Idea: Warning developer of invalid component state

[droqen]

Example situation: the local_to_parent component fails to perform its function when certain conditions are not met. (Hierarchy must be set up correctly, parent must have local_to_world component.)

Currently, there is no feedback to the developer about this.

As one suggestion, we could work towards something like what Godot has, which I'll show below:

fig. 1

In figure 1, CharacterBody2D_a is set up correctly, while CharacterBody2D_b is not.

Clicking on the small /!\ icon displays a popup:

fig. 2

Figure 2 shows the popup message: it indicates what's causing the problem, what the consequences of the problem are, and suggests a way to fix it. If the developer runs the program anyway, there are no further error messages or warnings.

We don't currently have a graphical UI for editing nodes, so my initial proposal is this:

1. Some kind of common system for each component to detect and report any invalid state which causes it not to function (e.g. a local_to_parent child that is missing a parent, or its parent does not have the local_to_world component)

2. When running in non-debugger mode, print this warning to console and suggest the game be run in --debugger mode to examine these errors/warnings better.

3. In --debugger mode, show something similar to the Godot /!\ icon next to every component that is reporting invalid state.

Related to #480