message: syntax: add ClassUnicode::is_all_ascii
  This mirrors the same routine on ClassBytes. This is useful when
  translating an HIR to an NFA and one wants to write a fast path for the
  common all ASCII case.
diff: @@ -938,6 +938,13 @@ impl ClassUnicode {
  pub fn symmetric_difference(&mut self, other: &ClassUnicode) {
  self.set.symmetric_difference(&other.set);
  }
  +
  + /// Returns true if and only if this character class will either match
  + /// nothing or only ASCII bytes. Stated differently, this returns false
  + /// if and only if this class contains a non-ASCII codepoint.
  + pub fn is_all_ascii(&self) -> bool {
  + self.set.intervals().last().map_or(true, |r| r.end <= '\x7F')
  + }
  }
  /// An iterator over all ranges in a Unicode character class.
  