code: func TrimBuildFilesFromExcludes(excludes []string, dockerfile string, dockerfileFromStdin bool) []string {
  	if keep, _ := fileutils.Matches(".dockerignore", excludes); keep {
  		excludes = append(excludes, "!.dockerignore")
  	}
  	if keep, _ := fileutils.Matches(dockerfile, excludes); keep && !dockerfileFromStdin {
  		excludes = append(excludes, "!"+dockerfile)
  	}
  	return excludes
  }
docs: // TrimBuildFilesFromExcludes removes the named Dockerfile and .dockerignore from
  // the list of excluded files. The daemon will remove them from the final context
  // but they must be in available in the context when passed to the API.