Make size, decode and encode derives work with non-suffixed literals

mls-rs-codec-derive/src/lib.rs

@@ -2,13 +2,17 @@
 // Copyright by contributors to this project.
 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+use std::str::FromStr;
+
 use darling::{
     ast::{self, Fields},
     FromDeriveInput, FromField, FromVariant,
 };
-use proc_macro2::TokenStream;
+use proc_macro2::{Literal, TokenStream};
 use quote::quote;
-use syn::{parse_macro_input, parse_quote, DeriveInput, Expr, Generics, Ident, Index, Path};
+use syn::{
+    parse_macro_input, parse_quote, Attribute, DeriveInput, Expr, Generics, Ident, Index, Lit, Path,
+};
 
 enum Operation {
     Size,
@@ -84,8 +88,9 @@ struct MlsVariantReceiver {
 }
 
 #[derive(FromDeriveInput)]
-#[darling(attributes(mls_codec))]
+#[darling(attributes(mls_codec), forward_attrs(repr))]
 struct MlsInputReceiver {
+    attrs: Vec<Attribute>,
     ident: Ident,
     generics: Generics,
     data: ast::Data<MlsVariantReceiver, MlsFieldReceiver>,
@@ -95,28 +100,86 @@ impl MlsInputReceiver {
     fn handle_input(&self, operation: Operation) -> TokenStream {
         match self.data {
             ast::Data::Struct(ref s) => struct_impl(s, operation),
-            ast::Data::Enum(ref e) => enum_impl(&self.ident, e, operation),
+            ast::Data::Enum(ref e) => enum_impl(&self.ident, &self.attrs, e, operation),
         }
     }
 }
 
-fn enum_impl(ident: &Ident, variants: &[MlsVariantReceiver], operation: Operation) -> TokenStream {
+fn repr_ident(attrs: &[Attribute]) -> Option<Ident> {
+    let repr_path = attrs
+        .iter()
+        .filter(|attr| matches!(attr.style, syn::AttrStyle::Outer))
+        .find(|attr| attr.path().is_ident("repr"))
+        .map(|repr| repr.parse_args())
+        .transpose()
+        .ok()
+        .flatten();
+
+    let Some(Expr::Path(path)) = repr_path else {
+        return None;
+    };
+
+    path.path
+        .segments
+        .iter()
+        .find(|s| s.ident != "C")
+        .map(|path| path.ident.clone())
+}
+
+/// Provides the discriminant for a given variant. If the variant does not specify a suffix
+/// and a `repr_ident` is provided, it will be appended to number.
+fn discriminant_for_variant(
+    variant: &MlsVariantReceiver,
+    repr_ident: &Option<Ident>,
+) -> TokenStream {
+    let discriminant = variant
+        .discriminant
+        .clone()
+        .expect("Enum discriminants must be explicitly defined");
+
+    let Expr::Lit(lit_expr) = &discriminant else {
+        return quote! {#discriminant};
+    };
+
+    let Lit::Int(lit_int) = &lit_expr.lit else {
+        return quote! {#discriminant};
+    };
+
+    if lit_int.suffix().is_empty() {
+        // This is dirty and there is probably a better way of doing this but I'm way too much of a noob at
+        // proc macros to pull it off...
+        // TODO: Add proper support for correctly ignoring transparent, packed and modifiers
+        let str = format!(
+            "{}{}",
+            lit_int.base10_digits(),
+            &repr_ident.clone().expect("Expected a repr(u*) to be provided or for the variant's discriminant to be defined with suffixed literals.")
+        );
+        Literal::from_str(&str)
+            .map(|l| quote! {#l})
+            .ok()
+            .unwrap_or_else(|| quote! {#discriminant})
+    } else {
+        quote! {#discriminant}
+    }
+}
+
+fn enum_impl(
+    ident: &Ident,
+    attrs: &[Attribute],
+    variants: &[MlsVariantReceiver],
+    operation: Operation,
+) -> TokenStream {
     let handle_error = operation.is_result().then_some(quote! { ? });
     let path = operation.path();
     let call = operation.call();
     let extras = operation.extras();
     let enum_name = &ident;
-
+    let repr_ident = repr_ident(attrs);
     if matches!(operation, Operation::Decode) {
         let cases = variants.iter().map(|variant| {
             let variant_name = &variant.ident;
 
-            // TODO: Calculate discriminant and support integers that are assumed types like u16,
-            // u32 etc based on repr()
-            let discriminant = &variant
-                .discriminant
-                .clone()
-                .expect("Enum discriminants must be explicitly defined");
+            let discriminant = discriminant_for_variant(variant, &repr_ident);
 
             // TODO: Support more than 1 field
             match variant.fields.len() {
@@ -142,10 +205,7 @@ fn enum_impl(ident: &Ident, variants: &[MlsVariantReceiver], operation: Operatio
     let cases = variants.iter().map(|variant| {
         let variant_name = &variant.ident;
 
-        let discriminant = &variant
-            .discriminant
-            .clone()
-            .expect("Enum discriminants must be explicitly defined");
+        let discriminant = discriminant_for_variant(variant, &repr_ident);
 
         let (parameter, field) = if variant.fields.is_empty() {
             (None, None)
@@ -220,6 +280,7 @@ where
     F: FnOnce(&MlsInputReceiver) -> TokenStream,
 {
     let input = parse_macro_input!(input as DeriveInput);
+
     let input = MlsInputReceiver::from_derive_input(&input).unwrap();
 
     let name = &input.ident;

mls-rs-codec/tests/macro_usage.rs

@@ -40,6 +40,14 @@ enum TestEnum {
     Case3(TestTupleStruct) = 42u16,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, MlsSize, MlsEncode, MlsDecode)]
+#[repr(u8)]
+enum TestEnumWithoutSuffixedLiterals {
+    Case1 = 1,
+    Case2(TestFieldStruct) = 200,
+    Case3(TestTupleStruct) = 42,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, MlsSize, MlsEncode, MlsDecode)]
 struct TestGeneric<T: MlsSize + MlsEncode + MlsDecode>(T);