fix: models should not be wrapped in a ListOffsetForm (#841)

* fix:models should not be wrapped in a ListOffsetForm

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Changed test file name to match PR nr.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/uproot/containers.py

@@ -328,14 +328,11 @@ def typename(self):
             return uproot.model.classname_decode(self._model.__name__)[0]
 
     def awkward_form(self, file, context):
-        awkward = uproot.extras.awkward()
+        uproot.extras.awkward()
         if self._model is None:
             raise uproot.interpretation.objects.CannotBeAwkward("dynamic type")
         else:
-            return awkward.forms.ListOffsetForm(
-                context["index_format"],
-                uproot._util.awkward_form(self._model, file, context),
-            )
+            return uproot._util.awkward_form(self._model, file, context)
 
     def read(self, chunk, cursor, context, file, selffile, parent, header=True):
         # AwkwardForth testing: test_0637's tests aren't expected to enter here

tests/test_0841-fix-814.p

@@ -0,0 +1,29 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/uproot4/blob/main/LICENSE
+import os
+import numpy
+import pytest
+import uproot
+
+pytest.importorskip("ROOT")
+
+
+def test_1(tmp_path):
+    filename = os.path.join(tmp_path, "tfile_with_tvector3_1.root")
+    tfile = ROOT.TFile(filename, "RECREATE")
+    tree = ROOT.TTree("tree", "tree")
+    tvector3 = ROOT.TVector3()
+    tree.Branch("tvector3", tvector3)
+    for x in range(10):
+        tvector3.SetX(x)
+        tree.Fill()
+    tree.AutoSave()
+    tfile.Close()
+    uproot.open("tfile_with_tvector3_1.root:tree").arrays()
+
+    tfile = ROOT.TFile(filename, "READ")
+    tree = tfile.Get("tree")
+    rdf = ROOT.RDataFrame(tree)
+    branchlist = ROOT.std.vector(ROOT.std.string)()
+    branchlist.push_back("tvector3")
+    rdf.Snapshot("tree", "tfile_with_tvector3_2.root", branchlist)
+    uproot.open("tfile_with_tvector3_2.root:tree").arrays()