wantFormat.mayBe(FormatUSTAR) // PAX implies USTAR allowed too
		}
		format.mayOnlyBe(wantFormat) // Set union of formats allowed and format wanted
	}
	if format == FormatUnknown {
		switch h.Format {
		case FormatUSTAR:
			err = headerError{"Format specifies USTAR", whyNoUSTAR, whyOnlyPAX, whyOnlyGNU}
		case FormatPAX:
			err = headerError{"Format specifies PAX", whyNoPAX, whyOnlyGNU}
		case FormatGNU:

var panicOnError bool

func (p *Parser) errorf(format string, args ...interface{}) {
	if panicOnError {
		panic(fmt.Errorf(format, args...))
	}
	if p.lineNum == p.errorLine {
		// Only one error per line.
		return
	}
	p.errorLine = p.lineNum
	if p.lex != nil {
		// Put file and line information on head of message.
		format = "%s:%d: " + format + "\n"
		args = append([]interface{}{p.lex.File(), p.lineNum}, args...)

}

// Issue 4302.
func TestHeaderInvalidTagAndSize(t *testing.T) {
	const timeFormat = "20060102T150405.000.txt"

	ts := time.Now()
	filename := ts.Format(timeFormat)

	h := FileHeader{
		Name:   filename,
		Method: Deflate,
		Extra:  []byte(ts.Format(time.RFC3339Nano)), // missing tag and len, but Extra is best-effort parsing
	}
	h.SetModTime(ts)

	testValidHeader(&h, t)
}

			if err := tr.handleSparseFile(hdr, rawHdr); err != nil {
				return nil, err
			}

			// Set the final guess at the format.
			if format.has(FormatUSTAR) && format.has(FormatPAX) {
				format.mayOnlyBe(FormatUSTAR)
			}
			hdr.Format = format
			return hdr, nil // This is a file, so stop
		}
	}
}

// handleRegularFile sets up the current file reader and padding such that it

		fh.ModifiedDate, fh.ModifiedTime = timeToMsDosTime(fh.Modified)

		// Use "extended timestamp" format since this is what Info-ZIP uses.
		// Nearly every major ZIP implementation uses a different format,
		// but at least most seem to be able to understand the other formats.
		//
		// This format happens to be identical for both local and central header
		// if modification time is the only timestamp being encoded.

		formats: FormatUSTAR | FormatPAX,
	}, {
		header:  &Header{Size: 077777777777, Format: FormatGNU},
		formats: FormatGNU,
	}, {
		header:  &Header{Size: 077777777777 + 1},
		paxHdrs: map[string]string{paxSize: "8589934592"},
		formats: FormatPAX | FormatGNU,
	}, {
		header:  &Header{Size: 077777777777 + 1, Format: FormatPAX},
		paxHdrs: map[string]string{paxSize: "8589934592"},
		formats: FormatPAX,

				ModTime:  time.Unix(1254699560, 0),
				Format:   FormatGNU,
			}, nil},
		},
	}, {
		// This truncated file was produced using this library.
		// It was verified to work with GNU tar 1.27.1 and BSD tar 3.1.2.
		//  dd if=/dev/zero bs=1G count=16 >> writer-big-long.tar
		//  gnutar -xvf writer-big-long.tar
		//  bsdtar -xvf writer-big-long.tar
		//
		// This file is in PAX format.
		file: "testdata/writer-big-long.tar",

	}
	w.emitf("method (%s%s) %s%s", w.typeString(recv), tps, m.Obj().Name(), w.signatureString(sig))
}

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 {

while still insisting that races are errors and that tools can diagnose and report them.
</p>

<h2 id="model">Memory Model</h2>

<p>
The following formal definition of Go's memory model closely follows
the approach presented by Hans-J. Boehm and Sarita V. Adve in
“<a href="https://www.hpl.hp.com/techreports/2008/HPL-2008-56.pdf">Foundations of the C++ Concurrency Memory Model</a>”,