log.Printf("%s:%d: unexpected approval\n", filename, i+1)
				exitCode = 1
			}
		}
		nonblank = append(nonblank, line)
	}
	return nonblank
}

var fset = token.NewFileSet()

type Walker struct {
	context     *build.Context
	root        string
	scope       []string
	current     *apiPackage
	deprecated  map[token.Pos]bool
	features    map[string]bool              // set