anchor.diff:      final line = _getLineFromTokenPos(script, tokenPos);
   
       if (line == null) {
  -      stderr.writeln(
  -          'tokenPos $tokenPos in function ${funcRef.name} has no line mapping '
  -          'for script ${script.uri!}');
  +      if (_debugTokenPositions) {
  +        stderr.writeln(
  +            'tokenPos $tokenPos in function ${funcRef.name} has no line '
  +            'mapping for script ${script.uri!}');
  +      }
         return;
       }
       hits.funcNames![line] = funcName;
  
positive.code:       for (final pos in tokenPositions) {
          final line = reportLines ? pos : _getLineFromTokenPos(script!, pos);
          if (line == null) {
            stderr
                .write('tokenPos $pos has no line mapping for script $scriptUri');
            continue;
          }
          body(line);
  
negative.code: import 'hitmap.dart';
  
  const _retryInterval = Duration(milliseconds: 200);
  const _debugTokenPositions = bool.fromEnvironment('DEBUG_COVERAGE');
  
  /// Collects coverage for all isolates in the running VM.
  ///
  