events: Generate From impls for event (content) enums

crates/ruma-events-macros/src/event_enum.rs

@@ -2,7 +2,7 @@
 
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote, ToTokens};
-use syn::{Attribute, Ident, LitStr};
+use syn::{Attribute, Data, DataEnum, DeriveInput, Ident, LitStr};
 
 use crate::event_parse::{EventEnumDecl, EventEnumEntry, EventKind, EventKindVariation};
 
@@ -186,6 +186,8 @@ fn expand_any_with_deser(
 
     let redact_impl = expand_redact(&ident, kind, var, variants, ruma_events);
 
+    let from_impl = expand_from_impl(ident, &content, variants);
+
     Some(quote! {
         #any_enum
 
@@ -198,9 +200,34 @@ fn expand_any_with_deser(
         #event_deserialize_impl
 
         #redacted_enum
+
+        #from_impl
     })
 }
 
+fn expand_from_impl(
+    ty: Ident,
+    content: &[TokenStream],
+    variants: &[EventEnumVariant],
+) -> TokenStream {
+    let from_impls = content.iter().zip(variants).map(|(content, variant)| {
+        let ident = &variant.ident;
+        let attrs = &variant.attrs;
+
+        quote! {
+            #[automatically_derived]
+            #(#attrs)*
+            impl From<#content> for #ty {
+                fn from(c: #content) -> Self {
+                    Self::#ident(c)
+                }
+            }
+        }
+    });
+
+    quote! { #( #from_impls )* }
+}
+
 fn expand_conversion_impl(
     kind: &EventKind,
     var: &EventKindVariation,
@@ -489,11 +516,14 @@ fn expand_content_enum(
         }
     });
 
+    let from_impl = expand_from_impl(ident, &content, variants);
+
     quote! {
         #content_enum
         #event_content_impl
         #marker_trait_impl
         #redacted_content_enum
+        #from_impl
     }
 }
 
@@ -1037,3 +1067,32 @@ impl EventEnumEntry {
         Ok(EventEnumVariant { attrs, ident })
     }
 }
+
+pub(crate) fn expand_from_impls_derived(input: DeriveInput) -> TokenStream {
+    let variants = match &input.data {
+        Data::Enum(DataEnum { variants, .. }) => variants,
+        _ => panic!("this derive macro only works with enums"),
+    };
+
+    let from_impls = variants.iter().map(|variant| match &variant.fields {
+        syn::Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
+            let inner_struct = &fields.unnamed.first().unwrap().ty;
+            let var_ident = &variant.ident;
+            let id = &input.ident;
+            quote! {
+                impl From<#inner_struct> for #id {
+                    fn from(c: #inner_struct) -> Self {
+                        Self::#var_ident(c)
+                    }
+                }
+            }
+        }
+        _ => {
+            panic!("this derive macro only works with enum variants with a single unnamed field")
+        }
+    });
+
+    quote! {
+        #( #from_impls )*
+    }
+}

crates/ruma-events-macros/src/lib.rs

@@ -15,6 +15,8 @@ use proc_macro_crate::{crate_name, FoundCrate};
 use quote::{format_ident, quote};
 use syn::{parse_macro_input, DeriveInput};
 
+use crate::event_enum::expand_from_impls_derived;
+
 use self::{
     event::expand_event, event_content::expand_event_content, event_enum::expand_event_enum,
     event_type::expand_event_type_enum,
@@ -107,3 +109,10 @@ pub(crate) fn import_ruma_events() -> pm2::TokenStream {
         quote! { ::ruma_events }
     }
 }
+
+/// Generates `From` implementations for event enums.
+#[proc_macro_derive(EventEnumFromEvent)]
+pub fn derive_from_event_to_enum(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    expand_from_impls_derived(input).into()
+}

crates/ruma-events/CHANGELOG.md

@@ -1,5 +1,9 @@
 # [unreleased]
 
+Improvements:
+
+* Add `From` implementations for event and event content enums
+
 # 0.24.4
 
 Improvements:

crates/ruma-events/src/enums.rs

@@ -1,5 +1,5 @@
 use ruma_common::MilliSecondsSinceUnixEpoch;
-use ruma_events_macros::event_enum;
+use ruma_events_macros::{event_enum, EventEnumFromEvent};
 use ruma_identifiers::{EventId, RoomId, RoomVersionId, UserId};
 use serde::{de, Deserialize, Serialize};
 use serde_json::value::RawValue as RawJsonValue;
@@ -146,7 +146,7 @@ macro_rules! room_ev_accessor {
 
 /// Any room event.
 #[allow(clippy::large_enum_variant, clippy::exhaustive_enums)]
-#[derive(Clone, Debug, Serialize)]
+#[derive(Clone, Debug, Serialize, EventEnumFromEvent)]
 #[serde(untagged)]
 pub enum AnyRoomEvent {
     /// Any message event.
@@ -171,7 +171,7 @@ impl AnyRoomEvent {
 
 /// Any sync room event (room event without a `room_id`, as returned in `/sync` responses)
 #[allow(clippy::large_enum_variant, clippy::exhaustive_enums)]
-#[derive(Clone, Debug, Serialize)]
+#[derive(Clone, Debug, Serialize, EventEnumFromEvent)]
 #[serde(untagged)]
 pub enum AnySyncRoomEvent {
     /// Any sync message event
@@ -264,7 +264,7 @@ impl<'de> Deserialize<'de> for AnySyncRoomEvent {
 
 /// Any redacted room event.
 #[allow(clippy::large_enum_variant, clippy::exhaustive_enums)]
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, EventEnumFromEvent)]
 pub enum AnyRedactedRoomEvent {
     /// Any message event that has been redacted.
     Message(AnyRedactedMessageEvent),
@@ -300,7 +300,7 @@ impl From<AnyRedactedRoomEvent> for AnyRoomEvent {
 
 /// Any redacted sync room event (room event without a `room_id`, as returned in `/sync` responses)
 #[allow(clippy::large_enum_variant, clippy::exhaustive_enums)]
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, EventEnumFromEvent)]
 pub enum AnyRedactedSyncRoomEvent {
     /// Any sync message event that has been redacted.
     Message(AnyRedactedSyncMessageEvent),