fix: correctly format trait function with multiple where clauses

tooling/nargo_fmt/src/formatter/traits.rs

@@ -300,6 +300,23 @@ mod tests {
         assert_format(src, expected);
     }
 
+    #[test]
+    fn format_trait_with_function_with_multiple_where_clauses() {
+        let src = " mod moo { trait Foo { 
+            fn  foo<T> () where  A: B, C: D;
+         } }";
+        let expected = "mod moo {
+    trait Foo {
+        fn foo<T>()
+        where
+            A: B,
+            C: D;
+    }
+}
+";
+        assert_format(src, expected);
+    }
+
     #[test]
     fn format_trait_with_function_with_visibility() {
         let src = " mod moo { trait Foo { 

tooling/nargo_fmt/src/formatter/where_clause.rs

@@ -23,7 +23,8 @@ impl<'a> Formatter<'a> {
         // To format it we'll have to skip the second type `F` if we find a `+` token.
         let mut write_type = true;
 
-        for constraint in constraints {
+        let constrains_len = constraints.len();
+        for (index, constraint) in constraints.into_iter().enumerate() {
             if write_type {
                 self.write_line();
                 self.write_indentation();
@@ -45,7 +46,9 @@ impl<'a> Formatter<'a> {
 
             write_type = true;
 
-            if self.is_at(Token::Comma) {
+            if index < constrains_len - 1 {
+                self.write_token(Token::Comma);
+            } else if self.is_at(Token::Comma) {
                 if write_trailing_comma_and_new_line {
                     self.write_token(Token::Comma);
                 } else {