Implement a suffix attribute for serialization of enum variants (#440)

amogh-dambal · web-flow · commit bb1339026b44 · 2025-06-29T16:58:29.000-07:00
* test: add default test for prefix kw * feat: implement suffix enum attribute similarly to the `prefix` attribute, implement a corresponding attribute that suffixes enum variants. issue: fixes #392 * test: add tests for new suffix attribute * test: add tests checking prefix + suffix attributes together * style: run cargo fmt * doc: update docs for new suffix attribute
diff --git a/strum_macros/src/helpers/metadata.rs b/strum_macros/src/helpers/metadata.rs
@@ -19,6 +19,7 @@ pub mod kw {
     custom_keyword!(const_into_str);
     custom_keyword!(use_phf);
     custom_keyword!(prefix);
+    custom_keyword!(suffix);
     custom_keyword!(parse_err_ty);
     custom_keyword!(parse_err_fn);
 
@@ -56,6 +57,10 @@ pub enum EnumMeta {
         kw: kw::prefix,
         prefix: LitStr,
     },
+    Suffix {
+        kw: kw::suffix,
+        suffix: LitStr,
+    },
     ParseErrTy {
         kw: kw::parse_err_ty,
         path: Path,
@@ -94,6 +99,11 @@ impl Parse for EnumMeta {
             input.parse::<Token![=]>()?;
             let prefix = input.parse()?;
             Ok(EnumMeta::Prefix { kw, prefix })
+        } else if lookahead.peek(kw::suffix) {
+            let kw = input.parse::<kw::suffix>()?;
+            input.parse::<Token![=]>()?;
+            let suffix = input.parse()?;
+            Ok(EnumMeta::Suffix { kw, suffix })
         } else if lookahead.peek(kw::parse_err_ty) {
             let kw = input.parse::<kw::parse_err_ty>()?;
             input.parse::<Token![=]>()?;
diff --git a/strum_macros/src/helpers/type_props.rs b/strum_macros/src/helpers/type_props.rs
@@ -24,6 +24,7 @@ pub struct StrumTypeProperties {
     pub discriminant_vis: Option<Visibility>,
     pub use_phf: bool,
     pub prefix: Option<LitStr>,
+    pub suffix: Option<LitStr>,
     pub enum_repr: Option<TokenStream>,
     pub const_into_str: bool,
     pub discriminant_docs: Vec<LitStr>,
@@ -43,6 +44,7 @@ impl HasTypeProperties for DeriveInput {
         let mut use_phf_kw = None;
         let mut crate_module_path_kw = None;
         let mut prefix_kw = None;
+        let mut suffix_kw = None;
         let mut const_into_str = None;
 
         for meta in strum_meta {
@@ -90,6 +92,14 @@ impl HasTypeProperties for DeriveInput {
                     prefix_kw = Some(kw);
                     output.prefix = Some(prefix);
                 }
+                EnumMeta::Suffix { suffix, kw } => {
+                    if let Some(fst_kw) = suffix_kw {
+                        return Err(occurrence_error(fst_kw, kw, "suffix"));
+                    }
+
+                    suffix_kw = Some(kw);
+                    output.suffix = Some(suffix);
+                }
                 EnumMeta::ParseErrTy { path, kw } => {
                     if let Some(fst_kw) = parse_err_ty_kw {
                         return Err(occurrence_error(fst_kw, kw, "parse_err_ty"));
diff --git a/strum_macros/src/helpers/variant_props.rs b/strum_macros/src/helpers/variant_props.rs
@@ -35,6 +35,7 @@ impl StrumVariantProperties {
         &self,
         case_style: Option<CaseStyle>,
         prefix: Option<&LitStr>,
+        suffix: Option<&LitStr>,
     ) -> LitStr {
         let mut output = self.to_string.as_ref().cloned().unwrap_or_else(|| {
             self.serialize
@@ -48,6 +49,10 @@ impl StrumVariantProperties {
             output = LitStr::new(&(prefix.value() + &output.value()), output.span());
         }
 
+        if let Some(suffix) = suffix {
+            output = LitStr::new(&(output.value() + &suffix.value()), output.span());
+        }
+
         output
     }
 
diff --git a/strum_macros/src/lib.rs b/strum_macros/src/lib.rs
@@ -180,6 +180,18 @@ pub fn from_string(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 ///
 /// assert_eq!("/redred", ColorWithPrefix::Red.as_ref());
 /// assert_eq!("/Green", ColorWithPrefix::Green.as_ref());
+///
+/// // With suffix on all variants
+/// #[derive(AsRefStr, Debug)]
+/// #[strum(suffix = ".rs")]
+/// enum ColorWithSuffix {
+///     #[strum(serialize = "redred")]
+///     Red,
+///     Green,
+/// }
+///
+/// assert_eq!("redred.rs", ColorWithSuffix::Red.as_ref());
+/// assert_eq!("Green.rs", ColorWithSuffix::Green.as_ref());
 /// ```
 #[proc_macro_derive(AsRefStr, attributes(strum))]
 pub fn as_ref_str(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
@@ -381,7 +393,9 @@ pub fn to_string(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 /// 3. The name of the variant will be used if there are no `serialize` or `to_string` attributes.
 /// 4. If the enum has a `strum(prefix = "some_value_")`, every variant will have that prefix prepended
 ///    to the serialization.
-/// 5. Enums with fields support string interpolation.
+/// 5. If the enum has a `strum(suffix = "_another_value")`, every variant will have that suffix appended
+///    to the serialization.
+/// 6. Enums with fields support string interpolation.
 ///    Note this means the variant will not "round trip" if you then deserialize the string.
 ///
 ///    ```rust
diff --git a/strum_macros/src/macros/enum_variant_names.rs b/strum_macros/src/macros/enum_variant_names.rs
@@ -22,8 +22,11 @@ pub fn enum_variant_names_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
         .iter()
         .map(|v| {
             let props = v.get_variant_properties()?;
-            Ok(props
-                .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref()))
+            Ok(props.get_preferred_name(
+                type_properties.case_style,
+                type_properties.prefix.as_ref(),
+                type_properties.suffix.as_ref(),
+            ))
         })
         .collect::<syn::Result<Vec<LitStr>>>()?;
 
diff --git a/strum_macros/src/macros/strings/as_ref_str.rs b/strum_macros/src/macros/strings/as_ref_str.rs
@@ -40,8 +40,11 @@ where
         // Look at all the serialize attributes.
         // Use `to_string` attribute (not `as_ref_str` or something) to keep things consistent
         // (i.e. always `enum.as_ref().to_string() == enum.to_string()`).
-        let output = variant_properties
-            .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref());
+        let output = variant_properties.get_preferred_name(
+            type_properties.case_style,
+            type_properties.prefix.as_ref(),
+            type_properties.suffix.as_ref(),
+        );
         let params = match variant.fields {
             Fields::Unit => quote! {},
             Fields::Unnamed(..) => quote! { (..) },
diff --git a/strum_macros/src/macros/strings/display.rs b/strum_macros/src/macros/strings/display.rs
@@ -36,8 +36,11 @@ pub fn display_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
         }
 
         // Look at all the serialize attributes.
-        let output = variant_properties
-            .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref());
+        let output = variant_properties.get_preferred_name(
+            type_properties.case_style,
+            type_properties.prefix.as_ref(),
+            type_properties.suffix.as_ref(),
+        );
 
         let params = match variant.fields {
             Fields::Unit => quote! {},
diff --git a/strum_macros/src/macros/strings/mod.rs b/strum_macros/src/macros/strings/mod.rs
@@ -23,7 +23,7 @@ where
         Fields::Unnamed(f) if f.unnamed.len() == 1 => {
             let ident = &quote! { field0 };
             let ref_kw = match f.unnamed.last().unwrap().ty {
-                syn::Type::Reference(..) => quote! { },
+                syn::Type::Reference(..) => quote! {},
                 _ => quote! { ref },
             };
 
@@ -33,7 +33,7 @@ where
         Fields::Named(f) if f.named.len() == 1 => {
             let field = f.named.last().unwrap();
             let ref_kw = match field.ty {
-                syn::Type::Reference(..) => quote! { },
+                syn::Type::Reference(..) => quote! {},
                 _ => quote! { ref },
             };
 
diff --git a/strum_macros/src/macros/strings/to_string.rs b/strum_macros/src/macros/strings/to_string.rs
@@ -39,8 +39,11 @@ pub fn to_string_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
         }
 
         // Look at all the serialize attributes.
-        let output = variant_properties
-            .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref());
+        let output = variant_properties.get_preferred_name(
+            type_properties.case_style,
+            type_properties.prefix.as_ref(),
+            type_properties.suffix.as_ref(),
+        );
 
         let params = match variant.fields {
             Fields::Unit => quote! {},
diff --git a/strum_tests/tests/as_ref_str.rs b/strum_tests/tests/as_ref_str.rs
@@ -1,7 +1,7 @@
 #![allow(deprecated)]
 
 use std::str::FromStr;
-use strum::{AsRefStr, AsStaticRef, AsStaticStr, EnumString, IntoStaticStr};
+use strum::{AsRefStr, AsStaticRef, AsStaticStr, Display, EnumString, IntoStaticStr};
 
 mod core {} // ensure macros call `::core`
 
@@ -61,7 +61,13 @@ fn as_green_str() {
 #[test]
 fn as_fuchsia_str() {
     assert_eq!("Purple", (Color::Inner(InnerColor::Purple)).as_ref());
-    assert_eq!("Purple", (Color::InnerField { inner: InnerColor::Purple }).as_ref());
+    assert_eq!(
+        "Purple",
+        (Color::InnerField {
+            inner: InnerColor::Purple
+        })
+        .as_ref()
+    );
 }
 
 #[derive(IntoStaticStr)]
@@ -128,7 +134,9 @@ enum Brightness {
     #[strum(transparent)]
     Gray(&'static str),
     #[strum(transparent)]
-    Grey { inner: &'static str }
+    Grey {
+        inner: &'static str,
+    },
 }
 
 #[test]
@@ -145,7 +153,10 @@ fn brightness_serialize_all() {
     assert_eq!("dim", <&'static str>::from(Brightness::Dim { glow: 0 }));
     assert_eq!("Bright", <&'static str>::from(Brightness::BrightWhite));
     assert_eq!("Gray", <&'static str>::from(Brightness::Gray("Gray")));
-    assert_eq!("Grey", <&'static str>::from(Brightness::Grey { inner: "Grey" }));
+    assert_eq!(
+        "Grey",
+        <&'static str>::from(Brightness::Grey { inner: "Grey" })
+    );
 }
 
 #[derive(IntoStaticStr)]
@@ -226,3 +237,38 @@ fn test_const_into_static_str() {
     const BRIGHT_WHITE: &'static str = BrightnessConst::BrightWhite.into_str();
     assert_eq!("Bright", BRIGHT_WHITE);
 }
+
+#[derive(AsRefStr, Display, EnumString)]
+#[strum(prefix = "/etc/data/assets/", suffix = ".json")]
+enum Asset {
+    #[strum(serialize = "cfg", serialize = "configuration", to_string = "config")]
+    Config,
+    #[strum(serialize = "params")]
+    Params,
+    #[strum(default)]
+    Generic(String),
+}
+
+#[test]
+fn test_prefix_and_suffix() {
+    assert_eq!(
+        String::from("/etc/data/assets/config.json"),
+        (Asset::Config).to_string()
+    );
+    assert_eq!("/etc/data/assets/config.json", (Asset::Config).as_ref(),);
+
+    assert_eq!(
+        String::from("/etc/data/assets/params.json"),
+        (Asset::Params).to_string()
+    );
+    assert_eq!("/etc/data/assets/params.json", (Asset::Params).as_ref());
+
+    assert_eq!(
+        String::from("some-file"),
+        (Asset::Generic("some-file".into()).to_string()),
+    );
+    assert_eq!(
+        "/etc/data/assets/Generic.json",
+        (Asset::Generic("()".into()).as_ref()),
+    )
+}
diff --git a/strum_tests/tests/from_str.rs b/strum_tests/tests/from_str.rs
@@ -31,7 +31,7 @@ enum Color {
 #[derive(Debug, Eq, PartialEq, EnumString, strum::Display)]
 enum Color2 {
     #[strum(default)]
-    Purple { inner: String }
+    Purple { inner: String },
 }
 
 fn assert_from_str<'a, T>(a: T, from: &'a str)
@@ -72,8 +72,19 @@ fn color_default() {
 
 #[test]
 fn color2_default() {
-    assert_from_str(Color2::Purple { inner: String::from("test") }, "test");
-    assert_eq!(String::from("test"), Color2::Purple { inner: String::from("test") }.to_string());
+    assert_from_str(
+        Color2::Purple {
+            inner: String::from("test"),
+        },
+        "test",
+    );
+    assert_eq!(
+        String::from("test"),
+        Color2::Purple {
+            inner: String::from("test")
+        }
+        .to_string()
+    );
 }
 
 #[test]
diff --git a/strum_tests/tests/prefix.rs b/strum_tests/tests/prefix.rs
@@ -20,3 +20,16 @@ fn prefix_redred() {
     assert_eq!(String::from("colour/RedRed"), (Color::Red).to_string());
     assert_eq!(("colour/RedRed"), (Color::Red).as_ref());
 }
+
+#[test]
+fn prefix_green_default() {
+    assert_eq!(
+        String::from("green"),
+        (Color::Green("green".into())).to_string()
+    );
+
+    assert_eq!(
+        String::from("colour/Green"),
+        (Color::Green("green".into())).as_ref()
+    );
+}
diff --git a/strum_tests/tests/suffix.rs b/strum_tests/tests/suffix.rs
@@ -0,0 +1,44 @@
+use strum::{Display, EnumString};
+use strum_macros::AsRefStr;
+
+#[allow(dead_code)]
+#[derive(Debug, EnumString, Display, AsRefStr)]
+#[strum(suffix = ".color")]
+enum Color {
+    #[strum(to_string = "RedRed")]
+    Red,
+    #[strum(serialize = "b", to_string = "blue")]
+    Blue { hue: usize },
+    #[strum(serialize = "y", serialize = "yellow")]
+    Yellow,
+    #[strum(default)]
+    Green(String),
+}
+
+#[test]
+fn suffix_redred() {
+    let c = Color::Red;
+    assert_eq!(String::from("RedRed.color"), c.to_string());
+    assert_eq!("RedRed.color", c.as_ref());
+}
+
+#[test]
+fn suffix_blue() {
+    let c = Color::Blue { hue: 10 };
+    assert_eq!(String::from("blue.color"), c.to_string());
+    assert_eq!("blue.color", c.as_ref());
+}
+
+#[test]
+fn suffix_yellow() {
+    let c = Color::Yellow;
+    assert_eq!(String::from("yellow.color"), c.to_string());
+    assert_eq!("yellow.color", c.as_ref());
+}
+
+#[test]
+fn suffix_green_default() {
+    let c = Color::Green("basic-green".into());
+    assert_eq!(String::from("basic-green"), c.to_string());
+    assert_eq!("Green.color", c.as_ref());
+}
