[Bug]: Parameters in Slash Commands do not pass attributes in Autocomplete Handlers

[Andrei-Marcu]

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Description

When defining a slash command, attributes applied to the parameter are not passed to the Autocomplete Handler.

Steps to Reproduce:

1. Define a slash command with and apply an attribute to it.

[SlashCommand("test", "Desc")]
public Task Test([CustomAutocomplete("option1", "option2")] string parameter)

2. Attempt to access the attribute of the parameter within an AutocompleteHandler.

public class CustomAutocompleteAttribute : AutocompleteAttribute
{
    internal readonly string[] _options;

    public CustomAutocompleteAttribute(params string[] options) : base(typeof(CustomAutocompleteHandler))
    {
        _options = options;
    }
}

public class CustomAutocompleteHandler : AutocompleteHandler
{
    public override async Task<AutocompletionResult> GenerateSuggestionsAsync(IInteractionContext context, IAutocompleteInteraction autocompleteInteraction, IParameterInfo parameter, IServiceProvider services)
    {
        var attribute = (CustomAutocompleteAttribute)parameter.Attributes.Single(a => a is CustomAutocompleteAttribute); //Throws, and Actually parameter.Attributes is empty

        var options = attribute._options;

        //code

        return AutocompletionResult.FromSuccess(/*results*/);
    }
}

Based on what I gathered, I've seen only the Optional Attribute to get passed, either when it is explicitly put or when the parameter is defined with a default like string parameter = ""

Version

3.17.0

Working Version

No response

Logs

nothing extra in logs besides the single assertion throwing

Sample

No response

Packages

not applicable

Environment

• Windows 10 22H2 x64
• .NET 8.0

[Andrei-Marcu]

Based on further testing I found out that certain attributes and their subtypes don't get passed down to AutocompleteHandler, AutocompleteAttribute being one of them.

To get around this, defining a separate attribute to contain the data works, but I find it inelegant:

[SlashCommand("test", "Desc")]
public Task Test([Autocomplete<CustomAutocompleteHandler>,  Custom("option1", "option2")] string parameter)

[AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false)]
public class CustomAttribute : Attribute
{
    internal readonly string[] _options;

    public CustomAttribute(params string[] options)
    {
        _options = options;
    }
}

public class CustomAutocompleteHandler : AutocompleteHandler
{
    public override async Task<AutocompletionResult> GenerateSuggestionsAsync(IInteractionContext context, IAutocompleteInteraction autocompleteInteraction, IParameterInfo parameter, IServiceProvider services)
    {
        var attribute = (CustomAttribute)parameter.Attributes.Single(a => a is CustomAttribute);
        var options = attribute._options;

        //code

        return AutocompletionResult.FromSuccess(/*results*/);
    }
}