Parse id arguments as their mentions where appropriate

src/prefix_argument/argument_trait.rs

@@ -2,7 +2,10 @@
 //! the auto-deref specialization emulation code to e.g. support more strings for bool parameters
 //! instead of the `FromStr` ones
 
-use super::{pop_string, InvalidBool, MissingAttachment, TooFewArguments};
+use super::{
+    pop_string, InvalidBool, InvalidChannelId, InvalidRoleId, InvalidUserId, MissingAttachment,
+    TooFewArguments,
+};
 use crate::serenity_prelude as serenity;
 use std::marker::PhantomData;
 
@@ -135,3 +138,84 @@ impl<'a> PopArgumentHack<'a, serenity::Attachment> for &PhantomData<serenity::At
         Ok((args, attachment_index + 1, attachment))
     }
 }
+
+#[async_trait::async_trait]
+impl<'a> PopArgumentHack<'a, serenity::UserId> for &PhantomData<serenity::UserId> {
+    async fn pop_from(
+        self,
+        args: &'a str,
+        attachment_index: usize,
+        ctx: &serenity::Context,
+        msg: &serenity::Message,
+    ) -> Result<
+        (&'a str, usize, serenity::UserId),
+        (Box<dyn std::error::Error + Send + Sync>, Option<String>),
+    > {
+        let (args, string) =
+            pop_string(args).map_err(|_| (TooFewArguments::default().into(), None))?;
+
+        if let Some(user_id) = string
+            .parse()
+            .ok()
+            .or_else(|| serenity::utils::parse_user_mention(&string))
+        {
+            Ok((args.trim_start(), attachment_index, user_id))
+        } else {
+            Err((InvalidUserId::default().into(), Some(string)))
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl<'a> PopArgumentHack<'a, serenity::RoleId> for &PhantomData<serenity::RoleId> {
+    async fn pop_from(
+        self,
+        args: &'a str,
+        attachment_index: usize,
+        ctx: &serenity::Context,
+        msg: &serenity::Message,
+    ) -> Result<
+        (&'a str, usize, serenity::RoleId),
+        (Box<dyn std::error::Error + Send + Sync>, Option<String>),
+    > {
+        let (args, string) =
+            pop_string(args).map_err(|_| (TooFewArguments::default().into(), None))?;
+
+        if let Some(user_id) = string
+            .parse()
+            .ok()
+            .or_else(|| serenity::utils::parse_role_mention(&string))
+        {
+            Ok((args.trim_start(), attachment_index, user_id))
+        } else {
+            Err((InvalidRoleId::default().into(), Some(string)))
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl<'a> PopArgumentHack<'a, serenity::ChannelId> for &PhantomData<serenity::ChannelId> {
+    async fn pop_from(
+        self,
+        args: &'a str,
+        attachment_index: usize,
+        ctx: &serenity::Context,
+        msg: &serenity::Message,
+    ) -> Result<
+        (&'a str, usize, serenity::ChannelId),
+        (Box<dyn std::error::Error + Send + Sync>, Option<String>),
+    > {
+        let (args, string) =
+            pop_string(args).map_err(|_| (TooFewArguments::default().into(), None))?;
+
+        if let Some(user_id) = string
+            .parse()
+            .ok()
+            .or_else(|| serenity::utils::parse_channel_mention(&string))
+        {
+            Ok((args.trim_start(), attachment_index, user_id))
+        } else {
+            Err((InvalidChannelId::default().into(), Some(string)))
+        }
+    }
+}

src/prefix_argument/mod.rs

@@ -125,6 +125,45 @@ impl std::fmt::Display for InvalidBool {
 }
 impl std::error::Error for InvalidBool {}
 
+/// Error thrown when the user enters a string that cannot be parsed as a UserId.
+#[derive(Default, Debug)]
+pub struct InvalidUserId {
+    #[doc(hidden)]
+    pub __non_exhaustive: (),
+}
+impl std::fmt::Display for InvalidUserId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("Enter a valid user's ID or a mention.")
+    }
+}
+impl std::error::Error for InvalidUserId {}
+
+/// Error thrown when the user enters a string that cannot be parsed as a RoleId.
+#[derive(Default, Debug)]
+pub struct InvalidRoleId {
+    #[doc(hidden)]
+    pub __non_exhaustive: (),
+}
+impl std::fmt::Display for InvalidRoleId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("Enter a valid role's ID or a mention.")
+    }
+}
+impl std::error::Error for InvalidRoleId {}
+
+/// Error thrown when the user enters a string that cannot be parsed as a RoleId.
+#[derive(Default, Debug)]
+pub struct InvalidChannelId {
+    #[doc(hidden)]
+    pub __non_exhaustive: (),
+}
+impl std::fmt::Display for InvalidChannelId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("Enter a valid channel's ID or a mention.")
+    }
+}
+impl std::error::Error for InvalidChannelId {}
+
 #[cfg(test)]
 #[test]
 fn test_pop_string() {