Add ChoiceParameter trait instead of direct impls

Fixes serenity-rs#126

examples/fluent_localization/main.rs

@@ -24,6 +24,8 @@ pub async fn welcome(
     user: serenity::User,
     message: WelcomeChoice,
 ) -> Result<(), Error> {
+    use poise::ChoiceParameter as _;
+
     ctx.say(format!("<@{}> {}", user.id.0, tr!(ctx, message.name())))
         .await?;
     Ok(())

macros/src/choice_parameter.rs

@@ -64,33 +64,10 @@ pub fn choice_parameter(input: syn::DeriveInput) -> Result<TokenStream, darling:
     }
 
     let enum_ident = &input.ident;
-    let indices = 0_u64..(variant_idents.len() as _);
+    let indices = 0..variant_idents.len();
     Ok(quote::quote! {
-        #[poise::async_trait]
-        impl poise::SlashArgument for #enum_ident {
-            async fn extract(
-                _: &poise::serenity_prelude::Context,
-                _: poise::ApplicationCommandOrAutocompleteInteraction<'_>,
-                value: &poise::serenity_prelude::json::Value,
-            ) -> ::std::result::Result<Self, poise::SlashArgError> {
-                use poise::serenity_prelude::json::prelude::*;
-                let choice_key = value
-                    .as_u64()
-                    .ok_or(poise::SlashArgError::CommandStructureMismatch(
-                        "expected u64",
-                    ))?;
-
-                match choice_key {
-                    #( #indices => Ok(Self::#variant_idents), )*
-                    _ => Err(poise::SlashArgError::CommandStructureMismatch("out of bounds choice key")),
-                }
-            }
-
-            fn create(builder: &mut poise::serenity_prelude::CreateApplicationCommandOption) {
-                builder.kind(poise::serenity_prelude::CommandOptionType::Integer);
-            }
-
-            fn choices() -> Vec<poise::CommandParameterChoice> {
+        impl poise::ChoiceParameter for #enum_ident {
+            fn list() -> Vec<poise::CommandParameterChoice> {
                 vec![ #( poise::CommandParameterChoice {
                     name: #names.to_string(),
                     localizations: std::collections::HashMap::from([
@@ -99,40 +76,30 @@ pub fn choice_parameter(input: syn::DeriveInput) -> Result<TokenStream, darling:
                     __non_exhaustive: (),
                 }, )* ]
             }
-        }
-
-        impl std::str::FromStr for #enum_ident {
-            type Err = poise::InvalidChoice;
 
-            fn from_str(s: &str) -> ::std::result::Result<Self, Self::Err> {
-                #(
-                    if s.eq_ignore_ascii_case(#names)
-                        #( || s.eq_ignore_ascii_case(#alternative_names) )*
-                    {
-                        Ok(Self::#variant_idents)
-                    } else
-                )* {
-                    Err(poise::InvalidChoice { __non_exhaustive: () })
+            fn from_index(index: usize) -> Option<Self> {
+                match index {
+                    #( #indices => Some(Self::#variant_idents), )*
+                    _ => None,
                 }
             }
-        }
 
-        impl std::fmt::Display for #enum_ident {
-            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-                f.write_str(self.name())
+            fn from_name(name: &str) -> Option<Self> {
+                #( if name.eq_ignore_ascii_case(#names)
+                    #( || name.eq_ignore_ascii_case(#alternative_names) )*
+                {
+                    return Some(Self::#variant_idents);
+                } )*
+                None
             }
-        }
 
-        impl #enum_ident {
-            /// Returns the non-localized name of this choice
-            pub fn name(&self) -> &'static str {
+            fn name(&self) -> &'static str {
                 match self {
                     #( Self::#variant_idents => #names, )*
                 }
             }
 
-            /// Returns the localized name for the given locale, if one is set
-            pub fn localized_name(&self, locale: &str) -> Option<&'static str> {
+            fn localized_name(&self, locale: &str) -> Option<&'static str> {
                 match self {
                     #( Self::#variant_idents => match locale {
                         #( #locales => Some(#localized_names), )*

macros/src/command/slash.rs

@@ -92,6 +92,7 @@ pub fn generate_parameters(inv: &Invocation) -> Result<Vec<proc_macro2::TokenStr
             false => quote::quote! { None },
         };
         // TODO: theoretically a problem that we don't store choices for non slash commands
+        // TODO: move this to poise::CommandParameter::choices (is there a reason not to?)
         let choices = match inv.args.slash_command {
             true => quote::quote! { poise::slash_argument_choices!(#type_) },
             false => quote::quote! { vec![] },

src/choice_parameter.rs

@@ -0,0 +1,75 @@
+//! Contains the [`ChoiceParameter`] trait and the blanket [`crate::SlashArgument`] and
+//! [`crate::PopArgument`] impl
+
+use crate::serenity_prelude as serenity;
+
+/// This trait is implemented by [`crate::macros::ChoiceParameter`]. See its docs for more
+/// information
+pub trait ChoiceParameter: Sized {
+    /// Returns all possible choices for this parameter, in the order they will appear in Discord.
+    fn list() -> Vec<crate::CommandParameterChoice>;
+
+    /// Returns an instance of [`Self`] corresponding to the given index into [`Self::list()`]
+    fn from_index(index: usize) -> Option<Self>;
+
+    /// Parses the name as returned by [`Self::name()`] into an instance of [`Self`]
+    fn from_name(name: &str) -> Option<Self>;
+
+    /// Returns the non-localized name of this choice
+    fn name(&self) -> &'static str;
+
+    /// Returns the localized name for the given locale, if one is set
+    fn localized_name(&self, locale: &str) -> Option<&'static str>;
+}
+
+#[async_trait::async_trait]
+impl<T: ChoiceParameter> crate::SlashArgument for T {
+    async fn extract(
+        _: &serenity::Context,
+        _: crate::ApplicationCommandOrAutocompleteInteraction<'_>,
+        value: &serenity::json::Value,
+    ) -> ::std::result::Result<Self, crate::SlashArgError> {
+        let choice_key = value
+            .as_u64()
+            .ok_or(crate::SlashArgError::CommandStructureMismatch(
+                "expected u64",
+            ))?;
+
+        Self::from_index(choice_key as _).ok_or(crate::SlashArgError::CommandStructureMismatch(
+            "out of bounds choice key",
+        ))
+    }
+
+    fn create(builder: &mut serenity::CreateApplicationCommandOption) {
+        builder.kind(serenity::CommandOptionType::Integer);
+    }
+
+    fn choices() -> Vec<crate::CommandParameterChoice> {
+        Self::list()
+    }
+}
+
+#[async_trait::async_trait]
+impl<'a, T: ChoiceParameter> crate::PopArgument<'a> for T {
+    async fn pop_from(
+        args: &'a str,
+        attachment_index: usize,
+        ctx: &serenity::Context,
+        msg: &serenity::Message,
+    ) -> Result<(&'a str, usize, Self), (Box<dyn std::error::Error + Send + Sync>, Option<String>)>
+    {
+        let (args, attachment_index, s) =
+            crate::pop_prefix_argument!(String, args, attachment_index, ctx, msg).await?;
+
+        Ok((
+            args,
+            attachment_index,
+            Self::from_name(&s).ok_or((
+                Box::new(crate::InvalidChoice {
+                    __non_exhaustive: (),
+                }) as Box<dyn std::error::Error + Send + Sync>,
+                Some(s),
+            ))?,
+        ))
+    }
+}

src/lib.rs

@@ -384,6 +384,7 @@ Also, poise is a stat in Dark Souls
 */
 
 pub mod builtins;
+pub mod choice_parameter;
 pub mod cooldown;
 pub mod dispatch;
 pub mod event;
@@ -403,8 +404,8 @@ pub mod macros {
 
 #[doc(no_inline)]
 pub use {
-    cooldown::*, dispatch::*, event::*, framework::*, macros::*, modal::*, prefix_argument::*,
-    reply::*, slash_argument::*, structs::*, track_edits::*,
+    choice_parameter::*, cooldown::*, dispatch::*, event::*, framework::*, macros::*, modal::*,
+    prefix_argument::*, reply::*, slash_argument::*, structs::*, track_edits::*,
 };
 
 /// See [`builtins`]