Add a test for #2087

Author: topecongiro

tests/source/macros.rs

@@ -21,6 +21,12 @@ fn main() {
     kaas!(/* comments */ a /* post macro */, b /* another */);
 
     trailingcomma!( a , b , c , );
+    // Preserve trailing comma only when necessary.
+    ok!(file.seek(
+        SeekFrom::Start(
+            table.map(|table| fixture.offset(table)).unwrap_or(0),
+        )
+    ));
 
     noexpr!( i am not an expression, OK? );
 

tests/target/macros.rs

@@ -33,6 +33,10 @@ fn main() {
     );
 
     trailingcomma!(a, b, c,);
+    // Preserve trailing comma only when necessary.
+    ok!(file.seek(SeekFrom::Start(
+        table.map(|table| fixture.offset(table)).unwrap_or(0),
+    )));
 
     noexpr!( i am not an expression, OK? );