Fix deserialization of Guild::application_id

Fix the deserialization of the `Guild::application_id` structfield.
Additionally, create a new ID type for it.

A test has been added for this.

src/model/guild/mod.rs

@@ -49,7 +49,7 @@ pub struct Guild {
     /// channel before being moved to an AFK channel -- if one exists.
     pub afk_timeout: u64,
     /// Application ID of the guild creator if it is bot-created.
-    pub application_id: Option<u64>,
+    pub application_id: Option<ApplicationId>,
     /// All voice and text channels contained within a guild.
     ///
     /// This contains all channels regardless of permissions (i.e. the ability
@@ -1427,7 +1427,7 @@ impl<'de> Deserialize<'de> for Guild {
             .and_then(u64::deserialize)
             .map_err(DeError::custom)?;
         let application_id = match map.remove("application_id") {
-            Some(v) => serde_json::from_value::<Option<u64>>(v)
+            Some(v) => serde_json::from_value::<Option<ApplicationId>>(v)
                 .map_err(DeError::custom)?,
             None => None,
         };

src/model/mod.rs

@@ -105,6 +105,8 @@ macro_rules! id_u64 {
 }
 
 id_u64! {
+    /// An identifier for an Application.
+    ApplicationId;
     /// An identifier for a Channel
     ChannelId;
     /// An identifier for an Emoji

tests/resources/guild_some_application_id.json

@@ -0,0 +1 @@
+{"afk_channel_id":null,"afk_timeout":300,"application_id":"245571012924538880","channels":[{"guild_id":334866293213888514,"id":"334866293213888514","last_message_id":"334866823763722242","name":"general","permission_overwrites":[],"position":0,"topic":null,"type":0},{"bitrate":64000,"guild_id":334866293213888514,"id":"334866293213888515","name":"General","permission_overwrites":[],"position":0,"type":2,"user_limit":0}],"default_message_notifications":0,"emojis":[],"explicit_content_filter":0,"features":[],"icon":null,"id":"334866293213888514","joined_at":"2017-07-13T01:19:05.876000+00:00","large":false,"member_count":1,"members":[{"deaf":false,"guild_id":334866293213888514,"joined_at":"2017-07-13T01:19:05.876000+00:00","mute":false,"roles":[],"user":{"avatar":"96fd89e899fbb203b9851df3e7dcbf5d","bot":true,"discriminator":"9653","id":"245571012924538880","username":"nano"}}],"mfa_level":0,"name":"helo","owner_id":"245571012924538880","presences":[{"game":{"name":"nano help [1/1]","type":0},"status":"online","user":{"id":"245571012924538880"}}],"region":"eu-central","roles":[{"color":0,"hoist":false,"id":"334866293213888514","managed":false,"mentionable":false,"name":"@everyone","permissions":104324161,"position":0}],"splash":null,"system_channel_id":null,"verification_level":0,"voice_states":[]}

tests/test_deser.rs

@@ -58,6 +58,12 @@ fn guild_channel_1_rest() {
     p!(GuildChannel, "guild_channel_rest_1");
 }
 
+// A guild that has some application ID.
+#[test]
+fn guild_some_application_id() {
+    p!(Guild, "guild_some_application_id");
+}
+
 // A Discord API GUILD_CREATE.
 #[test]
 fn guild_create() {