anchor.diff:  ///   to the [multiRootOutputPath], and assert that [multiRootOutputPath]
   ///   starts with `/packages` (more explanation inline).
   ///
  -// TODO(jmesserly): find a new home for this.
  +// TODO(#40251): Remove this logic from dev_compiler itself, push it to the
  +// invokers of dev_compiler which have more knowledge about how they want
  +// source paths to look.
   Map placeSourceMap(Map sourceMap, String sourceMapPath, String multiRootScheme,
       {String multiRootOutputPath, String sourceMapBase}) {
     var map = Map.from(sourceMap);
  
positive.code:   return uri;
  }
  
  /// Adjusts the source paths in [sourceMap] to be relative paths,and returns
  /// the new map.
  ///
  /// Relative paths are in terms of URIs ('/'), not local OS paths (e.g.,
  /// windows '\').
  ///
  /// Source uris show up in two forms, absolute `file:` uris and custom
  /// [multiRootScheme] uris (also "absolute" uris, but always relative to some
  
negative.code:         // `/packages` path, we do that by stripping the `/lib` prefix and
          // relying on the `multiRootOutputPath` to be set to the proper
          // packages dir (so /packages/<package>).
          if (shortPath.startsWith('/lib') &&
              multiRootOutputPath.startsWith('/packages')) {
            shortPath = shortPath.substring(4);
          }
          var multiRootPath = "${multiRootOutputPath ?? ''}$shortPath";
  