While working on issue #3435 <https://github.com/leo-editor/leo-editor/issues/3435>, I see that *u.saveTree* can't possibly work! About a dozen commands and methods call u.saveTree indirectly. Undo and redo for these may be dangerous!
This Engineering Notebook post discusses what to do about this situation. *tl;dr:* See the summary. *The problem* A cff shows that about a dozen commands and script helpers call *u.beforeChangeTree* and *u.afterChangeTree*. Both these methods call *u.saveTree(p)*. Alas, *u.saveTree has no chance of working*. As a result, Leo's undo logic is dangerously flawed in about a dozen places. The section *<< about u.saveTree >> *discusses* u.createVnodeUndoInfo*, u.saveTree's helper. These comments do not describe u.createVnodeUndoInfo correctly. Worse, u.createVnodeUndoInfo itself has no chance of solving the original problem! Details omitted. *Solutions* Imo, the following commands should *not *be undoable: *refresh-from-disk*, *read-at-auto-nodes*, r*ead-at-file-nodes*, and *read-at-shadow-nodes*. These commands are "one-way" updates. Rewriting their undo code would be fraught. Bugs in the undo/redo logic could be devastating. Various commands and methods create a single new node. Their undo logic can mimic that of undo/redo insert-node. Undoing these commands would delete the newly-created node. Redo would undo the delete. The *abbrev.expand_tree *method might be a unique case. I'm not yet sure what to do. *Summary* - We must retire u.saveTree, u.beforeChangeTree, and u.afterChangeTree. - Several commands should *not* be undoable. - Commands that insert a single node can use the undo/redo logic of insert-node. All of your comments are welcome. Edward -- You received this message because you are subscribed to the Google Groups "leo-editor" group. To unsubscribe from this group and stop receiving emails from it, send an email to leo-editor+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/leo-editor/d6c73820-9ac1-4669-8778-02351f588825n%40googlegroups.com.
