Commands: Allow bot to validate command arguments, and reflect on client

[ImpossibleReality]

Note: this is a continuation of #2452

The Problem

At the moment, it is really hard to do advanced validation of commands, and still imply that the command failed.
Although introducing a regex option would help, it still doesn't fully solve the problem.

The Scenario

I want to make a music bot, that plays music from youtube. Here is the structure for my command: /music name:string
When the user runs the command, I want to be able to tell the user if the bot was able to find the music they requested. If not, I want the command to error out.

My Proposal

After the client runs the command, discord will ask the bot for an interaction response. If the response has type 8 (or another number lol who cares) it is considered a validation error. The response MUST include a short description of the error (will be displayed in red text like when an interaction fails), and can optionally include a long description of the error, which will be included under the short description and the icon.

I also propose that error messages should be highlighted red, instead of purple (similar to how messages are highlighted orange when you are mentioned).

[sm0lvoicc]

welp i have a very similar fr, this tbh

[SlipperySpelunky]

Better to give us access to Discord's client-side command validation to create our own custom argument types, so we can prevent the user from executing the command in the first place

[ImpossibleReality]

Although that would be ideal, there would be the worry of ReDos-ing the client, and hogging cpu/memory. A workaround to that would be something like re2, which doesn't support backtracking.

[WilsontheWolf]

I've been using just empheral messages and it works fine for most cases. You can use emoji, embeds and whatnot just fine.

[ImpossibleReality]

The whole point is to tell not only the user, but also discord that a command failed. Although an emoji/embed works, it's not ideal.

[ImpossibleReality]

It's like having an error message in a web app colored blue when other error messages are colored red in your app, it works, but it could be improved upon.

[WilsontheWolf]

I mean sure but this means you need to store more info on discord with info about the error (which as far as I know doesn't exist) and update all the clients to add this. Also if your bot is always online and handles all errors the errors will be constant across your bot.

[ImpossibleReality]

I'm a little confused about what you mean by storing info on discord, since error messages would have to be ephemeral (you don't want everybody knowing that you made a typo in your command), and therefore nothing should be stored on discord, and client updates shouldn't hinder adding a new feature. Also, this isn't about error handling it is about command argument validation, ie making sure that the user enters something that the bot can understand

[elkowar]

I'd love this, too. Discord already has UX for "invalid argument", and I hate how inconsistent it gets as soon as I introduce additional validation on top of that. With the autocomplete system we already have an existing precedent for discord sending the content of an argument before the command is submitted, so clearly that's not an inherent consern.

The optimal solution here would be for discord to allow me to register bot-side argument validation somehow, such that when the user tries to submit his command / finish typing an argument, I can look at the argument values and say "ahh, that one is invalid, here's a short description of why".

I'd argue that most bots have lots of cases of additional argument validation being necessary, i.e. for commands taking a duration (needs to be parsed and then validated), Commands that require valid URLs, etc.
There's been a lot of feature requests about the addition of specific, new command option types, i.e. #3292 #4891 #3918 #3293 #4108
Regex-based validation would be a (worse) alternative, that would still help a lot. Re2 not being directly available for browsers is obviously an issue here (even though technically alternatives like this exist), and said regex validation could also be done on discords server-side via re2 -- I think just letting the bot itself do proper, fully flexible argument validation would be a huge improvement to UX here.

I mainly think the UX currently suffers from this for two reasons:

• it's inconsistent. Getting "invalid argument" when you put in a string where it wants a number is nice! Getting an ephemeral bot response to an invalid argument really isn't remotely as pretty, and the inconsistency is somewhat confusing to users
• Running a command with an invalid argument, then getting an ephemeral "invalid duration" or whatever response, is massively inconvenient to the user w.r.t. re-trying the command. currently, if you want to copy-paste your old bot command invocation, that requires a minimum of 5-6 steps (open the popup, select text, copy text, paste text, fix argument, rerun command) -- which could be massively improved with proper, bot-side validation!