[cxxmodules] Do not generate rdict files if we have a module.

The rdict file does not show performance benefits anymore and
we are as good as having only a C++ module.

Author: vgvassilev

cmake/modules/RootNewMacros.cmake

@@ -389,6 +389,7 @@ function(ROOT_GENERATE_DICTIONARY dictionary)
 
   if(cpp_module_file)
     set(newargs -cxxmodule ${newargs})
+    set(pcm_name)
   endif()
 
   #---what rootcling command to use--------------------------

core/dictgen/src/rootcling_impl.cxx

@@ -2984,8 +2984,8 @@ int CheckClassesForInterpreterOnlyDicts(cling::Interpreter &interp,
 ////////////////////////////////////////////////////////////////////////////////
 /// Make up for skipping RegisterModule, now that dictionary parsing
 /// is done and these headers cannot be selected anymore.
-
-int FinalizeStreamerInfoWriting(cling::Interpreter &interp, bool writeEmptyRootPCM=false)
+///
+int MaybeEmitROOTPCM(cling::Interpreter &interp, bool writeEmptyRootPCM=false)
 {
    if (!gDriverConfig->fCloseStreamerInfoROOTFile)
       return 0;
@@ -3022,7 +3022,8 @@ int GenerateFullDict(std::ostream &dictStream,
                      const ROOT::TMetaUtils::RConstructorTypes &ctorTypes,
                      bool isSplit,
                      bool isGenreflex,
-                     bool writeEmptyRootPCM)
+                     bool writeEmptyRootPCM,
+                     bool hasCxxModule)
 {
    ROOT::TMetaUtils::TNormalizedCtxt normCtxt(interp.getLookupHelper());
 
@@ -3134,12 +3135,12 @@ int GenerateFullDict(std::ostream &dictStream,
    // coverity[fun_call_w_exception] - that's just fine.
    ROOT::Internal::RStl::Instance().WriteClassInit(dictStream, interp, normCtxt, ctorTypes, needsCollectionProxy, EmitStreamerInfo);
 
-   if (!gDriverConfig->fBuildingROOTStage1) {
+   if (!hasCxxModule && !gDriverConfig->fBuildingROOTStage1) {
       EmitTypedefs(scan.fSelectedTypedefs);
       EmitEnums(scan.fSelectedEnums);
       // Make up for skipping RegisterModule, now that dictionary parsing
       // is done and these headers cannot be selected anymore.
-      int finRetCode = FinalizeStreamerInfoWriting(interp, writeEmptyRootPCM);
+      int finRetCode = MaybeEmitROOTPCM(interp, writeEmptyRootPCM);
       if (finRetCode != 0) return finRetCode;
    }
 
@@ -5013,17 +5014,18 @@ int RootClingMain(int argc,
       rootclingRetCode += CheckClassesForInterpreterOnlyDicts(interp, scan);
       // generate an empty pcm nevertheless for consistency
       // Negate as true is 1 and true is returned in case of success.
-      if (!gDriverConfig->fBuildingROOTStage1) {
-         rootclingRetCode +=  FinalizeStreamerInfoWriting(interp);
+      if (!cxxmodule && !gDriverConfig->fBuildingROOTStage1) {
+         rootclingRetCode += MaybeEmitROOTPCM(interp);
       }
    } else {
       rootclingRetCode += GenerateFullDict(splitDictStream,
-                                 interp,
-                                 scan,
-                                 constructorTypes,
-                                 doSplit,
-                                 isGenreflex,
-                                 writeEmptyRootPCM);
+                                           interp,
+                                           scan,
+                                           constructorTypes,
+                                           doSplit,
+                                           isGenreflex,
+                                           writeEmptyRootPCM,
+                                           cxxmodule);
    }
 
    if (rootclingRetCode != 0) {