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

@@ -4,6 +4,8 @@ use proc_macro2::{Span, TokenStream};
 use quote::{ToTokens, quote};
 use syn::{Ident, Index, Token, punctuated::Punctuated};
 
+use crate::join::utils::tuple_from_vec;
+
 use self::{
     quantity::Quantity,
     utils::{Identifiable, NewIndexMap},
@@ -140,7 +142,7 @@ impl Transformation {
             quote! {}
         };
 
-        let or_insert = self.or_insert(&tuple_index_overwrites);
+        let or_insert_tokens = tuple_from_vec(&self.or_insert(&tuple_index_overwrites));
         let accumulator = self
             .entries
             .iter()
@@ -157,7 +159,7 @@ 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)*
             }

benzina-derive/src/join/utils.rs

@@ -25,3 +25,11 @@ impl<T: ToTokens> ToTokens for Identifiable<T> {
         });
     }
 }
+
+pub(super) fn tuple_from_vec(vec: &[impl ToTokens]) -> TokenStream {
+    if vec.is_empty() {
+        quote! { () }
+    } else {
+        quote! { (#(#vec),*,) }
+    }
+}