From 9445e8756afab050addd487443dcca2e262ce9a7 Mon Sep 17 00:00:00 2001
From: Jonas Platte <jplatte+git@posteo.de>
Date: Wed, 11 Aug 2021 20:30:17 +0200
Subject: [PATCH] events: Derive / implement StaticEventContent for all
 relevant types

---
 .../ruma-events-macros/src/event_content.rs   | 40 ++++++++++++++++++-
 crates/ruma-events/CHANGELOG.md               |  5 +++
 crates/ruma-events/src/lib.rs                 |  3 ++
 crates/ruma-events/src/presence.rs            |  7 ++++
 4 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/crates/ruma-events-macros/src/event_content.rs b/crates/ruma-events-macros/src/event_content.rs
index 57214003..6bf9d680 100644
--- a/crates/ruma-events-macros/src/event_content.rs
+++ b/crates/ruma-events-macros/src/event_content.rs
@@ -149,12 +149,16 @@ pub fn expand_event_content(
         .transpose()?;
 
     let event_content_impl = generate_event_content_impl(&input.ident, event_type, ruma_events);
+    let static_event_content_impl = event_kind.map(|k| {
+        generate_static_event_content_impl(&input.ident, k, false, event_type, ruma_events)
+    });
     let marker_trait_impl =
         event_kind.map(|k| generate_marker_trait_impl(k, &input.ident, ruma_events)).transpose()?;
 
     Ok(quote! {
         #redacted_event_content
         #event_content_impl
+        #static_event_content_impl
         #marker_trait_impl
     })
 }
@@ -251,7 +255,7 @@ fn generate_redacted_event_content(
     let redacted_event_content =
         generate_event_content_impl(&redacted_ident, event_type, ruma_events);
 
-    let redacted_event_content_derive = match event_kind {
+    let marker_trait_impl = match event_kind {
         Some(EventKind::Message) => quote! {
             #[automatically_derived]
             impl #ruma_events::RedactedMessageEventContent for #redacted_ident {}
@@ -263,6 +267,10 @@ fn generate_redacted_event_content(
         _ => TokenStream::new(),
     };
 
+    let static_event_content_impl = event_kind.map(|k| {
+        generate_static_event_content_impl(&redacted_ident, k, true, event_type, ruma_events)
+    });
+
     Ok(quote! {
         // this is the non redacted event content's impl
         #[automatically_derived]
@@ -306,7 +314,8 @@ fn generate_redacted_event_content(
             }
         }
 
-        #redacted_event_content_derive
+        #static_event_content_impl
+        #marker_trait_impl
     })
 }
 
@@ -368,6 +377,33 @@ fn generate_event_content_impl(
     }
 }
 
+fn generate_static_event_content_impl(
+    ident: &Ident,
+    event_kind: &EventKind,
+    redacted: bool,
+    event_type: &LitStr,
+    ruma_events: &TokenStream,
+) -> TokenStream {
+    let event_kind = match event_kind {
+        EventKind::GlobalAccountData => quote! { GlobalAccountData },
+        EventKind::RoomAccountData => quote! { RoomAccountData },
+        EventKind::Ephemeral => quote! { EphemeralRoomData },
+        EventKind::Message => quote! { Message { redacted: #redacted } },
+        EventKind::State => quote! { State { redacted: #redacted } },
+        EventKind::ToDevice => quote! { ToDevice },
+        EventKind::Redaction | EventKind::Presence | EventKind::Decrypted => {
+            unreachable!("not a valid event content kind")
+        }
+    };
+
+    quote! {
+        impl #ruma_events::StaticEventContent for #ident {
+            const KIND: #ruma_events::EventKind = #ruma_events::EventKind::#event_kind;
+            const TYPE: &'static ::std::primitive::str = #event_type;
+        }
+    }
+}
+
 fn needs_redacted(input: &[MetaAttrs], event_kind: Option<&EventKind>) -> bool {
     // `is_custom` means that the content struct does not need a generated
     // redacted struct also. If no `custom_redacted` attrs are found the content
diff --git a/crates/ruma-events/CHANGELOG.md b/crates/ruma-events/CHANGELOG.md
index c6d8cb7a..a39358c1 100644
--- a/crates/ruma-events/CHANGELOG.md
+++ b/crates/ruma-events/CHANGELOG.md
@@ -14,6 +14,11 @@ Breaking changes:
   * It doesn't have the `relates_to` field `EncryptedEventContent` has
 * Upgrade dependencies
 
+Improvements:
+
+* Add the `StaticEventContent` trait for abstracting over event content struct
+  types (with a type known at compile-time)
+
 # 0.24.0
 
 Yanked, was released too early missing another important breaking change.
diff --git a/crates/ruma-events/src/lib.rs b/crates/ruma-events/src/lib.rs
index 1e361f40..5f81e9bd 100644
--- a/crates/ruma-events/src/lib.rs
+++ b/crates/ruma-events/src/lib.rs
@@ -407,6 +407,9 @@ pub enum EventKind {
 
     /// To-device event kind.
     ToDevice,
+
+    /// Presence event kind.
+    Presence,
 }
 
 /// `HasDeserializeFields` is used in the code generated by the `Event` derive
diff --git a/crates/ruma-events/src/presence.rs b/crates/ruma-events/src/presence.rs
index b278bf45..85014529 100644
--- a/crates/ruma-events/src/presence.rs
+++ b/crates/ruma-events/src/presence.rs
@@ -8,6 +8,8 @@ use ruma_events_macros::{Event, EventContent};
 use ruma_identifiers::{MxcUri, UserId};
 use serde::{Deserialize, Serialize};
 
+use crate::{EventKind, StaticEventContent};
+
 /// Presence event.
 #[derive(Clone, Debug, Event)]
 #[allow(clippy::exhaustive_structs)]
@@ -71,6 +73,11 @@ impl PresenceEventContent {
     }
 }
 
+impl StaticEventContent for PresenceEventContent {
+    const KIND: EventKind = EventKind::Presence;
+    const TYPE: &'static str = "m.presence";
+}
+
 #[cfg(test)]
 mod tests {
     use js_int::uint;