dump label usages in go src

main.go

package main

import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
)

const dumpCode = false

func main() {
	panicOnError(filepath.Walk(path.Join(os.Getenv("GOROOT"), "src"),
		func(path string, info os.FileInfo, err error) error {
			if info.IsDir() {
				return nil
			}

			if filepath.Ext(path) == ".go" {
				dumpLabels(path)
			}
			return nil
		},
	))
}

func dumpLabels(file string) {
	var (
		data    = mustReadFile(file)
		fileSet = token.NewFileSet()
		f       = mustParse(fileSet, file, data)
	)

	ast.Inspect(f, func(n ast.Node) bool {
		if n == nil {
			return true
		}

		if label, ok := n.(*ast.LabeledStmt); ok {
			fmt.Printf("%v+%v - %s\n",
				file,
				fileSet.Position(n.Pos()).Line,
				label.Label.Name,
			)
			if dumpCode {
				fmt.Println(string(data[n.Pos()-1 : n.End()-1]))
				fmt.Println()
			}
		}
		return true
	})
}

func mustParse(fileSet *token.FileSet, file string, data []byte) *ast.File {
	f, err := parser.ParseFile(fileSet, file, data, parser.ParseComments)
	panicOnError(err)

	return f
}

func mustReadFile(file string) []byte {
	b, err := ioutil.ReadFile(file)
	panicOnError(err)

	return b
}
func panicOnError(err error) {
	if err != nil {
		panic(err)
	}
}