Avoid altering score on write

makeRests was called inPlace before copies were made.

See cuthbertLab#1557

music21/musicxml/m21ToXml.py

@@ -496,12 +496,13 @@ def fromGeneralObject(self, obj: prebase.ProtoM21Object):
         outObj = None
 
         if isinstance(obj, stream.Stream) and self.makeNotation:
-            obj.makeRests(refStreamOrTimeRange=[0.0, obj.highestTime],
-                          fillGaps=True,
-                          inPlace=True,
-                          hideRests=True,  # just to fill up MusicXML display
-                          timeRangeFromBarDuration=True,
-                          )
+            # This is where the first (and hopefully only) copy is made.
+            obj = obj.makeRests(refStreamOrTimeRange=[0.0, obj.highestTime],
+                                fillGaps=True,
+                                inPlace=False,
+                                hideRests=True,  # just to fill up MusicXML display
+                                timeRangeFromBarDuration=True,
+                                )
 
         for cM, methName in self.classMapping.items():
             if cM in classes:
@@ -517,14 +518,14 @@ def fromGeneralObject(self, obj: prebase.ProtoM21Object):
 
     def fromScore(self, sc):
         '''
-        Copies the input score and runs :meth:`~music21.stream.Score.makeNotation` on the copy.
+        Runs :meth:`~music21.stream.Score.makeNotation` on the copy.
         '''
-        scOut = sc.makeNotation(inPlace=False)
-        if not scOut.isWellFormedNotation():
-            warnings.warn(f'{scOut} is not well-formed; see isWellFormedNotation()',
+        sc.makeNotation(inPlace=True)
+        if not sc.isWellFormedNotation():
+            warnings.warn(f'{sc} is not well-formed; see isWellFormedNotation()',
                 category=MusicXMLWarning)
-        # scOut.makeImmutable()
-        return scOut
+        # sc.makeImmutable()
+        return sc
 
     def fromPart(self, p):
         '''
@@ -548,20 +549,20 @@ def fromMeasure(self, m):
         solutions in Part or Stream production.
         '''
         m.coreGatherMissingSpanners()
-        mCopy = m.makeNotation()
-        if mCopy.style.measureNumbering is None:
+        m.makeNotation(inPlace=True)
+        if m.style.measureNumbering is None:
             # Provide a default
-            mCopy.style.measureNumbering = 'measure'
+            m.style.measureNumbering = 'measure'
         clef_from_measure_start_or_context = m.getContextByClass(
             clef.Clef,
             getElementMethod=common.enums.ElementSearch.AT_OR_BEFORE_OFFSET
         )
         if clef_from_measure_start_or_context is None:
-            mCopy.clef = clef.bestClef(mCopy, recurse=True)
+            m.clef = clef.bestClef(m, recurse=True)
         else:
-            mCopy.clef = clef_from_measure_start_or_context
+            m.clef = clef_from_measure_start_or_context
         p = stream.Part()
-        p.append(mCopy)
+        p.append(m)
         p.metadata = copy.deepcopy(getMetadataFromContext(m))
         context_part = m.getContextByClass(stream.Part)
         if context_part is not None: