events: Refactor EventContent derive code

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

@@ -103,12 +103,6 @@ pub fn expand_event_content(
     input: &DeriveInput,
     ruma_events: &TokenStream,
 ) -> syn::Result<TokenStream> {
-    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };
-    let serde = quote! { #ruma_events::exports::serde };
-    let serde_json = quote! { #ruma_events::exports::serde_json };
-
-    let ident = &input.ident;
-
     let content_attr = input
         .attrs
         .iter()
@@ -150,10 +144,37 @@ pub fn expand_event_content(
     };
 
     // We only generate redacted content structs for state and message events
-    let redacted = if needs_redacted(&content_attr, event_kind) {
+    let redacted_event_content = needs_redacted(&content_attr, event_kind)
+        .then(|| generate_redacted_event_content(input, event_type, ruma_events, event_kind))
+        .transpose()?;
+
+    let event_content_impl = generate_event_content_impl(&input.ident, 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
+        #marker_trait_impl
+    })
+}
+
+fn generate_redacted_event_content(
+    input: &DeriveInput,
+    event_type: &LitStr,
+    ruma_events: &TokenStream,
+    event_kind: Option<&EventKind>,
+) -> Result<TokenStream, syn::Error> {
+    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };
+    let serde = quote! { #ruma_events::exports::serde };
+    let serde_json = quote! { #ruma_events::exports::serde_json };
+
+    let ident = &input.ident;
     let doc = format!("The payload for a redacted `{}`", ident);
     let redacted_ident = format_ident!("Redacted{}", ident);
-        let kept_redacted_fields = if let syn::Data::Struct(syn::DataStruct {
+
+    let kept_redacted_fields =
+        if let syn::Data::Struct(syn::DataStruct {
             fields: syn::Fields::Named(syn::FieldsNamed { named, .. }),
             ..
         }) = &input.data
@@ -191,12 +212,9 @@ pub fn expand_event_content(
         } else {
             vec![]
         };
+
     let redaction_struct_fields = kept_redacted_fields.iter().flat_map(|f| &f.ident);
 
-        // redacted_fields allows one to declare an empty redacted event without braces,
-        // otherwise `RedactedWhateverEventContent {}` is needed.
-        // The redacted_return is used in `EventContent::redacted` which only returns
-        // zero sized types (unit structs).
     let (redacted_fields, redacted_return) = if kept_redacted_fields.is_empty() {
         (quote! { ; }, quote! { Ok(#redacted_ident {}) })
     } else {
@@ -212,19 +230,13 @@ pub fn expand_event_content(
         )
     };
 
-        let has_deserialize_fields = if kept_redacted_fields.is_empty() {
+    let (has_deserialize_fields, has_serialize_fields) = if kept_redacted_fields.is_empty() {
-            quote! { #ruma_events::HasDeserializeFields::False }
+        (quote! { #ruma_events::HasDeserializeFields::False }, quote! { false })
     } else {
-            quote! { #ruma_events::HasDeserializeFields::True }
+        (quote! { #ruma_events::HasDeserializeFields::True }, quote! { true })
     };
 
-        let has_serialize_fields = if kept_redacted_fields.is_empty() {
+    let constructor = kept_redacted_fields.is_empty().then(|| {
-            quote! { false }
-        } else {
-            quote! { true }
-        };
-
-        let initializer = if kept_redacted_fields.is_empty() {
         let doc = format!("Creates an empty {}.", redacted_ident);
         quote! {
             impl #redacted_ident {
@@ -234,9 +246,7 @@ pub fn expand_event_content(
                 }
             }
         }
-        } else {
+    });
-            TokenStream::new()
-        };
 
     let redacted_event_content =
         generate_event_content_impl(&redacted_ident, event_type, ruma_events);
@@ -253,7 +263,7 @@ pub fn expand_event_content(
         _ => TokenStream::new(),
     };
 
-        quote! {
+    Ok(quote! {
         // this is the non redacted event content's impl
         #[automatically_derived]
         impl #ruma_events::RedactContent for #ident {
@@ -271,7 +281,7 @@ pub fn expand_event_content(
         #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
         pub struct #redacted_ident #redacted_fields
 
-            #initializer
+        #constructor
 
         #redacted_event_content
 
@@ -297,24 +307,10 @@ pub fn expand_event_content(
         }
 
         #redacted_event_content_derive
-        }
-    } else {
-        TokenStream::new()
-    };
-
-    let event_content_derive =
-        event_kind.map(|k| generate_event_content_derive(k, ident, ruma_events)).transpose()?;
-
-    let event_content = generate_event_content_impl(ident, event_type, ruma_events);
-
-    Ok(quote! {
-        #event_content
-        #event_content_derive
-        #redacted
     })
 }
 
-fn generate_event_content_derive(
+fn generate_marker_trait_impl(
     event_kind: &EventKind,
     ident: &Ident,
     ruma_events: &TokenStream,