Do not put where clause on a single with multi-lined type
@@ -656,6 +656,7 @@ pub fn format_impl(
if !contains_comment(&snippet[open_pos..])
&& items.is_empty()
&& generics.where_clause.predicates.len() == 1
+ && !result.contains('\n')
{
option.suppress_comma();
option.snuggle();
