message: Improve pretty printing of empty sequences
diff: @@ -272,10 +272,13 @@ impl<'interner, 'arena> Context<'interner, 'arena> {
  fn sequence(
  &'arena self,
  start_delim: DocBuilder<'arena, Self>,
  - docs: impl Iterator<Item = DocBuilder<'arena, Self>> + Clone,
  + docs: impl ExactSizeIterator<Item = DocBuilder<'arena, Self>> + Clone,
  separator: DocBuilder<'arena, Self>,
  end_delim: DocBuilder<'arena, Self>,
  ) -> DocBuilder<'arena, Self> {
  + if docs.len() == 0 {
  + self.concat([start_delim, end_delim])
  + } else {
  DocBuilder::flat_alt(
  self.concat([
  start_delim.clone(),
  @@ -297,6 +300,7 @@ impl<'interner, 'arena> Context<'interner, 'arena> {
  )
  }
  }
  +}
  impl<'interner, 'arena, A: 'arena> DocAllocator<'arena, A> for Context<'interner, 'arena> {
  type Doc = RefDoc<'arena, A>;
  