Fix the unconditional usage of string interpolation in strum (#360)

Co-authored-by: Peter Glotfelty <peter@glotfelty.us>
Peternator7 · Jun 5, 2024 · a663c60 · a663c60
1 parent c89286f
commit a663c60
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Showing 2 changed files with 12 additions and 2 deletions.
diff --git a/strum_macros/src/macros/strings/display.rs b/strum_macros/src/macros/strings/display.rs
@@ -124,7 +124,17 @@ pub fn display_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
                         }
                     }
                 }
-                Fields::Unit => quote! { #name::#ident #params => ::core::fmt::Display::fmt(&format!(#output), f) }
+                Fields::Unit => {
+                    let used_vars = capture_format_strings(&output)?;
+                    if !used_vars.is_empty() {
+                        return Err(syn::Error::new_spanned(
+                            &output,
+                            "Unit variants do not support interpolation",
+                        ));
+                    }
+
+                    quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
+                }
             };
 
             arms.push(arm);

diff --git a/strum_nostd_tests/src/lib.rs b/strum_nostd_tests/src/lib.rs
@@ -5,7 +5,7 @@ mod tests {
     use core::str::FromStr;
     use strum::EnumString;
 
-    #[derive(Debug, Eq, PartialEq, EnumString)]
+    #[derive(Debug, Eq, PartialEq, EnumString, strum::Display)]
     enum Color {
         Red,
         Blue {