Fix incorrect error message for #[display(opt)] on non-Option<T> tuple fields (2nd+) in #[derive(FromStr)].

Author: frozenlib

parse-display-derive/src/lib.rs

@@ -1063,11 +1063,11 @@ impl FieldKey {
             Member::Unnamed(index) => Self::Unnamed(index.index as usize),
         }
     }
-    fn from_field(field: &Field) -> Self {
+    fn from_field(index: usize, field: &Field) -> Self {
         if let Some(ident) = &field.ident {
             Self::from_ident(ident)
         } else {
-            Self::Unnamed(0)
+            Self::Unnamed(index)
         }
     }
 

parse-display-derive/src/parser_builder.rs

@@ -475,15 +475,15 @@ impl<'a> ParserBuilder<'a> {
         if !bounds.can_extend {
             return Ok(());
         }
-        for field in self.fields.values() {
+        for (index, field) in self.fields.values().enumerate() {
             let mut bounds = bounds.child(field.hattrs.bound_from_str_resolved());
             if bounds.can_extend && field.capture.is_some() && field.hattrs.with.is_none() {
                 let mut ty = &field.source.ty;
                 if field.hattrs.opt.value() {
                     if let Some(opt_ty) = get_option_element(ty) {
                         ty = opt_ty;
                     } else {
-                        let key = FieldKey::from_field(field.source);
+                        let key = FieldKey::from_field(index, field.source);
                         bail!(ty.span(), "field `{key}` is not a option type.");
                     }
                 }