tree_mode toggle doesn't fully restore tree state (save_tree)

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Summary

When save_tree=True, toggling tree_mode OFF→ON should restore the saved tree state (collapsed groups, expanded folders, group_by). However, the restoration is inconsistent.

Current Behavior

• ✅ Works: Make changes → toggle OFF → toggle ON → state restored
• ❌ Doesn't work: Toggle OFF → toggle ON (no changes) → state lost

Root Cause Analysis

Two design issues identified in update_tree_mode() and load_state():

1. Timing dependency

load_state() validates saved groups against tree_state.groups (line 96 in tree.py):

existing_groups = set(self.groups)
if v and v in existing_groups:  # validation fails if groups is empty

But groups is only populated by update_tree(). The order matters:

• ❌ load_state() → update_tree() (groups empty during validation)
• ✅ update_tree() → load_state() (groups populated)

2. group_by restoration side effects

When load_state() restores a different group_by, it triggers update_group_by() which:

1. Clears collapsed_groups and expanded_folders
2. Calls tree.update()

The collapsed_groups restoration happens AFTER this in load_state(), so it should work. But the interplay is fragile.

Partial Fix Applied

Commit ac15bcd improves some cases by:

• Calling update_tree() before load_state()
• Saving state when tree_mode is turned OFF

Suggested Full Fix

Consider refactoring to separate concerns:

1. Tree building: Always done by update_tree(), populates structure
2. State restoration: Done after tree is built, only affects collapse/expand state
3. Persistence: Save on any state change, not just on toggle OFF

This may require changes to:

• prefs/tree.py: TreeState, load(), save()
• preferences.py: update_tree_mode(), update_group_by()

Related Files

• preferences.py: update_tree_mode() (line ~531)
• prefs/tree.py: TreeState.load(), TreeState.save()

Labels

• bug
• tree-view
• low-priority

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Related Commits

• ac15bcd - Partial fix: call update_tree() before load_state(), save on toggle OFF
• 70d6255 - TreeState class access fix (earlier in this session)
• c221dd4 - P7-P8 context_menu.py and operators.py

The partial fix is in the pme2-dev branch.