Function Example_text

stack/example_test.go:29–128

Runs a crashing program and converts it to a dense text format like pp does.

()

// Runs a crashing program and converts it to a dense text format like pp does.
func Example_text() {
	source := `package main

	import "time"

	func main() {
		c := crashy{}
		go func() {
			c.die(42.)
		}()
		select {}
	}

	type crashy struct{}

	func (c crashy) die(f float32) {
		time.Sleep(time.Millisecond)
		panic(int(f))
	}`

	// Skipped error handling to make the example shorter.
	root, _ := os.MkdirTemp("", "stack")
	defer os.RemoveAll(root)
	p := filepath.Join(root, "main.go")
	os.WriteFile(p, []byte(source), 0600)
	// Disable both optimization (-N) and inlining (-l).
	c := exec.Command("go", "run", "-gcflags", "-N -l", p)
	// This is important, otherwise only the panicking goroutine will be printed.
	c.Env = append(os.Environ(), "GOTRACEBACK=1")
	raw, _ := c.CombinedOutput()
	stream := bytes.NewReader(raw)

	s, suffix, err := stack.ScanSnapshot(stream, os.Stdout, stack.DefaultOpts())
	if err != nil && err != io.EOF {
		log.Fatal(err)
	}

	// Find out similar goroutine traces and group them into buckets.
	buckets := s.Aggregate(stack.AnyValue).Buckets

	// Calculate alignment.
	srcLen := 0
	pkgLen := 0
	for _, bucket := range buckets {
		for _, line := range bucket.Signature.Stack.Calls {
			if l := len(fmt.Sprintf("%s:%d", line.SrcName, line.Line)); l > srcLen {
				srcLen = l
			}
			if l := len(filepath.Base(line.Func.ImportPath)); l > pkgLen {
				pkgLen = l
			}
		}
	}

	for _, bucket := range buckets {
		// Print the goroutine header.
		extra := ""
		if s := bucket.SleepString(); s != "" {