anchor.diff:        if (comparison != null) {
           constraints.add(comparison);
           continue;
  -      }
  -
  -      var compatibleWith = matchCompatibleWith();
  -      if (compatibleWith != null) {
  -        return compatibleWith;
         }
   
         // If we got here, we couldn't parse the remaining string.
  
positive.code:   ///     <=5.1.4
    ///     >2.0.4 <= 2.4.6
    factory VersionConstraint.parse(String text) {
      // Handle the "any" constraint.
      if (text.trim() == "any") return any;
  
      var originalText = text;
      var constraints = [];
  
      skipWhitespace() {
        text = text.trim();
      }
  
      // Try to parse and consume a version number.
      matchVersion() {
  
negative.code:             '"$originalText", got "$text".');
        }
  
        if (text.isNotEmpty) {
          throw new FormatException('Cannot include other constraints with '
              '"^" constraint in "$originalText".');
        }
  
        return new VersionConstraint.compatibleWith(version);
      }
  
      var compatibleWith = matchCompatibleWith();
      if (compatibleWith != null) return compatibleWith;
  
      var constraints = [];
  
      while (true) {
        skipWhitespace();
  