Remora.Discord.Commands 26.2.3

Remora.Discord.Commands

This package provides glue code for using Remora.Commands with Remora.Discord, adding appropriate conditions, autocompletion, type parsers, and uniform UX for Remora-based applications.

Structure

Most of the library's functionality is offloaded to Remora.Commands, for which documentation is available at its repository. Beyond this, the structure of the library revolves around concepts that should be relatively familiar to users of other Discord libraries.

Take a look in Parsers for an overview of the various types supported as first-class parameters, beyond what Remora.Commands provides out of the box.

For each command interaction that is received by your application, a matching appropriate command is identified in your registered command trees, and is executed with an implementation of ICommandContext, which provides contextual information about the command environment (such as guilds, users, additional data payloads, etc).

Furthermore, any autocompletion requests are routed to implementations of IAutocompleteProvider, enabling you to provide bot-driven autocompletion of command parameters.

Usage

To enable commands, call the following method on your dependency injection container.

services.AddDiscordCommands(enableSlash: true);

Note that slash commands are not enabled by default, and you must opt into them by passing true as above.

Registering slash commands

Once you've added the command services and instantiated your service container, you must register your command tree(s) with Discord.

Inject or retrieve the SlashService from your container in an appropriate way, and then call

await slashService.UpdateSlashCommandsAsync();

This will register the default command tree globally; optionally, you may register a different named tree, or register the tree at a guild level.

await slashService.UpdateSlashCommandsAsync(guildID: myServerID, treeName: myTreeName);

Not every feature supported by Remora.Commands is supported by Discord - if you end up using incompatible features, an exception will be thrown at this point.

Special Attributes

Remora.Discord.Commands exposes a number of attributes you can use to influence or configure the way your commands are translated to Discord's slash command UX.

For the most part, these attributes map directly to fields or properties on Discord's application command object, but some have more specialized uses.

ChannelTypes

Sets the channel types that should be show in Discord's autocompletion when a user is typing.

Can be applied to Snowflake or IPartialChannel (and implementors)-typed command parameters.

DiscordDefaultDMPermission

Sets the default DM accessibility for a group or command.

Can be applied to top-level groups or commands. The attribute is not compatible with nested groups or commands, and will produce an exception if applied to those.

DiscordDefaultMemberPermissions

Sets the default member permissions required for a user to use a group or command.

Can be applied to top-level groups or commands. The attribute is not compatible with nested groups or commands, and will produce an exception if applied to those.

DiscordNsfw

Sets whether the group or command is age-restricted and hidden or otherwise made unavailable in open channels.

Can be applied to top-level groups or commands. The attribute is not compatible with nested groups or commands, and will produce an exception if applied to those.

DiscordTypeHint

Hints Discord's autocompletion about the type of the parameter it is applied to, allowing only certain types of autocompleted input data.

Can be applied to any parameter, but is typically most useful for Snowflake-typed parameters.

ExcludeFromChoices

Removes the marked enumeration member from Discord's autocomplete list.

Can be applied to enumeration members.

ExcludeFromSlashCommands

Excludes the marked group or command from the slash command UI. This is primarily useful when you have certain commands which use incompatible Remora.Commands features, since it also removes all restrictions that would otherwise come from being a slash command.

Can be applied to groups and commands.

MinValue

Marks a numeric parameter as having a minimum allowed value. This restricts Discord's autocompletion and client-side validation to the specified range.

The range is inclusive.

Can be applied to any parameter which has a numeric C# type.

MaxValue

Marks a numeric parameter as having a maximum allowed value. This restricts Discord's autocompletion and client-side validation to the specified range.

The range is inclusive.

Can be applied to any parameter which has a numeric C# type.

SuppressInteractionResponse

This attribute prevents Remora from automatically sending an interaction response on your behalf when receiving a slash command (or similar interaction, such as a context menu click or button press). If you suppress the response, you must send one yourself within a few seconds of entering user code or Discord will consider the interaction failed.

Can be applied to groups and commands.

Context Menu Commands

Discord also supports context menu items on users and messages, which are treated as special slash commands by their system.

These commands have some additional restrictions.

• they must have a particular C# signature
• they must be declared as top-level commands
• they must not have descriptions

To mark a command as either a User or a Message command, apply the CommandType attribute.

A User command must take a single parameter named user. A Message command must take a single parameter named message.

In both cases, the data passed to the command will be a string containing the user or message's ID; typically, this means you'd want to declare the parameter with a type that can parse this ID into the entity you want. IUser or IMessage is probably a good bet, but you can use any type you want as long as its parser understands a Snowflake in string form.

Context menus also have relaxed rules when it comes to command names, and you can use both varied capitalization as well as whitespace.

[Command("My User Command")]
[CommandType(ApplicationCommandType.User)]
public async Task<IResult> MyUserCommand(IUser user)
{
    // ...
}

User Feedback

If you want to create messages with a uniform UX, you may use the FeedbackService for various message types, such as notices, successes, failures, etc. The styling of these messages is controlled by an IFeedbackTheme, of which there are two provided by default. These themes map to Discord's own dark and light themes, respectively.

You may also implement your own theme and register it with the dependency injection container.

Autocomplete

To provide autocomplete options while users of your application type, create a class that implements either IAutocompleteProvider<T> (for autocompletion of specific parameter types) or IAutocompleteProvider (for generic autocompletion).

public class MyAutocompleteProvider : IAutocompleteProvider
{
    public string Identity => "autocomplete::my-provider";
    
    public ValueTask<IReadOnlyList<IApplicationCommandOptionChoice>> GetSuggestionsAsync
    (
        IReadOnlyList<IApplicationCommandInteractionDataOption> options,
        string userInput,
        CancellationToken ct = default
    )
    {
        // ...
    }
}

You may suggest up to 25 choices when your provider is invoked.

In order to select which autocomplete provider to use, apply the AutocompleteAttribute to the appropriate parameters in your command groups. If you're using the type-specific autocomplete provider, this is not required.

Preparation error events

If a command can't be successfully prepared from whatever the user sends (due to malformed input, parsing failures, failed conditions etc.), the command's "preparation" is considered failed.

In many cases, it's useful to hook into this event in order to provide the end user with helpful information about what they did wrong or why the command didn't work.

This can be accomplished by registering a preparation error event, which is a class that implements IPreparationErrorEvent.

public class MyPreparationErrorEvent : IPreparationErrorEvent
{
    public Task<Result> PreparationFailed(IOperationContext context, IResult preparationResult, CancellationToken ct = default)
    {
        // ...
    }
}

...

services.AddPreparationErrorEvent<MyPreparationErrorEvent>();

The preparation result contains information about the error - try checking for things like CommandNotFoundError or ParameterParsingError when you get a preparation error.

If you return an error in a preparation error event, the command invocation is cancelled, and never progresses to the real execution stage.

By default, user- or environment-caused preparation errors don't produce any log messages or user-facing output. It's up to you to decide if and how you want to handle these.

Note that if you register multiple preparation events, they will run sequentially within the same service scope. Order is not guaranteed, but typically ends up being the same as registration order. Every event will get a chance to run even if one of them fails, but failure of any of the events is considered a collective failure, and will cause the command invocation to be cancelled.

Pre- and post-execution events

In some cases, it may be useful to execute pieces of code before or after invocation of a command (checking GDPR consent, logging error messages, etc).

This can be accomplished by registering pre- and post-execution events, which are classes which implement either IPreExecutionEvent or IPostExecutionEvent, respectively.

public class MyPreExecutionEvent : IPreExecutionEvent
{
    public Task<Result> BeforeExecutionAsync(ICommandContext context, CancellationToken ct = default)
    {
        // ...
    }
}

...

services.AddPreExecutionEvent<MyPreExecutionEvent>();

If you return an error in a pre-execution event, the command invocation is cancelled, and never progresses to the real execution stage. If you return an error in a post-execution event, this is treated as if the command itself had failed, which may be useful for things like scrubbing database transactions.

Note that if you register multiple pre- or post-execution events, they will run sequentially within the same service scope. Order is not guaranteed, but typically ends up being the same as registration order. Every event will get a chance to run even if one of them fails, but failure of any of the events is considered a collective failure. In the case of pre-execution events, this will cause the command invocation to be cancelled.