prepend keeps index of existing handler, or jumps ahead of aos handlers (_eval, and _default)

[dtfiedler]

When a handler previously exists via Handler.add, Handler.append etc, and then is modified to Handler.prepend it's current index is preserved, making it only prepend the handlers that follow in the ordered Handler list. This seems counterintuitive when iterating on handlers and electing to move a handler up in the Handlers.list. Additionally, when a prepended handlers is introduced, it is place in first index of the Handlers list which could jump over any default handlers provided by AOS. This seems particularly risky in the case of _eval where one could brick a process by prepending a handler before _eval with bad code, and then having no way to replace the code out of it.

A few thoughts:

• aos provided handlers by default, should remaining beginning of the Handlers list (e.g. _default, _eval, etc. are always the first handlers)
• Handlers.prepend should move a handler to after the private handlers (_eval and _default) unless explicitly stated to keep it's current position or to be placed higher than the private ones

Related code: https://github.com/permaweb/aos/blob/main/process/handlers.lua#L107-L114

[twilson63]

Great points, maybe _default and _eval should be removed from handlers list and implictly applied.

handle
_eval

...

for each
handlers.list
end

...

_default

end

---

re-updating handlers pattern and handle function if already exists is by design, whether you call prepend, add, etc. Not sure if it makes sense to change this, it is built this way so developers can re-eval their scripts, seems to work for many.

[dtfiedler]

I like the idea of them being implicit, seems sensible - with that change, would you consider not allowing Handlers with those names to avoid overriding them?

I also understand not wanting to update the handler patterns, but would suggest at the very least additional documentation around the behavior if they already exist. this behavior surprised us when we realized the handler we moved to prepend did not change positions in the list and only executed before later handlers.

I can make an initial PR to the docs - mind pointing me to the correct spot?

[twilson63]

https://cookbook_ao.g8way.io/references/handlers.html