Fix field transparency for top-level shared attribute in Display (#438

)

CHANGELOG.md

@@ -34,6 +34,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   ([#431](https://github.com/JelteF/derive_more/pull/431))
 - Incorrect rendering of raw identifiers as field names in `Debug` expansions.
   ([#431](https://github.com/JelteF/derive_more/pull/431))
+- Top-level `#[display("...")]` attribute on an enum not working transparently
+  for directly specified fields.
+  ([#438](https://github.com/JelteF/derive_more/pull/438))
 
 
 ## 1.0.0 - 2024-08-07

impl/src/fmt/debug.rs

@@ -13,7 +13,7 @@ use crate::utils::{
 
 use super::{
     trait_name_to_attribute_name, ContainerAttributes, ContainsGenericsExt as _,
-    FieldsExt as _, FmtAttribute,
+    FmtAttribute,
 };
 
 /// Expands a [`fmt::Debug`] derive macro.
@@ -250,23 +250,17 @@ impl Expansion<'_> {
     /// [`Debug::fmt()`]: std::fmt::Debug::fmt()
     fn generate_body(&self) -> syn::Result<TokenStream> {
         if let Some(fmt) = &self.attr.fmt {
-            return Ok(if let Some((expr, trait_ident)) = fmt.transparent_call() {
-                let expr = if let Some(field) = self
-                    .fields
-                    .fmt_args_idents()
-                    .find(|field| expr == *field || expr == field.unraw())
+            return Ok(
+                if let Some((expr, trait_ident)) =
+                    fmt.transparent_call_on_fields(self.fields)
                 {
-                    quote! { #field }
+                    quote! { derive_more::core::fmt::#trait_ident::fmt(#expr, __derive_more_f) }
                 } else {
-                    quote! { &(#expr) }
-                };
-
-                quote! { derive_more::core::fmt::#trait_ident::fmt(#expr, __derive_more_f) }
-            } else {
-                let deref_args = fmt.additional_deref_args(self.fields);
+                    let deref_args = fmt.additional_deref_args(self.fields);
 
-                quote! { derive_more::core::write!(__derive_more_f, #fmt, #(#deref_args),*) }
-            });
+                    quote! { derive_more::core::write!(__derive_more_f, #fmt, #(#deref_args),*) }
+                },
+            );
         };
 
         match self.fields {

impl/src/fmt/display.rs

@@ -11,7 +11,7 @@ use crate::utils::{attr::ParseMultiple as _, Spanning};
 
 use super::{
     trait_name_to_attribute_name, ContainerAttributes, ContainsGenericsExt as _,
-    FieldsExt as _, FmtAttribute,
+    FmtAttribute,
 };
 
 /// Expands a [`fmt::Display`]-like derive macro.
@@ -291,17 +291,9 @@ impl Expansion<'_> {
                     let deref_args = fmt.additional_deref_args(self.fields);
 
                     quote! { &derive_more::core::format_args!(#fmt, #(#deref_args),*) }
-                } else if let Some((expr, trait_ident)) = fmt.transparent_call() {
-                    let expr = if let Some(field) = self
-                        .fields
-                        .fmt_args_idents()
-                        .find(|field| expr == *field || expr == field.unraw())
-                    {
-                        quote! { #field }
-                    } else {
-                        quote! { &(#expr) }
-                    };
-
+                } else if let Some((expr, trait_ident)) =
+                    fmt.transparent_call_on_fields(self.fields)
+                {
                     quote! { derive_more::core::fmt::#trait_ident::fmt(#expr, __derive_more_f) }
                 } else {
                     let deref_args = fmt.additional_deref_args(self.fields);
@@ -358,8 +350,14 @@ impl Expansion<'_> {
             if let Some(shared_fmt) = &self.shared_attr {
                 let deref_args = shared_fmt.additional_deref_args(self.fields);
 
-                let shared_body = quote! {
-                    derive_more::core::write!(__derive_more_f, #shared_fmt, #(#deref_args),*)
+                let shared_body = if let Some((expr, trait_ident)) =
+                    shared_fmt.transparent_call_on_fields(self.fields)
+                {
+                    quote! { derive_more::core::fmt::#trait_ident::fmt(#expr, __derive_more_f) }
+                } else {
+                    quote! {
+                        derive_more::core::write!(__derive_more_f, #shared_fmt, #(#deref_args),*)
+                    }
                 };
 
                 body = if body.is_empty() {

impl/src/fmt/mod.rs

@@ -13,6 +13,7 @@ use quote::{format_ident, quote, ToTokens};
 use syn::{
     ext::IdentExt as _,
     parse::{Parse, ParseStream},
+    parse_quote,
     punctuated::Punctuated,
     spanned::Spanned as _,
     token,
@@ -199,6 +200,30 @@ impl FmtAttribute {
         Some((expr, format_ident!("{trait_name}")))
     }
 
+    /// Same as [`transparent_call()`], but additionally checks the returned [`Expr`] whether it's
+    /// one of the [`fmt_args_idents`] of the provided [`syn::Fields`], and makes it suitable for
+    /// passing directly into the transparent call of the delegated formatting trait.
+    ///
+    /// [`fmt_args_idents`]: FieldsExt::fmt_args_idents
+    /// [`transparent_call()`]: FmtAttribute::transparent_call
+    fn transparent_call_on_fields(
+        &self,
+        fields: &syn::Fields,
+    ) -> Option<(Expr, syn::Ident)> {
+        self.transparent_call().map(|(expr, trait_ident)| {
+            let expr = if let Some(field) = fields
+                .fmt_args_idents()
+                .find(|field| expr == *field || expr == field.unraw())
+            {
+                field.into()
+            } else {
+                parse_quote! { &(#expr) }
+            };
+
+            (expr, trait_ident)
+        })
+    }
+
     /// Returns an [`Iterator`] over bounded [`syn::Type`]s (and correspondent trait names) by this
     /// [`FmtAttribute`].
     fn bounded_types<'a>(