[RF] Consider the SplitRange in overlap checks for simultaneous PDFs

When the `SplitRange` command arguemnt is used in
`RooAbsPdf::createNLL`, the actual range names used for the fit depend
on the channel, with the range names suffixed by the category name. This
should be considered correctly in the overlap checks.

Closes root-project#11396.

roofit/roofitcore/inc/RooHelpers.h

@@ -132,7 +132,10 @@ class ChangeOperModeRAII {
 
 std::pair<double, double> getRangeOrBinningInterval(RooAbsArg const* arg, const char* rangeName);
 
-bool checkIfRangesOverlap(RooAbsPdf const& pdf, RooAbsData const& data, std::vector<std::string> const& rangeNames);
+bool checkIfRangesOverlap(RooAbsPdf const& pdf,
+                          RooAbsData const& data,
+                          std::vector<std::string> const& rangeNames,
+                          bool splitRange);
 
 std::string getColonSeparatedNameString(RooArgSet const& argSet);
 RooArgSet selectFromArgSet(RooArgSet const&, std::string const& names);

roofit/roofitcore/src/RooAbsPdf.cxx

@@ -1143,7 +1143,7 @@ RooAbsReal* RooAbsPdf::createNLL(RooAbsData& data, const RooLinkedList& cmdList)
     // Composite case: multiple ranges
     RooArgList nllList ;
     auto tokens = ROOT::Split(rangeName, ",");
-    if (RooHelpers::checkIfRangesOverlap(*this, data, tokens)) {
+    if (RooHelpers::checkIfRangesOverlap(*this, data, tokens, cfg.splitCutRange)) {
       throw std::runtime_error(
               std::string("Error in RooAbsPdf::createNLL! The ranges ") + rangeName + " are overlapping!");
     }

roofit/roofitcore/src/RooHelpers.cxx

@@ -14,17 +14,19 @@
  * listed in LICENSE (http://roofit.sourceforge.net/license.txt)             *
  *****************************************************************************/
 
-#include "RooHelpers.h"
-#include "RooAbsPdf.h"
-#include "RooAbsData.h"
-#include "RooDataHist.h"
-#include "RooDataSet.h"
-#include "RooAbsRealLValue.h"
-#include "RooArgList.h"
-#include "RooAbsCategory.h"
-
-#include "ROOT/StringUtils.hxx"
-#include "TClass.h"
+#include <RooHelpers.h>
+
+#include <RooAbsCategory.h>
+#include <RooAbsData.h>
+#include <RooAbsPdf.h>
+#include <RooAbsRealLValue.h>
+#include <RooArgList.h>
+#include <RooDataHist.h>
+#include <RooDataSet.h>
+#include <RooSimultaneous.h>
+
+#include <ROOT/StringUtils.hxx>
+#include <TClass.h>
 
 namespace RooHelpers {
 
@@ -182,7 +184,35 @@ std::pair<double, double> getRangeOrBinningInterval(RooAbsArg const* arg, const
 /// \param[in] pdf the PDF
 /// \param[in] data RooAbsCollection with the observables to check for overlap.
 /// \param[in] rangeNames The names of the ranges.
-bool checkIfRangesOverlap(RooAbsPdf const& pdf, RooAbsData const& data, std::vector<std::string> const& rangeNames) {
+/// \param[in] splitRange If `true`, each component of a RooSimultaneous will
+///                       be checked individually for overlaps, with the range
+///                       names in that component suffixed by `_<cat_label>`.
+///                       See the `SplitRange()` command argument of
+///                       RooAbsPdf::fitTo()` to understand where this is used.
+bool checkIfRangesOverlap(RooAbsPdf const& pdf,
+                          RooAbsData const& data,
+                          std::vector<std::string> const& rangeNames,
+                          bool splitRange)
+{
+  // If the PDF is a RooSimultaneous and the `splitRange` option is set, we
+  // have to check each component PDF with a different set of rangeNames, each
+  // suffixed by the category name.
+  if(splitRange && dynamic_cast<RooSimultaneous const*>(&pdf)) {
+    auto const& simPdf = static_cast<RooSimultaneous const&>(pdf);
+    bool hasOverlap = false;
+    std::vector<std::string> rangeNamesSplit;
+    for (const auto& catState : simPdf.indexCat()) {
+      const std::string& catName = catState.first;
+      for(std::string const& rangeName : rangeNames) {
+        rangeNamesSplit.emplace_back(rangeName + "_" + catName);
+      }
+      hasOverlap |= checkIfRangesOverlap(*simPdf.getPdf(catName.c_str()), data, rangeNamesSplit, false);
+
+      rangeNamesSplit.clear();
+    }
+
+    return hasOverlap;
+  }
 
   auto observables = *pdf.getObservables(data);