Multiple node trees datablocks and multiple file saves, open and closes causes deletion of node tree datablocks without warning

[axb2035]

Background: Most datablocks will be not be saved if there are no users linked (see here: https://docs.blender.org/manual/en/dev/data_system/data_blocks.html).

Crowdmaster node tree datablocks with a User Count of 0 are not written on save and purged on exiting a Blender session effectively deleting them forever like most other data blocks. Note there is a previous issue raised that unlinking a datablock does not reduce the user count for that session only and so may still be saved (#29).

Issue: If you create multiple Sim and/or Gen datablocks they will all save because of issue #29 even if unlinked. When you close and reload the file only the Sim or Gen datablock(s) displayed will not have a User count of 0. Any node trees you load into the node editor will also be updated and not have a 0 next to their name in the nodetree browser list. Any unloaded node trees will have a 0 next to their name in the node tree browser list from the datablock and will not be saved and are purged on exit 💥 😱

Steps to recreate: Step 1: Create two Sim node trees and two Gen node trees. In the node tree browser list they will not have 0 next to their name. Leave one of the node trees displayed (I have used Brain 2 in this example) and save file. Exit blender.

Step 2: Reopen blender file. In the node tree browser list the displayed node tree will not have 0 next to it's name. All the other Sim and Gen node trees will have 0 next to their name. Save file and exit Blender.

Step 3: Reopen file. Displayed node tree will remain - all other node trees will have been deleted

Step 4: Hope you have a backup!!! 😰

[Peter-Noble]

"Solved" by automatically setting the fake user on newly created node trees when the file is saved.