Use MessageSvc to handle ROOT messages

The default ROOT error handler (the equivalent of Gaudi MessageSvc) prints messages to stderr, which is problematic with Gaudi based workflows that expect all messages to go through stdout and be filtered according to MessageSvc output level.

This MR replaces the ROOT error handler with an adapter function that redirects to MessageSvc.

There are a couple of drawbacks which the changes proposed here:

• it works only if ROOT (gROOT) has been initialized before ApplicationMgr::configure, but my tests suggest this is always the case
• every message sent by ROOT makes a call to IMessageSvc::outputLevel( source ) to decide if the message has to be printed or not, while MsgStream instances cache the thresholds; we can optimize the adapter caching internally the thresholds (e.g. with a static std::unordered_map<std::string, int> thresholds) or by using a global threshold for ROOT messages.

GaudiCoreSvc/src/ApplicationMgr/ApplicationMgr.cpp

 /***********************************************************************************\
-* (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
+* (c) Copyright 1998-2023 CERN for the benefit of the LHCb and ATLAS collaborations *
 *                                                                                   *
 * This software is distributed under the terms of the Apache version 2 licence,     *
 * copied verbatim in the file "LICENSE".                                            *
@@ -9,44 +9,73 @@
 * or submit itself to any jurisdiction.                                             *
 \***********************************************************************************/
 
-// Include files
 #include "ApplicationMgr.h"
-
 #include "AlgorithmManager.h"
 #include "DLLClassManager.h"
 #include "ServiceManager.h"
-
-#include "GaudiKernel/IMessageSvc.h"
-#include "GaudiKernel/IRunable.h"
-#include "GaudiKernel/IService.h"
-#include "GaudiKernel/TypeNameString.h"
-
-#include "GaudiKernel/MsgStream.h"
-#include "GaudiKernel/ObjectFactory.h"
-#include "GaudiKernel/SmartIF.h"
-
-#include "GaudiKernel/GaudiException.h"
-
-#include "GaudiKernel/StatusCode.h"
-#include "GaudiKernel/System.h"
-#include "GaudiKernel/Time.h"
-
-#include "GAUDI_VERSION.h"
-
-using System::getEnv;
-using System::isEnvSet;
-
+#include <GAUDI_VERSION.h>
+#include <GaudiKernel/GaudiException.h>
+#include <GaudiKernel/IMessageSvc.h>
+#include <GaudiKernel/IRunable.h>
+#include <GaudiKernel/IService.h>
+#include <GaudiKernel/Message.h>
+#include <GaudiKernel/MsgStream.h>
+#include <GaudiKernel/ObjectFactory.h>
+#include <GaudiKernel/SmartIF.h>
+#include <GaudiKernel/StatusCode.h>
+#include <GaudiKernel/System.h>
+#include <GaudiKernel/Time.h>
+#include <GaudiKernel/TypeNameString.h>
+#include <TError.h>
+#include <TROOT.h>
 #include <algorithm>
 #include <cassert>
 #include <ctime>
 #include <limits>
 #include <sstream>
 
+using System::getEnv;
+using System::isEnvSet;
+
 #define ON_DEBUG if ( m_outputLevel <= MSG::DEBUG )
 #define ON_VERBOSE if ( m_outputLevel <= MSG::VERBOSE )
 
 DECLARE_OBJECT_FACTORY( ApplicationMgr )
 
+namespace {
+  /// Pointer to the IMessageSvc instance used by ROOTErrorHandlerAdapter.
+  static IMessageSvc* s_messageSvcInstance{ nullptr };
+  /// Pointer to the ROOT error handler registered before we replaced it with ROOTErrorHandlerAdapter.
+  static ErrorHandlerFunc_t s_originalRootErrorHandler{ nullptr };
+
+  /// @brief Adapter to forward ROOT messages to a MessageSvc.
+  void ROOTErrorHandlerAdapter( int level, Bool_t abort, const char* location, const char* msg ) {
+    if ( s_messageSvcInstance ) {
+      // we pass the message to MessageSvc only if it is not suppressed by ROOT itself
+      if ( level >= gErrorIgnoreLevel ) {
+        // # Map ROOT level to Gaudi level:
+        // ROOT levels go from 0 to 6000 in step of 1000,
+        // kInfo is 1000 while MSG::INFO is 3, so we aim for `level / 1000 + 2`,
+        // but we have to put a cap at MSG::FATAL.
+        int msgLevel = std::min<int>( level / 1000 + 2, MSG::FATAL );
+        if ( msgLevel >= s_messageSvcInstance->outputLevel( location ) ) {
+          s_messageSvcInstance->reportMessage( Message{ location, msgLevel, msg }, msgLevel );
+        }
+      }
+    } else {
+      // If a message is sent when we do not have an IMessageSvc, let's use something else
+      if ( s_originalRootErrorHandler ) {
+        // either the original handler (if any)
+        s_originalRootErrorHandler( level, abort, location, msg );
+      } else {
+        // or some minimalistic implementation from ROOT (just not to loose the message)
+        ROOT::Internal::MinimalErrorHandler( level, abort, location, msg );
+      }
+    }
+  }
+
+} // namespace
+
 // Implementation class for the Application Manager. In this way the
 // ApplicationMgr class is a fully insulated concrete class. Clients
 // (main programs) will not need to re-compile if there are changes
@@ -145,6 +174,18 @@ StatusCode ApplicationMgr::i_startup() {
     log << MSG::FATAL << "Error setting OutputLevel option of MessageSvc" << endmsg;
     return sc;
   }
+  if ( m_useMessageSvcForROOTMessages ) {
+    if ( gROOT ) {
+      // if ROOT is already initialized (usually it is the case) we redirect messages to MessageSvc.
+      s_messageSvcInstance       = m_messageSvc.get();
+      s_originalRootErrorHandler = SetErrorHandler( ROOTErrorHandlerAdapter );
+    } else {
+      log << MSG::WARNING
+          << "ROOT not yet initialized, we cannot override the error handler are requested "
+             "(UseMessageSvcForROOTMessages==true)"
+          << endmsg;
+    }
+  }
 
   auto jobsvc = svcManager()->createService( Gaudi::Utils::TypeNameString( "JobOptionsSvc", m_jobOptionsSvcType ) );
   // Create the Job Options service
@@ -620,6 +661,13 @@ StatusCode ApplicationMgr::terminate() {
     opts.set( "JobOptionsSvc.AuditFinalize", "false" );
   }
 
+  // if we have overriden it, restore the original ROOT error handler
+  if ( s_originalRootErrorHandler ) {
+    SetErrorHandler( s_originalRootErrorHandler );
+    s_originalRootErrorHandler = nullptr;
+  }
+  // make sure ROOTErrorHandlerAdapter (if in use) does not try to use the MessageSvc we are about to delete
+  s_messageSvcInstance = nullptr;
   // finalize MessageSvc
   auto svc = m_messageSvc.as<IService>();
   if ( !svc ) {