TL;DR

• Updates the documentation for Tree.create_item(), Tree.set_columns() & Tree.clear()
• Adds error messages for Tree.create_item(), Tree.set_columns() & Tree.clear()
• Godot counterpart: Update the documentation for Tree.create_item(), Tree.set_columns() & Tree.clear() & add error messages. godotengine/godot#113178

This PR updates the documentation for Tree.create_item(), Tree.set_columns() & Tree.clear() & tells the user that all 3 methods can fail during mouse selection events. It also adds error messages for Tree.create_item(), Tree.set_columns() & Tree.clear()

The user will get the following error message if attempting to use any of the 3 methods during mouse selection events (Following RedMser's comment in godotengine/godot#105969 (review)):

(This is a test using the script provided by @kleonc in godotengine/godot#103101 (comment))

Text version:

E 0:00:02:715   tree.gd:14 @ _on_item_selected(): The tree cannot create items during mouse selection events.
  <C++ Error>   Condition "blocked > 0" is true. Returning: nullptr
  <C++ Source>  scene\gui\tree.cpp:5188 @ Tree::create_item()
  <Stack Trace> tree.gd:14 @ _on_item_selected()

(We use ERR_FAIL_COND_V_MSG instead of ERR_FAIL_COND_MSG here because Godot expects us to return a value or else we get build errors. We just return nullptr in this case.)

Summary by CodeRabbit

• Documentation

  • Updated Tree class documentation to reflect error conditions for item creation, clearing operations, and column modifications during mouse selection.

• Bug Fixes

  • Enhanced error reporting with descriptive messages when Tree operations fail during mouse selection events.