[io] do not use single-file-merge shortcut if filters are specified

Fixes #13359

io/io/src/TFileMerger.cxx

@@ -483,7 +483,6 @@ Bool_t TFileMerger::MergeOne(TDirectory *target, TList *sourcelist, Int_t type,
    }
    // Check if only the listed objects are to be merged
    if (type & kOnlyListed) {
-      onlyListed = kFALSE;
       oldkeyname = keyname;
       oldkeyname += " ";
       onlyListed = fObjectNames.Contains(oldkeyname);
@@ -909,14 +908,18 @@ Bool_t TFileMerger::MergeRecursive(TDirectory *target, TList *sourcelist, Int_t
 /// the file "FileMerger.root" in the working directory. Returns true
 /// on success, false in case of error.
 /// The type is defined by the bit values in EPartialMergeType:
-///   kRegular      : normal merge, overwritting the output file
-///   kIncremental  : merge the input file with the content of the output file (if already exising) (default)
-///   kAll          : merge all type of objects (default)
-///   kResetable    : merge only the objects with a MergeAfterReset member function.
-///   kNonResetable : merge only the objects without a MergeAfterReset member function.
+///   kRegular        : normal merge, overwritting the output file
+///   kIncremental    : merge the input file with the content of the output file (if already exising) (default)
+///   kResetable      : merge only the objects with a MergeAfterReset member function.
+///   kNonResetable   : merge only the objects without a MergeAfterReset member function.
+///   kDelayWrite     : delay the TFile write (to reduce the number of write when reusing the file)
+///   kAll            : merge all type of objects (default)
+///   kAllIncremental : merge incrementally all type of objects.
+///   kOnlyListed     : merge only the objects specified in fObjectNames list
+///   kSkipListed     : skip objects specified in fObjectNames list
+///   kKeepCompression: keep compression level unchanged for each input
 ///
-/// If the type is set to kIncremental the output file is done deleted at the end of
-/// this operation.  If the type is not set to kIncremental, the output file is closed.
+/// If the type is not set to kIncremental, the output file is deleted at the end of this operation.
 
 Bool_t TFileMerger::PartialMerge(Int_t in_type)
 {
@@ -933,9 +936,9 @@ Bool_t TFileMerger::PartialMerge(Int_t in_type)
       }
    }
 
-   // Special treament for the single file case ...
+   // Special treament for the single file case to improve efficiency...
    if ((fFileList.GetEntries() == 1) && !fExcessFiles.GetEntries() &&
-      !(in_type & kIncremental) && !fCompressionChange && !fExplicitCompLevel) {
+      !(in_type & (kIncremental | kOnlyListed | kSkipListed | kResetable | kNonResetable)) && !fCompressionChange && !fExplicitCompLevel) {
       fOutputFile->Close();
       SafeDelete(fOutputFile);
 

io/io/test/CMakeLists.txt

@@ -9,7 +9,7 @@ ROOT_ADD_GTEST(TFile TFileTests.cxx LIBRARIES RIO)
 ROOT_ADD_GTEST(TBufferFile TBufferFileTests.cxx LIBRARIES RIO)
 ROOT_ADD_GTEST(TBufferMerger TBufferMerger.cxx LIBRARIES RIO Imt Tree)
 ROOT_ADD_GTEST(TBufferJSON TBufferJSONTests.cxx LIBRARIES RIO)
-ROOT_ADD_GTEST(TFileMerger TFileMergerTests.cxx LIBRARIES RIO Tree)
+ROOT_ADD_GTEST(TFileMerger TFileMergerTests.cxx LIBRARIES RIO Tree Hist)
 ROOT_ADD_GTEST(TROMemFile TROMemFileTests.cxx LIBRARIES RIO Tree)
 if(uring AND NOT DEFINED ENV{ROOTTEST_IGNORE_URING})
   ROOT_ADD_GTEST(RIoUring RIoUring.cxx LIBRARIES RIO)

io/io/test/TFileMergerTests.cxx

@@ -4,6 +4,7 @@
 
 #include "TMemFile.h"
 #include "TTree.h"
+#include "TH1.h"
 
 static void CreateATuple(TMemFile &file, const char *name, double value)
 {
@@ -51,7 +52,8 @@ TEST(TFileMerger, CreateWithTFilePointer)
    merger.AddFile(&a, false);
    merger.AddFile(&b, false);
    // FIXME: Calling merger.Merge() will call Close() and *delete* output.
-   merger.PartialMerge();
+   success = merger.PartialMerge();
+   ASSERT_TRUE(success);
 
    auto &result = *static_cast<TMemFile *>(merger.GetOutputFile());
    CheckTree(result, "a_tree", 1);
@@ -68,3 +70,34 @@ TEST(TFileMerger, CreateWithUnwritableTFilePointer)
    ROOT_EXPECT_ERROR(merger.OutputFile(std::move(output)), "TFileMerger::OutputFile",
                      "output file output.root is not writable");
 }
+
+TEST(TFileMerger, MergeSingleOnlyListed)
+{
+   TMemFile a("hist4.root", "CREATE");
+
+   auto hist1 = new TH1F("hist1", "hist1", 1 , 0 , 2);
+   auto hist2 = new TH1F("hist2", "hist2", 1 , 0 , 2);
+   auto hist3 = new TH1F("hist3", "hist3", 1 , 0 , 2);
+   auto hist4 = new TH1F("hist4", "hist4", 1 , 0 , 2);
+   hist1->Fill(1);
+   hist2->Fill(1);   hist2->Fill(2);
+   hist3->Fill(1);   hist3->Fill(1);   hist3->Fill(1);
+   hist4->Fill(1);   hist4->Fill(1);   hist4->Fill(1);   hist4->Fill(1);
+   a.Write();
+
+   TFileMerger merger;
+   auto output = std::unique_ptr<TFile>(new TFile("SingleOnlyListed.root", "RECREATE"));
+   bool success = merger.OutputFile(std::move(output));
+   ASSERT_TRUE(success);
+
+   merger.AddObjectNames("hist1");
+   merger.AddObjectNames("hist2");
+   merger.AddFile(&a, false);
+   const Int_t mode = (TFileMerger::kAll | TFileMerger::kRegular | TFileMerger::kOnlyListed);
+   success = merger.PartialMerge(mode); // This will delete fOutputFile as we are not using kIncremental, so merger.GetOutputFile() will return a nullptr
+   ASSERT_TRUE(success);
+
+   output = std::unique_ptr<TFile>(TFile::Open("SingleOnlyListed.root"));
+   ASSERT_TRUE(output.get() && output->GetListOfKeys());
+   EXPECT_EQ(output->GetListOfKeys()->GetSize(), 2);
+}