report a command system origin in case of panic

[mockersf]

related to #1743 and #2219

Add a new feature bevy_command_panic_origin. If it is enabled, the command system origin will be logged in case of panic when applying it.

This is not meant to be a final feature with nice UX but more a stepping stone for adding proper result handling of commands. But it can be useful as is, and adding error to all commands is a much larger change #2004

[NathanSWard]

Should this be Option<_>?
inside fn init system_name is always set as Some.

[mockersf]

the struct CommandQueue is pub and can be built using default() (done in LightsNode and in RenderResourcesNode). In those case a None is better than an empty string I think.

Though with the field behind a feature it's less of an issue I guess

[NathanSWard]

Could we just impl Default for CommandQueue?

[NathanSWard]

Unless it's actually possible for it to be None...

[mockersf]

It can be None!

[MinerSebas]

The new feature also needs to be mentioned in the ./docs/cargo_features.md file.

[NathanSWard]

@mockersf
Curious on what your thoughts are with this and how #2241 interact?
Specifically because my PR changes the default behavior to not panic, so the panic handler would only work where someone specifies

.on_err(CommandErrorHandler::panic())

which, I have a feeling will be few and far between.

It's probably a better approach to have the Command trait be defined as something like:

struct CommandArgs<'a> {
    world: &'a mut World,
    system_name: Cow<'static, str>,
}

trait Command  {
    fn write(self: Box<Self>, args: CommandArgs);
}

So that way all commands (and error handlers) can have the system name correctly propagated to them?

[mockersf]

Curious on what your thoughts are with this and how #2241 interact?

I think this'll definitely to be looked at after #2241 has been merged, moved it to draft

It's probably a better approach to have the Command trait be defined as something like:

struct CommandArgs<'a> {
    world: &'a mut World,
    system_name: Cow<'static, str>,
}

trait Command  {
    fn write(self: Box<Self>, args: CommandArgs);
}

So that way all commands (and error handlers) can have the system name correctly propagated to them?

Or having the system name in the CommandError struct?

[NathanSWard]

Or having the system name in the CommandError struct?

Yep, it'll be there to.
However, to have it even be passed to the error handler, it needs to be passed though to Command::write as well.