events instead of printing directly the to the debugger's error stream. Diagnostic events are handled by the default event loop. This allows IDEs such as Xcode to report these issues in the UI instead of having them show up in the debugger console.

[JDevlieghere]

Use the asynchronous error stream

[labath]

It seems to me that it would be better to decentralize the warning tracking. Also due to a central list of all possible warnings not being modular, but mainly because I can imagine that some warnings may want to be reported with different "scopes" -- once per target, thread, module (this is the case of the "dwp missing" warning) or whatever. That won't work if the list is managed centrally in the debugger object. We could define some token warn_once type (maybe just a typedef to once_flag or atomic_flag) that would have to be passed to the warning emitting function. The function would handle the actual "once" logic, and the scope of the token variable would determine the frequency of the warning.

My second remark is that this does not help with the warnings that are not tied to a specific debugger instance -- such as those coming from the module parsing code. I don't know if you have a need to display those (I know I don't), but it may be nice to set things up so that we're able to transmit those as well -- I believe we are able to do that for progress events.

lldb/include/lldb/Core/DebuggerEvents.h

91

[JDevlieghere]

Address code review:

• Decentralize tracking whether a warning/error has been emitted.
• Support diagnostics that are not tied to a single debugger.

[labath]

Heh, I didn't realize that "debugger-less" events are implemented by iterating over all debugger instances, but since we're doing that for progress events anyway, we might as well copy the pattern.

Any chance of a test case for some of this stuff? Maybe a unittest which creates a Debugger object and uses it to send/receive some events?

lldb/include/lldb/Core/DebuggerEvents.h

73

Do we really need separate types for this? The handling of the two events is completely identical (except for the "error"/"warning" prefix, so it seems that an enum would suffice. The classes won't make it to the SB api (I think), so it's not like we're locking ourselves into a particular design.

lldb/source/Core/Debugger.cpp

1680–1684

StartListeningForEvents(eBroadcastBitProgress | eBroadcastBitWarning | eBroadcastBitError) ?

1879

GetAsyncErrorStream returns a (shared -- it should probably be a unique_ptr instead) pointer to a new object. You can't just throw it away here.

[JDevlieghere]

Address code review feedback

[JDevlieghere]

Print diagnostics directly to the debugger's error stream if nobody is listening for them.

[JDevlieghere]

Migrate a few more call sites to Debugger::Report{Error,Warning}

[labath]

cool

lldb/unittests/Core/DiagnosticEventTest.cpp

54–55

I guess you could move this into the SetUp function as well.

lldb/include/lldb/Core/Debugger.h

 //===-- Debugger.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_CORE_DEBUGGER_H
 #define LLDB_CORE_DEBUGGER_H
 
 #include <cstdint>
 
 #include <memory>
 #include <vector>
 
+#include "lldb/Core/DebuggerEvents.h"
 #include "lldb/Core/FormatEntity.h"
 #include "lldb/Core/IOHandler.h"
 #include "lldb/Core/SourceManager.h"
 #include "lldb/Core/StreamFile.h"
 #include "lldb/Core/UserSettingsController.h"
 #include "lldb/Host/HostThread.h"
 #include "lldb/Host/Terminal.h"
 #include "lldb/Target/ExecutionContext.h"

 
 namespace lldb_private {
 class Address;
 class CommandInterpreter;
 class Process;
 class Stream;
 class SymbolContext;
 class Target;
-class ProgressEventData;
 
 namespace repro {
 class DataRecorder;
 }
 
 /// \class Debugger Debugger.h "lldb/Core/Debugger.h"
 /// A class to manage flag bits.
 ///
 /// Provides a global root objects for the debugger core.
 
 class Debugger : public std::enable_shared_from_this<Debugger>,
                  public UserID,
                  public Properties {
   friend class SourceManager; // For GetSourceFileCache.
 
 public:
   /// Broadcaster event bits definitions.
   enum {
     eBroadcastBitProgress = (1 << 0),
+    eBroadcastBitWarning = (1 << 1),
+    eBroadcastBitError = (1 << 2),
   };
 
   static ConstString GetStaticBroadcasterClass();
 
   /// Get the public broadcaster for this debugger.
   Broadcaster &GetBroadcaster() { return m_broadcaster; }
   const Broadcaster &GetBroadcaster() const { return m_broadcaster; }
 
public:
   // target with entities that will be copied over to new targets.
   Target &GetSelectedOrDummyTarget(bool prefer_dummy = false);
   Target &GetDummyTarget() { return *m_dummy_target_sp; }
 
   lldb::BroadcasterManagerSP GetBroadcasterManager() {
     return m_broadcaster_manager_sp;
   }
 
+  /// Report warning events.
+  ///
+  /// Progress events will be delivered to any debuggers that have listeners
+  /// for the eBroadcastBitError.
+  ///
+  /// \param[in] message
+  ///   The warning message to be reported.
+  ///
+  /// \param [in] debugger_id
+  ///   If this optional parameter has a value, it indicates the unique
+  ///   debugger identifier that this progress should be delivered to. If this
+  ///   optional parameter does not have a value, the progress will be
+  ///   delivered to all debuggers.
+  ///
+  /// \param [in] once
+  ///   If a pointer is passed to a std::once_flag, then it will be used to
+  ///   ensure the given warning is only broadcast once.
+  static void
+  ReportWarning(std::string messsage,
+                llvm::Optional<lldb::user_id_t> debugger_id = llvm::None,
+                std::once_flag *once = nullptr);
+
+  /// Report error events.
+  ///
+  /// Progress events will be delivered to any debuggers that have listeners
+  /// for the eBroadcastBitError.
+  ///
+  /// \param[in] message
+  ///   The error message to be reported.
+  ///
+  /// \param [in] debugger_id
+  ///   If this optional parameter has a value, it indicates the unique
+  ///   debugger identifier that this progress should be delivered to. If this
+  ///   optional parameter does not have a value, the progress will be
+  ///   delivered to all debuggers.
+  ///
+  /// \param [in] once
+  ///   If a pointer is passed to a std::once_flag, then it will be used to
+  ///   ensure the given error is only broadcast once.
+  static void
+  ReportError(std::string messsage,
+              llvm::Optional<lldb::user_id_t> debugger_id = llvm::None,
+              std::once_flag *once = nullptr);
+
 protected:
   friend class CommandInterpreter;
   friend class REPL;
   friend class Progress;
 
   /// Report progress events.
   ///
   /// Progress events will be delivered to any debuggers that have listeners
protected:
   ///   If this optional parameter has a value, it indicates the unique
   ///   debugger identifier that this progress should be delivered to. If this
   ///   optional parameter does not have a value, the progress will be
   ///   delivered to all debuggers.
   static void ReportProgress(uint64_t progress_id, const std::string &message,
                              uint64_t completed, uint64_t total,
                              llvm::Optional<lldb::user_id_t> debugger_id);
 
+  static void ReportDiagnosticImpl(DiagnosticEventData::Type type,
+                                   std::string message,
+                                   llvm::Optional<lldb::user_id_t> debugger_id,
+                                   std::once_flag *once);
+
   void PrintProgress(const ProgressEventData &data);
 
   bool StartEventHandlerThread();
 
   void StopEventHandlerThread();
 
   void PushIOHandler(const lldb::IOHandlerSP &reader_sp,
                      bool cancel_top_handler = true);
protected:
   void HandleBreakpointEvent(const lldb::EventSP &event_sp);
 
   void HandleProcessEvent(const lldb::EventSP &event_sp);
 
   void HandleThreadEvent(const lldb::EventSP &event_sp);
 
   void HandleProgressEvent(const lldb::EventSP &event_sp);
 
+  void HandleDiagnosticEvent(const lldb::EventSP &event_sp);
+
   // Ensures two threads don't attempt to flush process output in parallel.
   std::mutex m_output_flush_mutex;
   void FlushProcessOutput(Process &process, bool flush_stdout,
                           bool flush_stderr);
 
   SourceManager::SourceFileCache &GetSourceFileCache() {
     return m_source_file_cache;
   }

lldb/include/lldb/Core/DebuggerEvents.h

private:
   std::string m_message;
   const uint64_t m_id;
   uint64_t m_completed;
   const uint64_t m_total;
   const bool m_debugger_specific;
   ProgressEventData(const ProgressEventData &) = delete;
   const ProgressEventData &operator=(const ProgressEventData &) = delete;
 };
+
+class DiagnosticEventData : public EventData {
+public:
+  enum class Type {
+    Warning,
+    Error,
+  };
+  DiagnosticEventData(Type type, std::string message, bool debugger_specific)
+      : m_message(std::move(message)), m_type(type),
+        m_debugger_specific(debugger_specific) {}
+  ~DiagnosticEventData() {}
+
+  const std::string &GetMessage() const { return m_message; }
+  Type GetType() const { return m_type; }
+
+  llvm::StringRef GetPrefix() const;
+
+  void Dump(Stream *s) const override;
+
+  static ConstString GetFlavorString();
+  ConstString GetFlavor() const override;
+
+  static const DiagnosticEventData *
+  GetEventDataFromEvent(const Event *event_ptr);
+
+protected:
+  std::string m_message;
+  Type m_type;
+  const bool m_debugger_specific;
+
+  DiagnosticEventData(const DiagnosticEventData &) = delete;
+  const DiagnosticEventData &operator=(const DiagnosticEventData &) = delete;
+};
+
 } // namespace lldb_private
 
 #endif // LLDB_CORE_DEBUGGER_EVENTS_H

lldb/source/Core/Debugger.cpp

     std::lock_guard<std::recursive_mutex> guard(*g_debugger_list_mutex_ptr);
     DebuggerList::iterator pos, end = g_debugger_list_ptr->end();
     for (pos = g_debugger_list_ptr->begin(); pos != end; ++pos)
       PrivateReportProgress(*(*pos), progress_id, message, completed, total,
                             /*is_debugger_specific*/ false);
   }
 }
 
+static void PrivateReportDiagnostic(Debugger &debugger,
+                                    DiagnosticEventData::Type type,
+                                    std::string message,
+                                    bool debugger_specific) {
+  uint32_t event_type = 0;
+  switch (type) {
+  case DiagnosticEventData::Type::Warning:
+    event_type = Debugger::eBroadcastBitWarning;
+    break;
+  case DiagnosticEventData::Type::Error:
+    event_type = Debugger::eBroadcastBitError;
+    break;
+  }
+
+  Broadcaster &broadcaster = debugger.GetBroadcaster();
+  if (!broadcaster.EventTypeHasListeners(event_type)) {
+    // Diagnostics are too important to drop. If nobody is listening, print the
+    // diagnostic directly to the debugger's error stream.
+    DiagnosticEventData event_data(type, std::move(message), debugger_specific);
+    StreamSP stream = debugger.GetAsyncErrorStream();
+    event_data.Dump(stream.get());
+    return;
+  }
+  EventSP event_sp = std::make_shared<Event>(
+      event_type,
+      new DiagnosticEventData(type, std::move(message), debugger_specific));
+  broadcaster.BroadcastEvent(event_sp);
+}
+
+void Debugger::ReportDiagnosticImpl(DiagnosticEventData::Type type,
+                                    std::string message,
+                                    llvm::Optional<lldb::user_id_t> debugger_id,
+                                    std::once_flag *once) {
+  auto ReportDiagnosticLambda = [&]() {
+    // Check if this progress is for a specific debugger.
+    if (debugger_id) {
+      // It is debugger specific, grab it and deliver the event if the debugger
+      // still exists.
+      DebuggerSP debugger_sp = FindDebuggerWithID(*debugger_id);
+      if (debugger_sp)
+        PrivateReportDiagnostic(*debugger_sp, type, std::move(message), true);
+      return;
+    }
+    // The progress event is not debugger specific, iterate over all debuggers
+    // and deliver a progress event to each one.
+    if (g_debugger_list_ptr && g_debugger_list_mutex_ptr) {
+      std::lock_guard<std::recursive_mutex> guard(*g_debugger_list_mutex_ptr);
+      for (const auto &debugger : *g_debugger_list_ptr)
+        PrivateReportDiagnostic(*debugger, type, message, false);
+    }
+  };
+
+  if (once)
+    std::call_once(*once, ReportDiagnosticLambda);
+  else
+    ReportDiagnosticLambda();
+}
+
+void Debugger::ReportWarning(std::string message,
+                             llvm::Optional<lldb::user_id_t> debugger_id,
+                             std::once_flag *once) {
+  ReportDiagnosticImpl(DiagnosticEventData::Type::Warning, std::move(message),
+                       debugger_id, once);
+}
+
+void Debugger::ReportError(std::string message,
+                           llvm::Optional<lldb::user_id_t> debugger_id,
+                           std::once_flag *once) {
+
+  ReportDiagnosticImpl(DiagnosticEventData::Type::Error, std::move(message),
+                       debugger_id, once);
+}
+
 bool Debugger::EnableLog(llvm::StringRef channel,
                          llvm::ArrayRef<const char *> categories,
                          llvm::StringRef log_file, uint32_t log_options,
                          llvm::raw_ostream &error_stream) {
   const bool should_close = true;
   const bool unbuffered = true;
 
   std::shared_ptr<llvm::raw_ostream> log_stream_sp;

                                           process_event_spec);
   listener_sp->StartListeningForEventSpec(m_broadcaster_manager_sp,
                                           thread_event_spec);
   listener_sp->StartListeningForEvents(
       m_command_interpreter_up.get(),
       CommandInterpreter::eBroadcastBitQuitCommandReceived |
           CommandInterpreter::eBroadcastBitAsynchronousOutputData |
           CommandInterpreter::eBroadcastBitAsynchronousErrorData);
 
-  listener_sp->StartListeningForEvents(&m_broadcaster,
-                                       Debugger::eBroadcastBitProgress);
+  listener_sp->StartListeningForEvents(
+      &m_broadcaster,
+      eBroadcastBitProgress | eBroadcastBitWarning | eBroadcastBitError);
 
   // Let the thread that spawned us know that we have started up and that we
   // are now listening to all required events so no events get missed
   m_sync_broadcaster.BroadcastEvent(eBroadcastBitEventThreadIsListening);
 
   bool done = false;
   while (!done) {
     EventSP event_sp;
     if (listener_sp->GetEvent(event_sp, llvm::None)) {

                   output_sp->PutCString(data);
                   output_sp->Flush();
                 }
               }
             }
           } else if (broadcaster == &m_broadcaster) {
             if (event_type & Debugger::eBroadcastBitProgress)
               HandleProgressEvent(event_sp);
+            else if (event_type & Debugger::eBroadcastBitWarning)
+              HandleDiagnosticEvent(event_sp);
+            else if (event_type & Debugger::eBroadcastBitError)
+              HandleDiagnosticEvent(event_sp);
           }
         }
 
         if (m_forward_listener_sp)
           m_forward_listener_sp->AddEvent(event_sp);
       }
     }
   }

 
   // Clear until the end of the line.
   output->Printf("\x1B[K\r");
 
   // Flush the output.
   output->Flush();
 }
 
+void Debugger::HandleDiagnosticEvent(const lldb::EventSP &event_sp) {
+  auto *data = DiagnosticEventData::GetEventDataFromEvent(event_sp.get());
+  if (!data)
+    return;
+
+  StreamSP stream = GetAsyncErrorStream();
+  data->Dump(stream.get());
+}
+
 bool Debugger::HasIOHandlerThread() { return m_io_handler_thread.IsJoinable(); }
 
 bool Debugger::StartIOHandlerThread() {
   if (!m_io_handler_thread.IsJoinable()) {
     llvm::Expected<HostThread> io_handler_thread = ThreadLauncher::LaunchThread(
         "lldb.debugger.io-handler", [this] { return IOHandlerThread(); },
         8 * 1024 * 1024); // Use larger 8MB stack for this thread
     if (io_handler_thread) {

lldb/source/Core/DebuggerEvents.cpp

 //===-- DebuggerEvents.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/Core/DebuggerEvents.h"
 
 using namespace lldb_private;
 
+template <typename T>
+static const T *GetEventDataFromEventImpl(const Event *event_ptr) {
+  if (event_ptr)
+    if (const EventData *event_data = event_ptr->GetData())
+      if (event_data->GetFlavor() == T::GetFlavorString())
+        return static_cast<const T *>(event_ptr->GetData());
+  return nullptr;
+}
+
 ConstString ProgressEventData::GetFlavorString() {
   static ConstString g_flavor("ProgressEventData");
   return g_flavor;
 }
 
 ConstString ProgressEventData::GetFlavor() const {
   return ProgressEventData::GetFlavorString();
 }
 
 void ProgressEventData::Dump(Stream *s) const {
   s->Printf(" id = %" PRIu64 ", message = \"%s\"", m_id, m_message.c_str());
   if (m_completed == 0 || m_completed == m_total)
     s->Printf(", type = %s", m_completed == 0 ? "start" : "end");
   else
     s->PutCString(", type = update");
   // If m_total is UINT64_MAX, there is no progress to report, just "start"
   // and "end". If it isn't we will show the completed and total amounts.
   if (m_total != UINT64_MAX)
     s->Printf(", progress = %" PRIu64 " of %" PRIu64, m_completed, m_total);
 }
 
 const ProgressEventData *
 ProgressEventData::GetEventDataFromEvent(const Event *event_ptr) {
-  if (event_ptr)
-    if (const EventData *event_data = event_ptr->GetData())
-      if (event_data->GetFlavor() == ProgressEventData::GetFlavorString())
-        return static_cast<const ProgressEventData *>(event_ptr->GetData());
-  return nullptr;
+  return GetEventDataFromEventImpl<ProgressEventData>(event_ptr);
+}
+
+llvm::StringRef DiagnosticEventData::GetPrefix() const {
+  switch (m_type) {
+  case Type::Warning:
+    return "warning";
+  case Type::Error:
+    return "error";
+  }
+}
+
+void DiagnosticEventData::Dump(Stream *s) const {
+  *s << GetPrefix() << ": " << GetMessage() << '\n';
+  s->Flush();
+}
+
+ConstString DiagnosticEventData::GetFlavorString() {
+  static ConstString g_flavor("DiagnosticEventData");
+  return g_flavor;
+}
+
+ConstString DiagnosticEventData::GetFlavor() const {
+  return DiagnosticEventData::GetFlavorString();
+}
+
+const DiagnosticEventData *
+DiagnosticEventData::GetEventDataFromEvent(const Event *event_ptr) {
+  return GetEventDataFromEventImpl<DiagnosticEventData>(event_ptr);
 }

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.h

private:
   lldb::addr_t m_relative_selector_base;
   HashTableSignature m_hash_signature;
   bool m_has_object_getClass;
   bool m_has_objc_copyRealizedClassList;
   bool m_loaded_objc_opt;
   std::unique_ptr<NonPointerISACache> m_non_pointer_isa_cache_up;
   std::unique_ptr<TaggedPointerVendor> m_tagged_pointer_vendor_up;
   EncodingToTypeSP m_encoding_to_type_sp;
-  bool m_noclasses_warning_emitted;
+  std::once_flag m_no_classes_cached_warning;
+  std::once_flag m_no_expanded_cache_warning;
   llvm::Optional<std::pair<lldb::addr_t, lldb::addr_t>> m_CFBoolean_values;
   uint64_t m_realized_class_generation_count;
 };
 
 } // namespace lldb_private
 
 #endif // LLDB_SOURCE_PLUGINS_LANGUAGERUNTIME_OBJC_APPLEOBJCRUNTIME_APPLEOBJCRUNTIMEV2_H

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

 #include "clang/AST/DeclObjC.h"
 
 #include "lldb/Host/OptionParser.h"
 #include "lldb/Symbol/CompilerType.h"
 #include "lldb/lldb-enumerations.h"
 
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "lldb/Core/Debugger.h"
+#include "lldb/Core/DebuggerEvents.h"
 #include "lldb/Core/Module.h"
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Core/Section.h"
 #include "lldb/Core/ValueObjectConstResult.h"
 #include "lldb/Core/ValueObjectVariable.h"
 #include "lldb/Expression/DiagnosticManager.h"
 #include "lldb/Expression/FunctionCaller.h"
 #include "lldb/Expression/UtilityFunction.h"
: AppleObjCRuntime(process), m_objc_module_sp(objc_module_sp),
       m_shared_cache_class_info_extractor(*this), m_decl_vendor_up(),
       m_tagged_pointer_obfuscator(LLDB_INVALID_ADDRESS),
       m_isa_hash_table_ptr(LLDB_INVALID_ADDRESS),
       m_relative_selector_base(LLDB_INVALID_ADDRESS), m_hash_signature(),
       m_has_object_getClass(false), m_has_objc_copyRealizedClassList(false),
       m_loaded_objc_opt(false), m_non_pointer_isa_cache_up(),
       m_tagged_pointer_vendor_up(
           TaggedPointerVendorV2::CreateInstance(*this, objc_module_sp)),
-      m_encoding_to_type_sp(), m_noclasses_warning_emitted(false),
-      m_CFBoolean_values(), m_realized_class_generation_count(0) {
+      m_encoding_to_type_sp(), m_CFBoolean_values(),
+      m_realized_class_generation_count(0) {
   static const ConstString g_gdb_object_getClass("gdb_object_getClass");
   m_has_object_getClass = HasSymbol(g_gdb_object_getClass);
   static const ConstString g_objc_copyRealizedClassList(
       "_ZL33objc_copyRealizedClassList_nolockPj");
   m_has_objc_copyRealizedClassList = HasSymbol(g_objc_copyRealizedClassList);
   WarnIfNoExpandedSharedCache();
   RegisterObjCExceptionRecognizer(process);
 }
static bool DoesProcessHaveSharedCache(Process &process) {
   if (platform_plugin_name_sr.endswith("-simulator"))
     return false;
 
   return true;
 }
 
 void AppleObjCRuntimeV2::WarnIfNoClassesCached(
     SharedCacheWarningReason reason) {
-  if (m_noclasses_warning_emitted)
-    return;
-
   if (GetProcess() && !DoesProcessHaveSharedCache(*GetProcess())) {
     // Simulators do not have the objc_opt_ro class table so don't actually
     // complain to the user
-    m_noclasses_warning_emitted = true;
     return;
   }
 
   Debugger &debugger(GetProcess()->GetTarget().GetDebugger());
-  if (auto stream = debugger.GetAsyncOutputStream()) {
-    switch (reason) {
-    case SharedCacheWarningReason::eNotEnoughClassesRead:
-      stream->PutCString("warning: could not find Objective-C class data in "
+    Debugger::ReportWarning("warning: could not find Objective-C class data in "
                             "the process. This may reduce the quality of type "
-                         "information available.\n");
-      m_noclasses_warning_emitted = true;
-      break;
-    case SharedCacheWarningReason::eExpressionExecutionFailure:
-      stream->PutCString("warning: could not execute support code to read "
-                         "Objective-C class data in the process. This may "
-                         "reduce the quality of type information available.\n");
-      m_noclasses_warning_emitted = true;
-      break;
-    }
-  }
-}
+                            "information available.\n",
+                            debugger.GetID(), &m_no_classes_cached_warning);
+    Debugger::ReportWarning(
+        "warning: could not execute support code to read "
+        "reduce the quality of type information available.\n",
+        debugger.GetID(), &m_no_classes_cached_warning);
 
 void AppleObjCRuntimeV2::WarnIfNoExpandedSharedCache() {
   if (!m_objc_module_sp)
     return;
 
   ObjectFile *object_file = m_objc_module_sp->GetObjectFile();
   if (!object_file)
     return;
 
   if (!object_file->IsInMemory())
     return;
 
   Target &target = GetProcess()->GetTarget();
   Debugger &debugger = target.GetDebugger();
-  if (auto stream = debugger.GetAsyncOutputStream()) {
-    const char *msg = "read from the shared cache";
-    if (PlatformSP platform_sp = target.GetPlatform())
-      msg = platform_sp->IsHost()
-                ? "read from the host's in-memory shared cache"
-                : "find the on-disk shared cache for this device";
-    stream->Printf("warning: libobjc.A.dylib is being read from process "
-                   "memory. This indicates that LLDB could not %s. This will "
-                   "likely reduce debugging performance.\n",
-                   msg);
+
+  std::string buffer;
+  llvm::raw_string_ostream os(buffer);
+
+  os << "warning: libobjc.A.dylib is being read from process memory. This "
+        "indicates that LLDB could not ";
+  if (PlatformSP platform_sp = target.GetPlatform()) {
+    if (platform_sp->IsHost()) {
+      os << "read from the host's in-memory shared cache";
+    } else {
+      os << "find the on-disk shared cache for this device";
+    }
+  } else {
+    os << "read from the shared cache";
   }
+  os << ". This will likely reduce debugging performance.\n";
+
+  Debugger::ReportWarning(os.str(), debugger.GetID(),
+                          &m_no_expanded_cache_warning);
 }
 
 DeclVendor *AppleObjCRuntimeV2::GetDeclVendor() {
   if (!m_decl_vendor_up)
     m_decl_vendor_up = std::make_unique<AppleObjCDeclVendor>(*this);
 
   return m_decl_vendor_up.get();
 }

lldb/unittests/Core/CMakeLists.txt

 add_lldb_unittest(LLDBCoreTests
   CommunicationTest.cpp
+  DiagnosticEventTest.cpp
   DumpDataExtractorTest.cpp
   FormatEntityTest.cpp
   MangledTest.cpp
   ModuleSpecTest.cpp
   RichManglingContextTest.cpp
   SourceLocationSpecTest.cpp
   SourceManagerTest.cpp
   StreamCallbackTest.cpp
   UniqueCStringMapTest.cpp
 
   LINK_LIBS
     lldbCore
     lldbHost
-    lldbSymbol
     lldbPluginObjectFileELF
     lldbPluginObjectFileMachO
     lldbPluginObjectFilePECOFF
+    lldbPluginPlatformMacOSX
     lldbPluginSymbolFileSymtab
+    lldbSymbol
     lldbUtilityHelpers
     LLVMTestingSupport
   LINK_COMPONENTS
     Support
   )

lldb/unittests/Core/DiagnosticEventTest.cpp

+//===-- DiagnosticEventTest.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 "gtest/gtest.h"
+
+#include "Plugins/Platform/MacOSX/PlatformMacOSX.h"
+#include "Plugins/Platform/MacOSX/PlatformRemoteMacOSX.h"
+#include "TestingSupport/SubsystemRAII.h"
+#include "lldb/Core/Debugger.h"
+#include "lldb/Core/DebuggerEvents.h"
+#include "lldb/Host/FileSystem.h"
+#include "lldb/Host/HostInfo.h"
+#include "lldb/Utility/Broadcaster.h"
+#include "lldb/Utility/Event.h"
+#include "lldb/Utility/Listener.h"
+#include "lldb/Utility/Reproducer.h"
+
+using namespace lldb;
+using namespace lldb_private;
+using namespace lldb_private::repro;
+
+static const constexpr std::chrono::seconds TIMEOUT(0);
+static const constexpr size_t DEBUGGERS = 3;
+
+static std::once_flag debugger_initialize_flag;
+
+namespace {
+class DiagnosticEventTest : public ::testing::Test {
+public:
+  void SetUp() override {
+    llvm::cantFail(Reproducer::Initialize(ReproducerMode::Off, llvm::None));
+    FileSystem::Initialize();
+    HostInfo::Initialize();
+    PlatformMacOSX::Initialize();
+    std::call_once(debugger_initialize_flag,
+                   []() { Debugger::Initialize(nullptr); });
+  }
+  void TearDown() override {
+    PlatformMacOSX::Terminate();
+    HostInfo::Terminate();
+    FileSystem::Terminate();
+    Reproducer::Terminate();
+  }
+};
+} // namespace
+
+TEST_F(DiagnosticEventTest, Warning) {
+  ArchSpec arch("x86_64-apple-macosx-");
+  Platform::SetHostPlatform(PlatformRemoteMacOSX::CreateInstance(true, &arch));
+
+  DebuggerSP debugger_sp = Debugger::CreateInstance();
+
+  Broadcaster &broadcaster = debugger_sp->GetBroadcaster();
+  ListenerSP listener_sp = Listener::MakeListener("test-listener");
+
+  listener_sp->StartListeningForEvents(&broadcaster,
+                                       Debugger::eBroadcastBitWarning);
+  EXPECT_TRUE(
+      broadcaster.EventTypeHasListeners(Debugger::eBroadcastBitWarning));
+
+  Debugger::ReportWarning("foo", debugger_sp->GetID());
+
+  EventSP event_sp;
+  EXPECT_TRUE(listener_sp->GetEvent(event_sp, TIMEOUT));
+  ASSERT_TRUE(event_sp);
+
+  const DiagnosticEventData *data =
+      DiagnosticEventData::GetEventDataFromEvent(event_sp.get());
+  ASSERT_NE(data, nullptr);
+  EXPECT_EQ(data->GetPrefix(), "warning");
+  EXPECT_EQ(data->GetMessage(), "foo");
+
+  Debugger::Destroy(debugger_sp);
+}
+
+TEST_F(DiagnosticEventTest, Error) {
+  ArchSpec arch("x86_64-apple-macosx-");
+  Platform::SetHostPlatform(PlatformRemoteMacOSX::CreateInstance(true, &arch));
+
+  DebuggerSP debugger_sp = Debugger::CreateInstance();
+
+  Broadcaster &broadcaster = debugger_sp->GetBroadcaster();
+  ListenerSP listener_sp = Listener::MakeListener("test-listener");
+
+  listener_sp->StartListeningForEvents(&broadcaster,
+                                       Debugger::eBroadcastBitError);
+  EXPECT_TRUE(broadcaster.EventTypeHasListeners(Debugger::eBroadcastBitError));
+
+  Debugger::ReportError("bar", debugger_sp->GetID());
+
+  EventSP event_sp;
+  EXPECT_TRUE(listener_sp->GetEvent(event_sp, TIMEOUT));
+  ASSERT_TRUE(event_sp);
+
+  const DiagnosticEventData *data =
+      DiagnosticEventData::GetEventDataFromEvent(event_sp.get());
+  ASSERT_NE(data, nullptr);
+  EXPECT_EQ(data->GetPrefix(), "error");
+  EXPECT_EQ(data->GetMessage(), "bar");
+
+  Debugger::Destroy(debugger_sp);
+}
+
+TEST_F(DiagnosticEventTest, MultipleDebuggers) {
+  ArchSpec arch("x86_64-apple-macosx-");
+  Platform::SetHostPlatform(PlatformRemoteMacOSX::CreateInstance(true, &arch));
+
+  std::vector<DebuggerSP> debuggers;
+  std::vector<ListenerSP> listeners;
+
+  for (size_t i = 0; i < DEBUGGERS; ++i) {
+    DebuggerSP debugger = Debugger::CreateInstance();
+    ListenerSP listener = Listener::MakeListener("listener");
+
+    debuggers.push_back(debugger);
+    listeners.push_back(listener);
+
+    listener->StartListeningForEvents(&debugger->GetBroadcaster(),
+                                      Debugger::eBroadcastBitError);
+  }
+
+  Debugger::ReportError("baz");
+
+  for (size_t i = 0; i < DEBUGGERS; ++i) {
+    EventSP event_sp;
+    EXPECT_TRUE(listeners[i]->GetEvent(event_sp, TIMEOUT));
+    ASSERT_TRUE(event_sp);
+
+    const DiagnosticEventData *data =
+        DiagnosticEventData::GetEventDataFromEvent(event_sp.get());
+    ASSERT_NE(data, nullptr);
+    EXPECT_EQ(data->GetPrefix(), "error");
+    EXPECT_EQ(data->GetMessage(), "baz");
+  }
+
+  for (size_t i = 0; i < DEBUGGERS; ++i) {
+    Debugger::Destroy(debuggers[i]);
+  }
+}
+
+TEST_F(DiagnosticEventTest, WarningOnce) {
+  ArchSpec arch("x86_64-apple-macosx-");
+  Platform::SetHostPlatform(PlatformRemoteMacOSX::CreateInstance(true, &arch));
+
+  DebuggerSP debugger_sp = Debugger::CreateInstance();
+
+  Broadcaster &broadcaster = debugger_sp->GetBroadcaster();
+  ListenerSP listener_sp = Listener::MakeListener("test-listener");
+
+  listener_sp->StartListeningForEvents(&broadcaster,
+                                       Debugger::eBroadcastBitWarning);
+  EXPECT_TRUE(
+      broadcaster.EventTypeHasListeners(Debugger::eBroadcastBitWarning));
+
+  std::once_flag once;
+  Debugger::ReportWarning("foo", debugger_sp->GetID(), &once);
+
+  {
+    EventSP event_sp;
+    EXPECT_TRUE(listener_sp->GetEvent(event_sp, TIMEOUT));
+    ASSERT_TRUE(event_sp);
+
+    const DiagnosticEventData *data =
+        DiagnosticEventData::GetEventDataFromEvent(event_sp.get());
+    ASSERT_NE(data, nullptr);
+    EXPECT_EQ(data->GetPrefix(), "warning");
+    EXPECT_EQ(data->GetMessage(), "foo");
+  }
+
+  EventSP second_event_sp;
+  EXPECT_FALSE(listener_sp->GetEvent(second_event_sp, TIMEOUT));
+
+  Debugger::ReportWarning("foo", debugger_sp->GetID(), &once);
+  EXPECT_FALSE(listener_sp->GetEvent(second_event_sp, TIMEOUT));
+
+  Debugger::ReportWarning("foo", debugger_sp->GetID());
+  EXPECT_TRUE(listener_sp->GetEvent(second_event_sp, TIMEOUT));
+
+  Debugger::Destroy(debugger_sp);
+}