Fix midmeasure clef export regression involving voices

music21/musicxml/m21ToXml.py

@@ -3113,8 +3113,8 @@ def parseFlatElements(self, m, *, backupAfterwards=False):
             amountToMoveForward = int(round(divisions * (groupOffset
                                                              - self.offsetInMeasure)))
             if amountToMoveForward > 0 and any(
-                    isinstance(obj, note.GeneralNote) for obj in objGroup):
-                # gap in stream between GeneralNote objects: create <forward>
+                    isinstance(obj, (note.GeneralNote, clef.Clef)) for obj in objGroup):
+                # gap in stream between GeneralNote/Clef objects: create <forward>
                 mxForward = Element('forward')
                 mxDuration = SubElement(mxForward, 'duration')
                 mxDuration.text = str(amountToMoveForward)

music21/musicxml/testPrimitive.py

@@ -18236,6 +18236,30 @@ def testMidMeasureClefs2(self):
         self.assertEqual([c.classes for c in new_clefs],
                          [c.classes for c in orig_clefs])
 
+    def testMidMeasureClefs3(self):
+        '''
+        Test midmeasure clef changes outside voices
+        '''
+        from music21 import clef
+        from music21 import note
+        from music21 import musicxml
+        from music21 import stream
+
+        v1 = stream.Voice()
+        v2 = stream.Voice()
+        quarter = note.Note()
+        v1.repeatAppend(quarter, 4)
+        v2.repeatAppend(quarter, 4)
+        m = stream.Measure([v1, v2])
+        m.insert(1.0, clef.BassClef())
+        p = stream.Part(m)
+        p.makeNotation(inPlace=True)
+
+        tree = musicxml.test_m21ToXml.Test().getET(p)
+        self.assertEqual(len(tree.findall('.//clef')), 1)
+        # One backup from the clef back to voice 1, then another back to voice 2
+        self.assertEqual(len(tree.findall('.//backup')), 2)
+
 # ------------------------------------------------------------------------------