[cxxmodules] Only load modules if one was generated

If we generate a dictionary with a C++ module with rootcling we
should write in the payload that we generated a C++ module.
This way we can actually print a *reliable* warning when we fail
to load the C++ module during runtime. Without this we can only
speculate if a missing C++ module is intentional.

core/base/inc/TROOT.h

@@ -309,7 +309,8 @@ friend TROOT *ROOT::Internal::GetROOT2();
                                     const char* fwdDeclCode,
                                     void (*triggerFunc)(),
                                     const FwdDeclArgsToKeepCollection_t& fwdDeclsArgToSkip,
-                                    const char** classesHeaders);
+                                    const char** classesHeaders,
+                                    bool hasCxxModule = false);
    TObject          *Remove(TObject*);
    void              RemoveClass(TClass *);
    void              Reset(Option_t *option="");

core/base/src/TROOT.cxx

@@ -258,15 +258,17 @@ namespace {
                          const char* fwdDeclCode,
                          void (*triggerFunc)(),
                          const TROOT::FwdDeclArgsToKeepCollection_t& fwdDeclsArgToSkip,
-                         const char** classesHeaders):
+                         const char **classesHeaders,
+                         bool hasCxxModule):
                            fModuleName(moduleName),
                            fHeaders(headers),
                            fPayloadCode(payloadCode),
                            fFwdDeclCode(fwdDeclCode),
                            fIncludePaths(includePaths),
                            fTriggerFunc(triggerFunc),
                            fClassesHeaders(classesHeaders),
-                           fFwdNargsToKeepColl(fwdDeclsArgToSkip){}
+                           fFwdNargsToKeepColl(fwdDeclsArgToSkip),
+                           fHasCxxModule(hasCxxModule) {}
 
       const char* fModuleName; // module name
       const char** fHeaders; // 0-terminated array of header files
@@ -277,6 +279,7 @@ namespace {
       const char** fClassesHeaders; // 0-terminated list of classes and related header files
       const TROOT::FwdDeclArgsToKeepCollection_t fFwdNargsToKeepColl; // Collection of
                                                                       // pairs of template fwd decls and number of
+      bool fHasCxxModule; // Whether this module has a C++ module alongside it.
    };
 
    std::vector<ModuleHeaderInfo_t>& GetModuleHeaderInfoBuffer() {
@@ -2068,7 +2071,8 @@ void TROOT::InitInterpreter()
                                    li->fTriggerFunc,
                                    li->fFwdNargsToKeepColl,
                                    li->fClassesHeaders,
-                                   kTRUE /*lateRegistration*/);
+                                   kTRUE /*lateRegistration*/,
+                                   li->fHasCxxModule);
    }
    GetModuleHeaderInfoBuffer().clear();
 
@@ -2477,7 +2481,8 @@ void TROOT::RegisterModule(const char* modulename,
                            const char* fwdDeclCode,
                            void (*triggerFunc)(),
                            const TInterpreter::FwdDeclArgsToKeepCollection_t& fwdDeclsArgToSkip,
-                           const char** classesHeaders)
+                           const char** classesHeaders,
+                           bool hasCxxModule)
 {
 
    // First a side track to insure proper end of process behavior.
@@ -2539,12 +2544,12 @@ void TROOT::RegisterModule(const char* modulename,
 
    // Now register with TCling.
    if (gCling) {
-      gCling->RegisterModule(modulename, headers, includePaths, payloadCode, fwdDeclCode,
-                             triggerFunc, fwdDeclsArgToSkip, classesHeaders);
+      gCling->RegisterModule(modulename, headers, includePaths, payloadCode, fwdDeclCode, triggerFunc,
+                             fwdDeclsArgToSkip, classesHeaders, false, hasCxxModule);
    } else {
-      GetModuleHeaderInfoBuffer()
-         .push_back(ModuleHeaderInfo_t (modulename, headers, includePaths, payloadCode, fwdDeclCode,
-                                        triggerFunc, fwdDeclsArgToSkip,classesHeaders));
+      GetModuleHeaderInfoBuffer().push_back(ModuleHeaderInfo_t(modulename, headers, includePaths, payloadCode,
+                                                               fwdDeclCode, triggerFunc, fwdDeclsArgToSkip,
+                                                               classesHeaders, hasCxxModule));
    }
 }
 

core/dictgen/src/TModuleGenerator.cxx

@@ -462,7 +462,7 @@ void TModuleGenerator::WriteRegistrationSource(std::ostream &out,
                               "    if (!isInitialized) {\n"
                               "      TROOT::RegisterModule(\"" << GetDemangledDictionaryName() << "\",\n"
                               "        headers, includePaths, payloadCode, fwdDeclCode,\n"
-                              "        TriggerDictionaryInitialization_" << GetDictionaryName() << "_Impl, " << fwdDeclnArgsToKeepString << ", classesHeaders);\n"
+                              "        TriggerDictionaryInitialization_" << GetDictionaryName() << "_Impl, " << fwdDeclnArgsToKeepString << ", classesHeaders, " << (fCI->getLangOpts().Modules ? "/*has C++ module*/true" : "/*has no C++ module*/false") << ");\n"
                               "      isInitialized = true;\n"
                               "    }\n"
                               "  }\n"

core/meta/inc/TInterpreter.h

@@ -154,7 +154,8 @@ class TInterpreter : public TNamed {
                                    void (* /*triggerFunc*/)(),
                                    const FwdDeclArgsToKeepCollection_t& fwdDeclArgsToKeep,
                                    const char** classesHeaders,
-                                   Bool_t lateRegistration = false) = 0;
+                                   Bool_t lateRegistration = false,
+                                   Bool_t hasCxxModule = false) = 0;
    virtual void     RegisterTClassUpdate(TClass *oldcl,DictFuncPtr_t dict) = 0;
    virtual void     UnRegisterTClassUpdate(const TClass *oldcl) = 0;
    virtual Int_t    SetClassSharedLibs(const char *cls, const char *libs) = 0;

core/metacling/src/TCling.cxx

@@ -1673,7 +1673,8 @@ void TCling::RegisterModule(const char* modulename,
                             void (*triggerFunc)(),
                             const FwdDeclArgsToKeepCollection_t& fwdDeclsArgToSkip,
                             const char** classesHeaders,
-                            Bool_t lateRegistration /*=false*/)
+                            Bool_t lateRegistration /*=false*/,
+                            Bool_t hasCxxModule /*=false*/)
 {
    const bool fromRootCling = IsFromRootCling();
    // We need the dictionary initialization but we don't want to inject the
@@ -1913,7 +1914,7 @@ void TCling::RegisterModule(const char* modulename,
    clang::Sema &TheSema = fInterpreter->getSema();
 
    bool ModuleWasSuccessfullyLoaded = false;
-   if (TheSema.getLangOpts().Modules) {
+   if (hasCxxModule) {
       std::string ModuleName = llvm::StringRef(modulename).substr(3).str();
       ModuleWasSuccessfullyLoaded = LoadModule(ModuleName, *fInterpreter);
       if (!ModuleWasSuccessfullyLoaded) {

core/metacling/src/TCling.h

@@ -205,7 +205,8 @@ class TCling : public TInterpreter {
                           void (*triggerFunc)(),
                           const FwdDeclArgsToKeepCollection_t& fwdDeclsArgToSkip,
                           const char** classesHeaders,
-                          Bool_t lateRegistration = false);
+                          Bool_t lateRegistration = false,
+                          Bool_t hasCxxModule = false);
    void    RegisterTClassUpdate(TClass *oldcl,DictFuncPtr_t dict);
    void    UnRegisterTClassUpdate(const TClass *oldcl);