[io] in TDirectoryFile::mkdir, only apply title to the innermost dir.

Author: silverweed

io/io/src/TDirectoryFile.cxx

@@ -1258,7 +1258,9 @@ TFile *TDirectoryFile::OpenFile(const char *name, Option_t *option,const char *f
 /// Create a sub-directory "a" or a hierarchy of sub-directories "a/b/c/...".
 ///
 /// @param name the name or hierarchy of the subdirectory ("a" or "a/b/c")
-/// @param title the title
+/// @param title the title of the directory. For hierarchies, this is only applied
+/// to the innermost directory (so if `name == "a/b/c"` and `title == "my dir"`,
+/// only `c` will have the title `"my dir"`).
 /// @param returnExistingDirectory if key-name is already existing, the returned
 /// value points to preexisting sub-directory if true and to `nullptr` if false.
 /// @return a pointer to the created sub-directory, not to the top sub-directory
@@ -1284,10 +1286,11 @@ TDirectory *TDirectoryFile::mkdir(const char *name, const char *title, Bool_t re
       TDirectoryFile *tmpdir = nullptr;
       GetObject(workname.Data(), tmpdir);
       if (!tmpdir) {
-         tmpdir = (TDirectoryFile*)mkdir(workname.Data(),title);
+         // We give all intermediate directories a default title, as `title` is only given to the innermost dir.
+         tmpdir = (TDirectoryFile *)mkdir(workname.Data(), workname.Data());
          if (!tmpdir) return nullptr;
       }
-      return tmpdir->mkdir(slash + 1, "", returnExistingDirectory);
+      return tmpdir->mkdir(slash + 1, title, returnExistingDirectory);
    }
 
    TDirectory::TContext ctxt(this);

io/io/test/TFileTests.cxx

@@ -285,16 +285,23 @@ TEST(TDirectoryFile, SeekParent)
 TEST(TDirectoryFile, RecursiveMkdir)
 {
    TMemFile f("mkdirtest.root", "RECREATE");
-   auto dir1 = f.mkdir("a/b/c");
+   auto dir1 = f.mkdir("a/b/c", "my dir");
    EXPECT_NE(dir1, nullptr);
    {
       ROOT::TestSupport::CheckDiagsRAII diags;
       diags.requiredDiag(kError, "TDirectoryFile::mkdir","An object with name c exists already");
       auto dir2 = f.mkdir("a/b/c", "", /* returnExisting = */ false);
       EXPECT_EQ(dir2, nullptr);
    }
-   auto dir3 = f.mkdir("a/b/c", "", /* returnExisting = */ true);
+   auto dir3 = f.mkdir("a/b/c", "foobar", /* returnExisting = */ true);
    EXPECT_EQ(dir3, dir1);
+   EXPECT_STREQ(dir3->GetTitle(), "my dir");
+   auto dirB = dir3->GetMotherDir();
+   ASSERT_NE(dirB, nullptr);
+   EXPECT_STREQ(dirB->GetTitle(), "b");
+   auto dirA = dirB->GetMotherDir();
+   ASSERT_NE(dirA, nullptr);
+   EXPECT_STREQ(dirA->GetTitle(), "a");
 }
 
 // https://its.cern.ch/jira/browse/ROOT-10581