anchor.diff:      return new DartPlatform.universal(reason: 'All libraries agree');
     }
   
  +  if (primaryLibrary != null && libraries[primaryLibrary].worksEverywhere) {
  +    return new DartPlatform.universal(
  +        reason: 'primary library - `$primaryLibrary`');
  +  }
  +
     final items = libraries.values
         .where((p) => !p.worksEverywhere)
         .expand((p) => p.restrictedTo)
  
positive.code:   if (transitiveLibs == null) {
      return new DartPlatform.conflict('failed to scan transitive libraries');
    }
    final libraries = new Map.fromIterable(transitiveLibs.keys ?? <String>[],
        value: (key) => classifyLibPlatform(transitiveLibs[key]));
    final primaryLibrary =
        _selectPrimaryLibrary(pubspec, transitiveLibs.keys.toSet());
  
negative.code: 
    if (primaryLibrary != null) {
      var primaryPlatform = libraries[primaryLibrary];
      if (primaryPlatform.restrictedTo?.length == 1) {
        return new DartPlatform.withRestrictions(primaryPlatform.restrictedTo,
            reason: 'primary library - `$primaryLibrary`');
      }
  