}
	}
	if haveConstant {
		p.back()
		if p.have(scanner.Float) {
			if prefix != '$' {
				p.errorf("floating-point constant must be an immediate")
			}
			a.Type = obj.TYPE_FCONST
			a.Val = p.floatExpr()
			// fmt.Printf("FCONST %s\n", obj.Dconv(&emptyProg, 0, a))
			p.expectOperandEnd()
			return
		}
		if p.have(scanner.String) {
			if prefix != '$' {

			if macro != nil {
				nesting++
				in.invokeMacro(macro)
				continue
			}
			fallthrough
		default:
			if tok == scanner.EOF && len(in.ifdefStack) > 0 {
				// We're skipping text but have run out of input with no #endif.
				in.Error("unclosed #ifdef or #ifndef")
			}
			in.beginningOfLine = tok == '\n'
			if in.enabled() {
				in.text = in.Stack.Text()
				return tok
			}
		}
	}

	// limit (8KB), we stop growing the source string once the limit
	// is reached and keep reusing the same source string - that
	// should therefore be always resident in the L1 cache - until we
	// have completed the construction of the result.
	// This yields significant speedups (up to +100%) in cases where
	// the result length is large (roughly, over L2 cache size).
	const chunkLimit = 8 * 1024
	chunkMax := n

// invocation of F then behaves like a call to panic, terminating G's
// execution and running any deferred functions. This continues until all
// functions in the executing goroutine have stopped, in reverse order. At
// that point, the program is terminated with a non-zero exit code. This
// termination sequence is called panicking and can be controlled by the
// built-in function recover.
//

	}
	testValidHeader(&h, t)
}

// Issue 4393. It is valid to have an extra data header
// which contains no body.
func TestZeroLengthHeader(t *testing.T) {
	h := FileHeader{
		Name:   "extadata.txt",
		Method: Deflate,
		Extra: []byte{

// scanners.
func (s *Scanner) Scan() bool {
	if s.done {
		return false
	}
	s.scanCalled = true
	// Loop until we have a token.
	for {
		// See if we can get a token with what we already have.
		// If we've run out of data but have an error, give the split function
		// a chance to recover any remaining, possibly empty token.
		if s.end > s.start || s.err != nil {

then fixing the bug will break that code.
New features can also have similar impacts:
enabling the HTTP/2 use by the HTTP client broke programs
connecting to servers with buggy HTTP/2 implementations.
These kinds of changes are unavoidable and
[permitted by the Go 1 compatibility rules](/doc/go1compat).
Even so, Go provides a mechanism called GODEBUG to
reduce the impact such changes have on Go developers
using newer toolchains to compile old code.

// license that can be found in the LICENSE file.

package tar

import "strings"

// Format represents the tar archive format.
//
// The original tar format was introduced in Unix V7.
// Since then, there have been multiple competing formats attempting to
// standardize or extend the V7 format to overcome its limitations.
// The most common formats are the USTAR, PAX, and GNU formats,
// each with their own advantages and limitations.

	// IDs above that range are defined by third-party vendors.
	// Since ZIP lacked high precision timestamps (nor an official specification
	// of the timezone used for the date fields), many competing extra fields
	// have been invented. Pervasive use effectively makes them "official".
	//
	// See http://mdfs.net/Docs/Comp/Archiving/Zip/ExtraField
	zip64ExtraID       = 0x0001 // Zip64 extended information
	ntfsExtraID        = 0x000a // NTFS

	if err = r.init(f, fi.Size()); err != nil && err != ErrInsecurePath {
		f.Close()
		return nil, err
	}
	r.f = f
	return r, err
}

// NewReader returns a new [Reader] reading from r, which is assumed to
// have the given size in bytes.
//
// If any file inside the archive uses a non-local name
// (as defined by [filepath.IsLocal]) or a name containing backslashes
// and the GODEBUG environment variable contains `zipinsecurepath=0`,