[PyROOT] Don't assume ownership of TTree created by CloneTree()

Just like in the case of the TTree constructor, Python does not own the
TTree if the current directory is a TFile.

Fixes a failure in the CMSSW unit tests.

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_ttree.py

@@ -308,6 +308,20 @@ def _TTree__getattr__(self, key):
         out = cppyy.ll.cast[cast_type](out)
     return out
 
+def _TTree_CloneTree(self, *args, **kwargs):
+    """
+    Forward the arguments to the C++ function and give up ownership if the
+    TTree is attached to a TFile, which is the owner in that case.
+    """
+    import ROOT
+
+    out_tree = self._CloneTree(*args, **kwargs)
+    tdir = out_tree.GetDirectory()
+    if tdir and type(tdir).__cpp_name__ == "TFile":
+        ROOT.SetOwnership(out_tree, False)
+
+    return out_tree
+
 def _TTree_Constructor(self, *args, **kwargs):
     """
     Forward the arguments to the C++ constructor and give up ownership if the
@@ -326,9 +340,14 @@ def pythonize_ttree(klass, name):
     # klass: class to be pythonized
     # name: string containing the name of the class
 
+    # Functions that need to drop the ownership if the current directory is a TFile
+
     klass._cpp_constructor = klass.__init__
     klass.__init__ = _TTree_Constructor
 
+    klass._CloneTree = klass.CloneTree
+    klass.CloneTree = _TTree_CloneTree
+
     # Pythonizations that are common to TTree and its subclasses.
     # To avoid duplicating the same logic in the pythonizors of
     # the subclasses, inject the pythonizations for all the target

bindings/pyroot/pythonizations/test/memory.py

@@ -1,5 +1,6 @@
-import gc
 import ROOT
+import gc
+import os
 import unittest
 
 
@@ -71,5 +72,18 @@ def test_tcolor_memory_regulation(self):
         # application does not segfault
         c = ROOT.TColor(42, 42, 42)
 
+    def test_ttree_clone_in_file_context(self):
+        """Test that CloneTree() doesn't give the ownership to Python when
+        TFile is opened."""
+
+        filename = "test_ttree_clone_in_file_context"
+
+        ttree = ROOT.TTree("tree", "tree")
+
+        with ROOT.TFile(filename, "RECREATE") as infile:
+            ttree_clone = ttree.CloneTree()
+
+        os.remove(filename)
+
 if __name__ == '__main__':
     unittest.main()