error reporting: ROS_ERROR or error topic

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Thanks, I have come across diagnostics before, but have honestly been a bit confused about best practice. For example REP 107 states that is intended for reporting hardware data and errors. I was looking for something that reports errors in general...

... which might include that some user input was wrong, some file could not be found, etc.

(As you state) it also seems Diagnostics is intended for user info. I was thinking that reported errors could also be used as input to an error handler. A global place that could be configured to take certain actions if certain errors occurs. But this seems like misuse of Diagnostics?

I agree about it being a misuse of diagnotics when using this for error handling in code. I understand that diagnostics has been intended for HW mainly, but I think it is helpful in a lot of other places as well (as Long as it is about getting info to the user) (some might consider that misues too).

IMO, error handling should happen in the single nodes. So wrong user Input should be detected at the Moment of Input. Not existing files once you try to read/load them. And then the error should be produced in that node.

Maybe I am missing your Goal/idea why you want to have that centralized...

I was imagining any error referring so a globally defined error code. A configuration could then specify various handlers for each error code. E.g. a node emits an error about low disk space or high temperature for X. An error handler node decides the appropriate action.

These would seem to be largely application level and specific concerns, so creating an application specific implementation with topics and application-defined error codes with specific semantics seems justified.