and it may store non-pointer data, C pointers, or Go pointers to pinned
memory through those pointers. It may not store a Go pointer to unpinned
memory in memory pointed to by a C pointer (which again, implies that it
may not store a string, slice, channel, and so forth). A Go function
called by C code may take a Go pointer but it must preserve the property
that the Go memory to which it points (and the Go memory to which that

	if err != nil {
		if list, ok := err.(scanner.ErrorList); ok {
			// If err is a scanner.ErrorList, its String will print just
			// the first error and then (+n more errors).
			// Instead, turn it into a new Error that will return
			// details for all the errors.
			for _, e := range list {
				fmt.Fprintln(os.Stderr, e)
			}
			os.Exit(2)
		}
		fatalf("parsing %s: %s", name, err)
	}
	return ast1
}

type panicReader struct{ panic bool }

func (r panicReader) Read(p []byte) (int, error) {
	if r.panic {
		panic("oops")
	}
	return 0, io.EOF
}

// Make sure that an empty Buffer remains empty when
// it is "grown" before a Read that panics
func TestReadFromPanicReader(t *testing.T) {

	// First verify non-panic behaviour
	var buf Buffer
	i, err := buf.ReadFrom(panicReader{})
	if err != nil {
		t.Fatal(err)

// internal buffer only needs to be resliced.
// It returns the index where bytes should be written and whether it succeeded.
func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
	if l := len(b.buf); n <= cap(b.buf)-l {
		b.buf = b.buf[:l+n]
		return l, true
	}
	return 0, false
}

// grow grows the buffer to guarantee space for n more bytes.
// It returns the index where bytes should be written.

// Some fields may not be populated.
//
// For forward compatibility, users that retrieve a Header from Reader.Next,
// mutate it in some ways, and then pass it back to Writer.WriteHeader
// should do so by creating a new Header and copying the fields
// that they are interested in preserving.
type Header struct {
	// Typeflag is the type of header entry.

	// write a zip file
	buf := new(bytes.Buffer)
	w := NewWriter(buf)

	for _, wt := range writeTests {
		testCreate(t, w, &wt)
	}

	if err := w.Close(); err != nil {
		t.Fatal(err)
	}

	// read it back
	r, err := NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))
	if err != nil {
		t.Fatal(err)
	}
	for i, wt := range writeTests {
		testReadFile(t, r.File[i], &wt)
	}
}

//
// Otherwise, the [Scanner] advances the input. If the token is not nil,
// the [Scanner] returns it to the user. If the token is nil, the
// Scanner reads more data and continues scanning; if there is no more
// data--if atEOF was true--the [Scanner] returns. If the data does not
// yet hold a complete token, for instance if it has no newline while
// scanning lines, a [SplitFunc] can return (0, nil, nil) to signal the

field is only used during parsing, when it is populated with policy OIDs, but
not used during marshaling. It can be used to marshal these larger OIDs, instead
of the existing PolicyIdentifiers field, by using the
[`x509usepolicies` setting.](/pkg/crypto/x509/#CreateCertificate).


### Go 1.21

Go 1.21 made it a run-time error to call `panic` with a nil interface value,

are defined for all architectures: if the compiler doesn't generate it, it might not be there.
If you need to use a missing instruction, there are two ways to proceed.
One is to update the assembler to support that instruction, which is straightforward
but only worthwhile if it's likely the instruction will be used again.
Instead, for simple one-off cases, it's possible to use the <code>BYTE</code>
and <code>WORD</code> directives

	extraLen := int(b.uint16())
	return int64(fileHeaderLen + filenameLen + extraLen), nil
}

// readDirectoryHeader attempts to read a directory header from r.
// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
// and ErrFormat if it doesn't find a valid header signature.
func readDirectoryHeader(f *File, r io.Reader) error {
	var buf [directoryHeaderLen]byte
	if _, err := io.ReadFull(r, buf[:]); err != nil {