// users may pass to 'go test'.
func ShortTestFlags() []string {
	testing.Init()

	var names []string
	flag.VisitAll(func(f *flag.Flag) {
		var name string
		var found bool
		if name, found = strings.CutPrefix(f.Name, "test."); !found {
			return
		}

		switch name {
		case "testlogfile", "paniconexit0", "fuzzcachedir", "fuzzworker", "gocoverdir":
			// These flags are only for use by cmd/go.
		default:

func (c *ChaCha8) UnmarshalBinary(data []byte) error {
	data, ok := cutPrefix(data, []byte("readbuf:"))
	if ok {
		var buf []byte
		buf, data, ok = readUint8LengthPrefixed(data)
		if !ok {
			return errors.New("invalid ChaCha8 Read buffer encoding")
		}
		c.readLen = copy(c.readBuf[len(c.readBuf)-len(buf):], buf)
	}
	return chacha8rand.Unmarshal(&c.state, data)
}

func cutPrefix(s, prefix []byte) (after []byte, found bool) {

}

func ExampleCutPrefix() {
	show := func(s, sep string) {
		after, found := strings.CutPrefix(s, sep)
		fmt.Printf("CutPrefix(%q, %q) = %q, %v\n", s, sep, after, found)
	}
	show("Gopher", "Go")
	show("Gopher", "ph")
	// Output:
	// CutPrefix("Gopher", "Go") = "pher", true
	// CutPrefix("Gopher", "ph") = "Gopher", false
}

func ExampleCutSuffix() {
	show := func(s, sep string) {

	t.Helper()

	c := strings.SplitN(output, "\n", 2)
	if len(c) == 1 {
		t.Fatalf("expected at least one complete line in the output, got:\n%s", output)
	}
	expect, ok := strings.CutPrefix(c[0], "expect: ")
	if !ok {
		t.Fatalf("expected first line of output to start with \"expect: \", got: %q", c[0])
	}
	rest := c[1]
	if expect == "OK" && rest != "OK\n" {

	listCmd := testenv.Command(t, goBin, "list", "std", "cmd")
	out, err := listCmd.Output()
	if err != nil {
		t.Fatal(err)
	}
	for _, fullPkg := range strings.Split(string(out), "\n") {
		pkg, found := strings.CutPrefix(fullPkg, "vendor/")
		if !found {
			_, pkg, found = strings.Cut(fullPkg, "/vendor/")
			if !found {
				continue
			}
		}
		if !isAllowed(pkg) {
			t.Errorf(`

		}
	}
	return -1
}

func Cut(s, sep string) (before, after string, found bool) {
	if i := Index(s, sep); i >= 0 {
		return s[:i], s[i+len(sep):], true
	}
	return s, "", false
}

func CutPrefix(s, prefix string) (after string, found bool) {
	if !HasPrefix(s, prefix) {
		return s, false
	}
	return s[len(prefix):], true
}

func CutSuffix(s, suffix string) (before string, found bool) {

	}
	recurseThenCallGo(w, frames, goroutines-1, main)
}

func goroutineID() string {
	buf := make([]byte, 128)
	runtime.Stack(buf, false)
	prefix := []byte("goroutine ")
	var found bool
	if buf, found = bytes.CutPrefix(buf, prefix); !found {
		panic(fmt.Sprintf("expected %q at beginning of traceback:\n%s", prefix, buf))
	}
	id, _, _ := bytes.Cut(buf, []byte(" "))
	return string(id)

			return list
		}
		text = text[2 : len(text)-2] // cut /* and */
	} else if strings.HasPrefix(list[0].Text, "//") {
		kind = "//"
		var b strings.Builder
		for _, c := range list {
			after, found := strings.CutPrefix(c.Text, "//")
			if !found {
				return list
			}
			// Accumulate //go:build etc lines separately.
			if isDirective(after) {
				directives = append(directives, c)
				continue
			}

			}

			if annotations, ok := strings.CutPrefix(line, "## "); ok {
				// Metadata. Take the union of annotations across multiple lines, if present.
				meta := vendorMeta[mod]
				for _, entry := range strings.Split(annotations, ";") {
					entry = strings.TrimSpace(entry)
					if entry == "explicit" {
						meta.Explicit = true
					}
					if goVersion, ok := strings.CutPrefix(entry, "go "); ok {
						meta.GoVersion = goVersion

		// At least one of the errors in errList should match the current error.
		indices = indices[:0]
		for i, want := range errList {
			pattern, substr := strings.CutPrefix(want.text, " ERROR ")
			if !substr {
				var found bool
				pattern, found = strings.CutPrefix(want.text, " ERRORx ")
				if !found {
					panic("unreachable")
				}
			}
			unquoted, err := strconv.Unquote(strings.TrimSpace(pattern))
			if err != nil {