fix(join): add comma at the end of tuple statement to let rust recognize a _one elemnt tuple_

Author: mi-caren

benzina-derive/src/join/mod.rs

@@ -114,6 +114,14 @@ impl Transformation {
         quote! { ::benzina::__private::IndexMap::<_, (#(#values),*)> }
     }
 
+    fn tuple_from_vec(vec: Vec<impl ToTokens>) -> TokenStream {
+        if vec.is_empty() {
+            quote! { () }
+        } else {
+            quote! { (#(#vec),*,) }
+        }
+    }
+
     fn accumulator(&self, accumulator_index: Option<usize>) -> TokenStream {
         let accumulator_index = if let Some(accumulator_index) = accumulator_index {
             let accumulator_index = Index::from(accumulator_index);
@@ -140,7 +148,8 @@ impl Transformation {
             quote! {}
         };
 
-        let or_insert = self.or_insert(&tuple_index_overwrites);
+        let or_insert_tokens =
+            Transformation::tuple_from_vec(self.or_insert(&tuple_index_overwrites));
         let accumulator = self
             .entries
             .iter()
@@ -157,7 +166,7 @@ impl Transformation {
             #wrapper {
                 let mut accumulator = ::benzina::__private::indexmap::map::Entry::or_insert(
                     ::benzina::__private::IndexMap::entry(&mut #accumulator_index, #id),
-                    (#(#or_insert),*)
+                    #or_insert_tokens
                 );
                 #(#accumulator)*
             }