Combine and sort common and custom fields using a Vec<Field>.

src/gen.rs

@@ -2,7 +2,12 @@
 
 use proc_macro2::{Span, TokenStream};
 use quote::{quote, ToTokens};
-use syn::{Attribute, Field, Ident};
+use syn::{
+    parse::{self, Parse, ParseStream},
+    parse_quote,
+    punctuated::Punctuated,
+    Attribute, Field, Ident, Token,
+};
 
 use crate::parse::{EventKind, RumaEventInput};
 
@@ -14,34 +19,99 @@ pub struct RumaEvent {
     /// The name of the type of the event's `content` field.
     content_name: Ident,
 
-    /// Additional named struct fields in the top level event struct.
-    fields: Option<Vec<Field>>,
+    /// Struct fields of the event.
+    fields: Vec<Field>,
 
     /// The kind of event.
+    #[allow(dead_code)]
     kind: EventKind,
 
     /// The name of the event.
     name: Ident,
 }
 
-impl RumaEvent {
-    /// Fills in the event's struct definition with fields common to all basic events.
-    fn common_basic_event_fields(&self) -> TokenStream {
+impl From<RumaEventInput> for RumaEvent {
+    fn from(input: RumaEventInput) -> Self {
+        let kind = input.kind;
+        let name = input.name;
+        let content_name = Ident::new(&format!("{}Content", &name), Span::call_site());
+
+        let mut fields = match kind {
+            EventKind::Event => {
+                populate_event_fields(content_name.clone(), input.fields.unwrap_or_else(Vec::new))
+            }
+            EventKind::RoomEvent => populate_room_event_fields(
+                content_name.clone(),
+                input.fields.unwrap_or_else(Vec::new),
+            ),
+            EventKind::StateEvent => {
+                populate_state_fields(content_name.clone(), input.fields.unwrap_or_else(Vec::new))
+            }
+        };
+
+        fields.sort_unstable_by_key(|field| field.ident.clone().unwrap());
+
+        Self {
+            attrs: input.attrs,
+            content_name,
+            fields,
+            kind,
+            name,
+        }
+    }
+}
+
+impl ToTokens for RumaEvent {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let attrs = &self.attrs;
         let content_name = &self.content_name;
 
-        quote! {
+        let event_fields = &self.fields;
+
+        let name = &self.name;
+
+        let content_docstring = format!("The payload for `{}`.", name);
+
+        let output = quote!(
+            #(#attrs),*
+            #[derive(Clone, Debug)]
+            pub struct #name {
+                #(#event_fields),*
+            }
+
+            #[doc = #content_docstring]
+            #[derive(Clone, Debug)]
+            pub struct #content_name {
+            }
+        );
+
+        output.to_tokens(tokens);
+    }
+}
+
+/// Fills in the event's struct definition with fields common to all basic events.
+fn populate_event_fields(content_name: Ident, mut fields: Vec<Field>) -> Vec<Field> {
+    let punctuated_fields: Punctuated<ParsableNamedField, Token![,]> = parse_quote! {
         /// The event's content.
         pub content: #content_name,
+    };
+
+    let mut additional_fields = Vec::with_capacity(punctuated_fields.len());
+
+    for punctuated_field in punctuated_fields {
+        additional_fields.push(punctuated_field.field);
     }
+
+    fields.extend(additional_fields);
+
+    fields
 }
 
 /// Fills in the event's struct definition with fields common to all room events.
-    fn common_room_event_fields(&self) -> TokenStream {
-        let common_basic_event_fields = self.common_basic_event_fields();
-
-        quote! {
-            #common_basic_event_fields
+fn populate_room_event_fields(content_name: Ident, fields: Vec<Field>) -> Vec<Field> {
+    let mut fields = populate_event_fields(content_name, fields);
 
+    let punctuated_fields: Punctuated<ParsableNamedField, Token![,]> = parse_quote! {
         /// The unique identifier for the event.
         pub event_id: ruma_identifiers::EventId,
 
@@ -57,72 +127,55 @@ impl RumaEvent {
 
         /// The unique identifier for the user who sent this event.
         pub sender: ruma_identifiers::UserId,
+    };
+
+    let mut additional_fields = Vec::with_capacity(punctuated_fields.len());
+
+    for punctuated_field in punctuated_fields {
+        additional_fields.push(punctuated_field.field);
     }
+
+    fields.extend(additional_fields);
+
+    fields
 }
 
 /// Fills in the event's struct definition with fields common to all state events.
-    fn common_state_event_fields(&self) -> TokenStream {
-        let content_name = &self.content_name;
-        let common_room_event_fields = self.common_room_event_fields();
-
-        quote! {
-            #common_room_event_fields
+fn populate_state_fields(content_name: Ident, fields: Vec<Field>) -> Vec<Field> {
+    let mut fields = populate_room_event_fields(content_name.clone(), fields);
 
+    let punctuated_fields: Punctuated<ParsableNamedField, Token![,]> = parse_quote! {
         /// The previous content for this state key, if any.
         pub prev_content: Option<#content_name>,
 
         /// A key that determines which piece of room state the event represents.
         pub state_key: String,
-        }
-    }
-}
-
-impl From<RumaEventInput> for RumaEvent {
-    fn from(input: RumaEventInput) -> Self {
-        Self {
-            attrs: input.attrs,
-            content_name: Ident::new(&format!("{}Content", input.name), Span::call_site()),
-            fields: input.fields,
-            kind: input.kind,
-            name: input.name,
-        }
-    }
-}
-
-impl ToTokens for RumaEvent {
-    fn to_tokens(&self, tokens: &mut TokenStream) {
-        let attrs = &self.attrs;
-        let content_name = &self.content_name;
-
-        let common_event_fields = match self.kind {
-            EventKind::Event => self.common_basic_event_fields(),
-            EventKind::RoomEvent => self.common_room_event_fields(),
-            EventKind::StateEvent => self.common_state_event_fields(),
     };
 
-        let event_fields = match &self.fields {
-            Some(fields) => fields.clone(),
-            None => vec![],
-        };
+    let mut additional_fields = Vec::with_capacity(punctuated_fields.len());
 
-        let name = &self.name;
-
-        let content_docstring = format!("The payload for `{}`.", name);
-
-        let output = quote!(
-            #(#attrs),*
-            #[derive(Clone, Debug)]
-            pub struct #name {
-                #common_event_fields
-                #(#event_fields),*
+    for punctuated_field in punctuated_fields {
+        additional_fields.push(punctuated_field.field);
     }
 
-            #[doc = #content_docstring]
-            #[derive(Clone, Debug)]
-            pub struct #content_name {
-            }
-        );
+    fields.extend(additional_fields);
 
-        output.to_tokens(tokens);
+    fields
+}
+
+/// A wrapper around `syn::Field` that makes it possible to parse `Punctuated<Field, Token![,]>`
+/// from a `TokenStream`.
+///
+/// See https://github.com/dtolnay/syn/issues/651 for more context.
+struct ParsableNamedField {
+    /// The wrapped `Field`.
+    pub field: Field,
+}
+
+impl Parse for ParsableNamedField {
+    fn parse(input: ParseStream<'_>) -> parse::Result<Self> {
+        let field = Field::parse_named(input)?;
+
+        Ok(Self { field })
     }
 }