The [GODEBUG History](#history) gives the exact defaults for each Go toolchain version.
For example, Go 1.21 introduces the `panicnil` setting,
controlling whether `panic(nil)` is allowed;
it defaults to `panicnil=0`, making `panic(nil)` a run-time error.
Using `panicnil=1` restores the behavior of Go 1.20 and earlier.

When compiling a work module or workspace that declares

func TestNegativeRead(t *testing.T) {
	// should panic with a description pointing at the reader, not at itself.
	// (should NOT panic with slice index error, for example.)
	b := NewReader(new(negativeReader))
	defer func() {
		switch err := recover().(type) {
		case nil:
			t.Fatal("read did not panic")
		case error:

}

func (w *Walker) emitf(format string, args ...any) {
	f := strings.Join(w.scope, ", ") + ", " + fmt.Sprintf(format, args...)
	if strings.Contains(f, "\n") {
		panic("feature contains newlines: " + f)
	}

	if _, dup := w.features[f]; dup {
		panic("duplicate feature inserted: " + f)
	}
	w.features[f] = true

	if verbose {
		log.Printf("feature: %s", f)
	}
}

//
// f(NewDummyDataGen(100, 0)) == f(NewDummyDataGen(50, 0)) + f(NewDummyDataGen(50, 50))
func NewDummyDataGen(totalLength, skipOffset int64) io.ReadSeeker {
	if totalLength < 0 {
		panic("Negative length passed to DummyDataGen!")
	}
	if skipOffset < 0 {
		panic("Negative rotations are not allowed")
	}

	skipOffset %= int64(len(alphabets))
	const multiply = 100
	as := bytes.Repeat(alphabets, multiply)

	success := lm.unlock(isWriteLock)
	if !success {
		panic("Trying to Unlock() while no Lock() is active")
	}
}

// RUnlock releases a read lock held on lm.
//
// It is a run-time error if lm is not locked on entry to RUnlock.
func (lm *LRWMutex) RUnlock() {
	isWriteLock := false
	success := lm.unlock(isWriteLock)
	if !success {
		panic("Trying to RUnlock() while no RLock() is active")
	}
}

func (s *Singleton[T]) IsSet() bool {
	select {
	case <-s.set:
		return true
	default:
		return false
	}
}

// Set the value and unblock all Get requests.
// This may only be called once, a second call will panic.
func (s *Singleton[T]) Set(v *T) {
	s.v = v
	close(s.set)

	br := bufio.NewReader(bytes.NewReader(b))
loop:
	for {
		_, err := br.ReadByte()
		switch err {
		case nil:
			continue loop
		case io.EOF:
			break loop
		default:
			panic(err)
		}
	}
}

func BenchmarkScanner(b *testing.B) {
	b.Run("small", func(b *testing.B) {
		for b.Loop() {
			benchmarkScanner(smallInput)
		}
	})
	b.Run("medium", func(b *testing.B) {

			t.Fatalf("Test %d: ciphertext mismatch: got %x - want %x", i, key.Ciphertext, test.Key.Ciphertext)
		}
	}
}

func mustDecodeB64(s string) []byte {
	b, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b

	if b.r > 0 {
		copy(b.buf, b.buf[b.r:b.w])
		b.w -= b.r
		b.r = 0
	}

	if b.w >= len(b.buf) {
		panic("bufio: tried to fill full buffer")
	}

	// Read new data: try a limited number of times.
	for i := maxConsecutiveEmptyReads; i > 0; i-- {
		n, err := b.rd.Read(b.buf[b.w:])
		if n < 0 {
			panic(errNegativeRead)
		}
		b.w += n
		if err != nil {
			b.err = err
			return
		}
		if n > 0 {

			// it's possible that a future update to the CSRs in inst.go could introduce
			// a conflict. This check ensures that such a conflict does not go
			// unnoticed.
			if _, ok := riscv64SpecialOperand[csrName]; ok {
				panic(fmt.Sprintf("riscv64 special operand %q redefined", csrName))
			}
			riscv64SpecialOperand[csrName] = riscv.SpecialOperand(int(csrCode) + int(riscv.SPOP_CSR_BEGIN))
		}
		// Add the FENCE operands