From 3f370c5f1be5d50279c1042bfa7319e341daf2b9 Mon Sep 17 00:00:00 2001
From: Devin Ragotzy <devin.ragotzy@gmail.com>
Date: Sat, 1 Aug 2020 15:56:33 -0400
Subject: [PATCH] Add PartialEq/Eq and PartialOrd/Ord to the event structs with
 event_ids

---
 ruma-events-macros/src/event.rs | 35 +++++++++++++++++++++++++++++++++
 ruma-events/src/event_kinds.rs  |  4 ++++
 2 files changed, 39 insertions(+)

diff --git a/ruma-events-macros/src/event.rs b/ruma-events-macros/src/event.rs
index 1e314a5e..22fe6b41 100644
--- a/ruma-events-macros/src/event.rs
+++ b/ruma-events-macros/src/event.rs
@@ -42,12 +42,16 @@ pub fn expand_event(input: DeriveInput) -> syn::Result<TokenStream> {
 
     let conversion_impl = expand_from_into(&input, &kind, &var, &fields);
 
+    let eq_impl = expand_eq_ord_event(&input, &fields);
+
     Ok(quote! {
         #conversion_impl
 
         #serialize_impl
 
         #deserialize_impl
+
+        #eq_impl
     })
 }
 
@@ -371,6 +375,37 @@ fn expand_from_into(
     }
 }
 
+fn expand_eq_ord_event(input: &DeriveInput, fields: &[Field]) -> Option<TokenStream> {
+    if fields.iter().flat_map(|f| f.ident.as_ref()).any(|f| f == "event_id") {
+        let ident = &input.ident;
+        let (impl_gen, ty_gen, where_clause) = input.generics.split_for_impl();
+
+        Some(quote! {
+            impl #impl_gen ::std::cmp::PartialEq for #ident #ty_gen #where_clause {
+                fn eq(&self, other: &Self) -> bool {
+                    self.event_id == other.event_id
+                }
+            }
+
+            impl #impl_gen ::std::cmp::Eq for #ident #ty_gen #where_clause {}
+
+            impl #impl_gen ::std::cmp::PartialOrd for #ident #ty_gen #where_clause {
+                fn partial_cmp(&self, other: &Self) -> ::std::option::Option<::std::cmp::Ordering> {
+                    self.event_id.partial_cmp(&other.event_id)
+                }
+            }
+
+            impl #impl_gen ::std::cmp::Ord for #ident #ty_gen #where_clause {
+                fn cmp(&self, other: &Self) -> ::std::cmp::Ordering {
+                    self.event_id.cmp(&other.event_id)
+                }
+            }
+        })
+    } else {
+        None
+    }
+}
+
 /// CamelCase's a field ident like "foo_bar" to "FooBar".
 fn to_camel_case(name: &Ident) -> Ident {
     let span = name.span();
diff --git a/ruma-events/src/event_kinds.rs b/ruma-events/src/event_kinds.rs
index 94949f85..919c73d2 100644
--- a/ruma-events/src/event_kinds.rs
+++ b/ruma-events/src/event_kinds.rs
@@ -34,6 +34,10 @@ pub struct SyncEphemeralRoomEvent<C: EphemeralRoomEventContent> {
 }
 
 /// Message event.
+///
+/// `MessageEvent` implements the comparison trait's using only
+/// the `event_id` field, a sorted list would be sorted lexicographically based on
+/// the event's `EventId`.
 #[derive(Clone, Debug, Event)]
 pub struct MessageEvent<C: MessageEventContent> {
     /// Data specific to the event type.