In my Godot project I have a UI panel that displays data derived from a Resource.
To be able to see how it looks immediately in the editor, I tagged it with @tool.
But I started seeing errors like this:
Invalid call. Nonexistent function ...
The errors came whenever I tried to call the members of a custom object I fished from the scene. I decided to try with a development version, and the error became this:
Invalid call. Nonexistent function ... Attempt to call a method on a placeholder instance.
What is going on?
I ran git blame on the line where the Attempt to call a method on a placeholder instance.-message was recently added. It led me to this commit https://github.com/godotengine/godot/commit/2d8f6c1b1d984222d1690f8afd504faed9f303be. The commit message says:
GDScript: Fix message when calling non-tool function in tool mode.
So the problem was that I was invoking code from a script without the @tool-attribute when running the tool script. (In my case, a member function on a child panel of the main panel.) I added the tool attribute to the child panel and the error went away. It seems the attribute needs to be applied transitively to all code invoked at editor time. I suppose that makes sense.