message: Use a consistent style for separating with commas
  Summary: It's a pretty common thing to do, and we were using two different styles, so better to move to the style that most code seems to have shifted to.
diff: @@ -82,11 +82,8 @@ where
  fn collect_repr(&self, s: &mut String) {
  s.push('(');
  - let mut first = true;
  - for v in &self.content {
  - if first {
  - first = false;
  - } else {
  + for (i, v) in self.content.iter().enumerate() {
  + if i != 0 {
  s.push_str(", ");
  }
  v.collect_repr(s);
  