ability specify additional trait bounds for Visit trait

Author: mrDIMAS

fyrox-core-derive/src/visit.rs

@@ -120,7 +120,8 @@ fn impl_visit_enum(ty_args: &args::TypeArgs, variant_args: &[args::VariantArgs])
                 }
             });
 
-        let (impl_generics, ty_generics, where_clause) = ty_args.generics.split_for_impl();
+        let generics = ty_args.impl_generics();
+        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
         quote! {
             fn id #impl_generics (me: &#ty_ident #ty_generics) -> #id_type #where_clause {
@@ -178,7 +179,8 @@ fn impl_visit_enum(ty_args: &args::TypeArgs, variant_args: &[args::VariantArgs])
                 }
             });
 
-        let (impl_generics, ty_generics, where_clause) = ty_args.generics.split_for_impl();
+        let generics = ty_args.impl_generics();
+        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
         quote! {
             fn from_id #impl_generics (

fyrox-core-derive/src/visit/args.rs

@@ -33,6 +33,23 @@ pub struct TypeArgs {
     pub pre_visit_method: Option<Ident>,
     #[darling(default)]
     pub post_visit_method: Option<Ident>,
+    /// Custom `Visit` impl type boundary.
+    #[darling(default)]
+    pub bounds: Option<Vec<WherePredicate>>,
+}
+
+impl TypeArgs {
+    pub fn impl_generics(&self) -> Generics {
+        let mut generics = self.generics.clone();
+
+        let clause = generics.make_where_clause();
+
+        if let Some(bounds) = &self.bounds {
+            clause.predicates.extend(bounds.iter().cloned());
+        }
+
+        generics
+    }
 }
 
 /// Parsed from struct's or enum variant's field