Fix unlink block by reusing existing code

engine/api.py

@@ -897,11 +897,23 @@ def unlinkCurrentBlock():
 
 def unlinkBlock(blockId):
     track, block = session.data.blockById(blockId)
-    newData = block.getUnlinkedData()
-    assert newData
-    _setBlockData(block, newData) #handles undo and callbacks
+    #if len(block.linkedContentBlocks) == 1: return  #This will not work because block is still the old one. unlink replaces with a standalone copy but we keep the original for undo.
 
+    with session.history.sequence("unlink block"):
+        duplicateBlock(blockId)
+        deleteBlock(blockId) #original one
+    callbacks._historyChanged()
+
+    #Does not work properly:
+    #newData = block.getUnlinkedData()
+    #assert newData
+    #_setBlockData(block, newData) #handles undo and callbacks
+
+#deprecated
 def _setBlockData(block, newData):
+    """DEPRECATED. This did not work. The linked blocks were not reduced.
+    At point of the bug reports, instead of fixing this, we used
+    duplicate block and delete which already provides all functionality"""
     session.history.register(lambda bl=block, old=block.data: _setBlockData(bl, old), descriptionString = "set block data")
     block.data = newData
     #no callbacks needed.

engine/block.py

@@ -167,7 +167,10 @@ class Block(object):
         return new
 
     def getUnlinkedData(self):
-        """Set and handled for undo/redo by the api"""
+        """
+        Returns a new list with copies of items.
+        Set and handled for undo/redo by the api.
+        """
         newData = []
         newParentBlocks = WeakSet()
         newParentBlocks.add(self)

engine/track.py

@@ -436,6 +436,7 @@ class Track(object):
         return new
 
     def appendExistingBlock(self, block):
+        assert type(block) is Block, block
         block.parentTrack = self
         self.blocks.append(block)
 

template/engine/history.py

@@ -69,7 +69,7 @@ class History(object):
     def sequence(self, descriptionString):
         """Convenience function. All registrations from now on will be undone at once.
         call stopSequence when done.
-        This is not meant for high level scripts and not for user-interaction.
+        This is meant for high level scripts and not for user-interaction.
 
         This context can also be used to force a custom name for the undo description, even if it is
         only one step.