Don't export empty tracks (no duration items) to Lilypond

engine/block.py

@@ -344,6 +344,16 @@ class Block(object):
     def isAppending(self):
         return self.localCursorIndex == len(self.data) #len counts from 1 and the cursorIndex from 0. So if they are the same we are one cursor position right of last item
 
+    def zeroLogicalDuration(self)->bool:
+        """Return true if this has no actual items with duration in it.
+        A block with only text items and barlines is empty.
+        Minimum tick duration does not affect isEmpty"""
+        for item in self.data:
+            if item.logicalDuration() > 0:
+                return False
+        return True
+
+
     def lilypond(self, carryLilypondRanges):
         """Called by track.lilypond(), returns a string.
         carryLilypondRanges is handed from item to item for ranges

engine/main.py

@@ -917,6 +917,8 @@ class Data(template.engine.sequencer.Score):
             return False
 
         for block in startBlock.linkedContentBlocks: #all linked blocks in all tracks, including currentBlock. All blocks are unique. The content is not.
+            if not block.parentTrack:
+                continue #hotfix 2022-08-05. It was "None" . #TODO maybe from deleting a link previously that was in multiple tracks?
             blockIndex = block.parentTrack.blocks.index(block)
             try:
                 followUpBlock = block.parentTrack.blocks[blockIndex +1]
@@ -1006,7 +1008,7 @@ class Data(template.engine.sequencer.Score):
             newLeft.name = block.name
             newLeft.minimumInTicks = block.minimumInTicks / 2
             assert newLeftId in Block.allBlocks
-            assert newLeft.parentTrack is block.parentTrack
+            #assert newLeft.parentTrack is block.parentTrack #that is just not true. We have linked blocks in other tracks as well.
             assert newLeft in protoBlockLeft.linkedContentBlocks
 
             newRight = protoBlockRight.contentLink()
@@ -1014,7 +1016,7 @@ class Data(template.engine.sequencer.Score):
             newRight.name = block.name
             newRight.minimumInTicks = newLeft.minimumInTicks
             assert newRightId in Block.allBlocks
-            assert newRight.parentTrack is block.parentTrack
+            #assert newRight.parentTrack is block.parentTrack
             assert newRight in protoBlockRight.linkedContentBlocks
 
             positionToInsert = blockOrder.index(id(block))
@@ -1088,9 +1090,9 @@ class Data(template.engine.sequencer.Score):
         Each object controls what it exports. Overrides are possible at every level.
         """
         tempoStaff = self.tempoTrack.lilypond() if "metronome" in self.metaData and self.metaData["metronome"] else ""
-        data = {track:track.lilypond() for track in self.tracks} #processed in the lilypond module
+        data = {track:track.lilypond() for track in self.tracks if not track.zeroLogicalDuration() } #processed in the lilypond module
         #the template file name is in metadata, but it can be empty or not existient
-        #From Template has direct access to the score metadata and WILL destructively modify it's own parameters, like the lilypond template entry.
+        #From Template has direct access to the score metadata and WILL destructively modify it's own parameters, like the "lilypond template" entry itself.
         return fromTemplate(session = self.parentSession, data = data, meta = self.metaData, tempoStaff = tempoStaff)
 
 

engine/track.py

@@ -846,6 +846,15 @@ class Track(object):
         #we don't need to unregister anything from cbox.
 
 
+    def zeroLogicalDuration(self)->bool:
+        """Return true if this has no actual items with duration in it.
+        A track with only text items and barlines is empty.
+        Minimum tick duration does not affect isEmpty"""
+        for block in self.blocks:
+            if not block.zeroLogicalDuration():
+                return False
+        return True
+
     #Save / Load / Export
     def lilypond(self):
         """Called by score.lilypond(), returns a string.