Add rename support for derived atom names

dannote · dannote · commit b630cb31f2fc · 2026-05-27T15:03:26.000+03:00
diff --git a/rustler_codegen/src/context.rs b/rustler_codegen/src/context.rs
@@ -1,7 +1,7 @@
 use heck::ToSnakeCase;
 use proc_macro2::{Span, TokenStream};
 use quote::quote;
-use syn::{Data, Field, Fields, Ident, Lifetime, Lit, Meta, TypeParam, Variant};
+use syn::{Attribute, Data, Field, Fields, Ident, Lifetime, Lit, Meta, TypeParam, Variant};
 
 use super::RustlerAttr;
 
@@ -110,29 +110,49 @@ impl<'a> Context<'a> {
                 .iter()
                 .map(|field| {
                     let atom_fun = Self::field_to_atom_fun(field);
-
-                    let ident = field.ident.as_ref().unwrap();
-                    let ident_str = ident.to_string();
-                    let ident_str = Self::remove_raw(&ident_str);
+                    let atom_name = Self::field_atom_name(field);
 
                     quote! {
-                        #atom_fun = #ident_str,
+                        #atom_fun = #atom_name,
                     }
                 })
                 .collect()
         })
     }
 
     pub fn field_to_atom_fun(field: &Field) -> Ident {
-        let ident = field.ident.as_ref().unwrap();
-        Self::ident_to_atom_fun(ident)
+        Self::atom_fun(&Self::field_atom_name(field))
+    }
+
+    pub fn field_atom_name(field: &Field) -> String {
+        Self::rename_attr(&field.attrs).unwrap_or_else(|| {
+            let ident = field.ident.as_ref().unwrap();
+            Self::ident_to_atom_name(ident)
+        })
+    }
+
+    pub fn variant_to_atom_fun(variant: &Variant) -> Ident {
+        Self::atom_fun(&Self::variant_atom_name(variant))
     }
 
-    pub fn ident_to_atom_fun(ident: &Ident) -> Ident {
-        let ident_str = ident.to_string().to_snake_case();
-        let ident_str = Self::remove_raw(&ident_str);
+    pub fn variant_atom_name(variant: &Variant) -> String {
+        Self::rename_attr(&variant.attrs)
+            .unwrap_or_else(|| Self::ident_to_atom_name(&variant.ident))
+    }
+
+    pub fn ident_to_atom_name(ident: &Ident) -> String {
+        let ident_str = ident.to_string();
+        Self::remove_raw(&ident_str).to_snake_case()
+    }
+
+    fn atom_fun(atom_name: &str) -> Ident {
+        let suffix = atom_name
+            .as_bytes()
+            .iter()
+            .map(|byte| format!("{byte:02x}"))
+            .collect::<String>();
 
-        Ident::new(&format!("atom_{ident_str}"), Span::call_site())
+        Ident::new(&format!("atom_{}", suffix), Span::call_site())
     }
 
     pub fn escape_ident_with_index(ident_str: &str, index: usize, infix: &str) -> Ident {
@@ -161,6 +181,33 @@ impl<'a> Context<'a> {
             .expect("split has always at least one element")
     }
 
+    fn rename_attr(attrs: &[Attribute]) -> Option<String> {
+        attrs.iter().find_map(|attr| {
+            if !attr.path().is_ident("rustler") {
+                return None;
+            }
+
+            let Meta::List(list) = &attr.meta else {
+                return None;
+            };
+
+            let mut rename = None;
+            list.parse_nested_meta(|nested_meta| {
+                if nested_meta.path.is_ident("rename") {
+                    let value = nested_meta.value()?;
+                    let lit: syn::LitStr = value.parse()?;
+                    rename = Some(lit.value());
+                    Ok(())
+                } else {
+                    Err(nested_meta.error("Expected rename in rustler attribute"))
+                }
+            })
+            .unwrap_or_else(|err| panic!("{}", err));
+
+            rename
+        })
+    }
+
     fn encode_decode_attr_set(attrs: &[RustlerAttr]) -> bool {
         attrs
             .iter()
diff --git a/rustler_codegen/src/tagged_enum.rs b/rustler_codegen/src/tagged_enum.rs
@@ -1,7 +1,6 @@
 use proc_macro2::{Span, TokenStream};
 use quote::{quote, quote_spanned};
 
-use heck::ToSnakeCase;
 use std::collections::HashMap;
 use syn::{self, spanned::Spanned, Field, Fields, FieldsNamed, FieldsUnnamed, Ident, Variant};
 
@@ -18,28 +17,25 @@ pub fn transcoder_decorator(ast: &syn::DeriveInput) -> TokenStream {
     let atoms = variants
         .iter()
         .flat_map(|variant| {
-            let mut ret = if let Fields::Named(fields) = &variant.fields {
+            let fields = if let Fields::Named(fields) = &variant.fields {
                 fields
                     .named
                     .iter()
                     .map(|field| {
-                        field
-                            .ident
-                            .as_ref()
-                            .expect("Named fields must have an ident.")
+                        (
+                            Context::field_atom_name(field),
+                            Context::field_to_atom_fun(field),
+                        )
                     })
                     .collect::<Vec<_>>()
             } else {
                 vec![]
             };
 
-            ret.push(&variant.ident);
-            ret
-        })
-        .map(|atom_ident| {
-            let atom_str = atom_ident.to_string().to_snake_case();
-            let atom_fn = Context::ident_to_atom_fun(atom_ident);
-            (atom_str, atom_fn)
+            fields.into_iter().chain(std::iter::once((
+                Context::variant_atom_name(variant),
+                Context::variant_to_atom_fun(variant),
+            )))
         })
         .collect::<HashMap<_, _>>()
         .into_iter()
@@ -89,7 +85,7 @@ fn gen_decoder(ctx: &Context, variants: &[&Variant], atoms_module_name: &Ident)
         .iter()
         .filter_map(|variant| {
             let variant_ident = &variant.ident;
-            let atom_fn = Context::ident_to_atom_fun(variant_ident);
+            let atom_fn = Context::variant_to_atom_fun(variant);
             match &variant.fields {
                 Fields::Unit => Some(gen_unit_decoder(enum_name, variant_ident, atom_fn)),
                 _ => None,
@@ -100,7 +96,7 @@ fn gen_decoder(ctx: &Context, variants: &[&Variant], atoms_module_name: &Ident)
         .iter()
         .filter_map(|variant| {
             let variant_ident = &variant.ident;
-            let atom_fn = Context::ident_to_atom_fun(variant_ident);
+            let atom_fn = Context::variant_to_atom_fun(variant);
             match &variant.fields {
                 Fields::Unnamed(fields) => Some(gen_unnamed_decoder(
                     enum_name,
@@ -161,7 +157,7 @@ fn gen_encoder(ctx: &Context, variants: &[&Variant], atoms_module_name: &Ident)
         .iter()
         .map(|variant| {
             let variant_ident = &variant.ident;
-            let atom_fn = Context::ident_to_atom_fun(variant_ident);
+            let atom_fn = Context::variant_to_atom_fun(variant);
 
             match &variant.fields {
                 Fields::Unit => gen_unit_encoder(enum_name, variant_ident, atom_fn),
diff --git a/rustler_codegen/tests/ui/derive-rename-invalid.rs b/rustler_codegen/tests/ui/derive-rename-invalid.rs
@@ -0,0 +1,9 @@
+use rustler_codegen::NifMap;
+
+#[derive(NifMap)]
+struct InvalidRename {
+    #[rustler(rename)]
+    value: i32,
+}
+
+fn main() {}
diff --git a/rustler_codegen/tests/ui/derive-rename-invalid.stderr b/rustler_codegen/tests/ui/derive-rename-invalid.stderr
@@ -0,0 +1,7 @@
+error: proc-macro derive panicked
+ --> tests/ui/derive-rename-invalid.rs:3:10
+  |
+3 | #[derive(NifMap)]
+  |          ^^^^^^
+  |
+  = help: message: expected `=`
diff --git a/rustler_tests/lib/rustler_test.ex b/rustler_tests/lib/rustler_test.ex
@@ -110,13 +110,16 @@ defmodule RustlerTest do
   def tuple_echo(_), do: err()
   def record_echo(_), do: err()
   def map_echo(_), do: err()
+  def renamed_map_echo(_), do: err()
+  def unicode_renamed_map_echo(_), do: err()
   def exception_echo(_), do: err()
   def struct_echo(_), do: err()
   def unit_enum_echo(_), do: err()
   def tagged_enum_1_echo(_), do: err()
   def tagged_enum_2_echo(_), do: err()
   def tagged_enum_3_echo(_), do: err()
   def tagged_enum_4_echo(_), do: err()
+  def renamed_tagged_enum_echo(_), do: err()
   def untagged_enum_echo(_), do: err()
   def untagged_enum_with_truthy(_), do: err()
   def untagged_enum_for_issue_370(_), do: err()
diff --git a/rustler_tests/native/rustler_test/src/test_codegen.rs b/rustler_tests/native/rustler_test/src/test_codegen.rs
@@ -54,6 +54,35 @@ pub fn map_echo(map: AddMap) -> AddMap {
     map
 }
 
+#[derive(NifMap)]
+pub struct RenamedMap {
+    #[rustler(rename = "type")]
+    type_: rustler::Atom,
+    start: u32,
+    #[rustler(rename = "end")]
+    end_: u32,
+    #[rustler(rename = "async")]
+    async_: bool,
+}
+
+#[rustler::nif]
+pub fn renamed_map_echo(map: RenamedMap) -> RenamedMap {
+    map
+}
+
+#[derive(NifMap)]
+pub struct UnicodeRenamedMap {
+    #[rustler(rename = "name_ä")]
+    name_a_umlaut: u32,
+    #[rustler(rename = "name_ö")]
+    name_o_umlaut: u32,
+}
+
+#[rustler::nif]
+pub fn unicode_renamed_map_echo(map: UnicodeRenamedMap) -> UnicodeRenamedMap {
+    map
+}
+
 #[derive(Debug, NifStruct)]
 #[must_use] // Added to test Issue #152
 #[module = "AddStruct"]
@@ -156,6 +185,21 @@ pub fn tagged_enum_4_echo(tagged_enum: TaggedEnum4) -> TaggedEnum4 {
     tagged_enum
 }
 
+#[derive(NifTaggedEnum)]
+pub enum RenamedTaggedEnum {
+    #[rustler(rename = "renamed")]
+    Named {
+        #[rustler(rename = "end")]
+        end_: i32,
+        y: i32,
+    },
+}
+
+#[rustler::nif]
+pub fn renamed_tagged_enum_echo(tagged_enum: RenamedTaggedEnum) -> RenamedTaggedEnum {
+    tagged_enum
+}
+
 #[derive(NifUntaggedEnum)]
 pub enum UntaggedEnum {
     Foo(u32),
diff --git a/rustler_tests/test/codegen_test.exs b/rustler_tests/test/codegen_test.exs
@@ -45,6 +45,16 @@ defmodule RustlerTest.CodegenTest do
       assert value == RustlerTest.map_echo(value)
     end
 
+    test "renamed fields" do
+      value = %{type: :import, start: 0, end: 12, async: true}
+      assert value == RustlerTest.renamed_map_echo(value)
+    end
+
+    test "renamed fields with unicode atoms" do
+      value = %{"name_ä": 1, "name_ö": 2}
+      assert value == RustlerTest.unicode_renamed_map_echo(value)
+    end
+
     test "with invalid map" do
       value = %{lhs: "invalid", rhs: 2, loc: {57, 15}}
 
@@ -330,6 +340,11 @@ defmodule RustlerTest.CodegenTest do
              end)
   end
 
+  test "renamed tagged enum variants and fields" do
+    value = {:renamed, %{end: 1, y: 2}}
+    assert value == RustlerTest.renamed_tagged_enum_echo(value)
+  end
+
   test "untagged enum transcoder" do
     assert 123 == RustlerTest.untagged_enum_echo(123)
     assert "Hello" == RustlerTest.untagged_enum_echo("Hello")
