const (
	// Deliberately hide the meaning of constants from public API.
	_ Format = (1 << iota) / 4 // Sequence of 0, 0, 1, 2, 4, 8, etc...

	// FormatUnknown indicates that the format is unknown.
	FormatUnknown

	// The format of the original Unix V7 tar tool prior to standardization.
	formatV7

	// FormatUSTAR represents the USTAR header format defined in POSIX.1-1988.
	//

pkg go/constant, const Float Kind
pkg go/constant, const Int = 3
pkg go/constant, const Int Kind
pkg go/constant, const String = 2
pkg go/constant, const String Kind
pkg go/constant, const Unknown = 0
pkg go/constant, const Unknown Kind
pkg go/constant, func BinaryOp(Value, token.Token, Value) Value
pkg go/constant, func BitLen(Value) int
pkg go/constant, func BoolVal(Value) bool
pkg go/constant, func Bytes(Value) []uint8

			r := testNonEmptyReader{strings.NewReader(maker.makeReg.str)}
			fr = &regFileReader{r, maker.makeReg.size}
			fr = &sparseFileReader{fr, sph, 0}
		default:
			t.Fatalf("test %d, unknown make operation: %T", i, maker)
		}

		for j, tf := range v.tests {
			switch tf := tf.(type) {
			case testRead:
				b := make([]byte, tf.cnt)
				n, err := fr.Read(b)

decide which.

The obvious thing for cgo to do is to process the preamble, expanding
#includes and processing the corresponding C code. That would require
a full C parser and type checker that was also aware of any extensions
known to the system compiler (for example, all the GNU C extensions) as
well as the system-specific header locations and system-specific
pre-#defined macros. This is certainly possible to do, but it is an
enormous amount of work.

		}
	case fm&fs.ModeNamedPipe != 0:
		h.Typeflag = TypeFifo
	case fm&fs.ModeSocket != 0:
		return nil, fmt.Errorf("archive/tar: sockets not supported")
	default:
		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
	}
	if fm&fs.ModeSetuid != 0 {
		h.Mode |= c_ISUID
	}
	if fm&fs.ModeSetgid != 0 {
		h.Mode |= c_ISGID
	}
	if fm&fs.ModeSticky != 0 {
		h.Mode |= c_ISVTX
	}

					}
				case testClose:
					err := tw.Close()
					if !equalError(err, tf.wantErr) {
						t.Fatalf("test %d, Close() = %v, want %v", i, err, tf.wantErr)
					}
				default:
					t.Fatalf("test %d, unknown test operation: %T", i, tf)
				}
			}

			if v.file != "" {
				want, err := os.ReadFile(v.file)
				if err != nil {
					t.Fatalf("ReadFile() = %v, want nil", err)
				}
				got := buf.Bytes()

			}
			buf.WriteByte(']')
		}

	case *types.TypeParam:
		// Type parameter names may change, so use a placeholder instead.
		fmt.Fprintf(buf, "$%d", typ.Index())

	default:
		panic(fmt.Sprintf("unknown type %T", typ))
	}
}

func (w *Walker) writeSignature(buf *bytes.Buffer, sig *types.Signature) {
	if tparams := sig.TypeParams(); tparams != nil {
		w.writeTypeParams(buf, tparams, true)
	}

---
title: "Go, Backwards Compatibility, and GODEBUG"
layout: article
---

<!--
This document is kept in the Go repo, not x/website,
because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.

		// to an index into the r.fileList entry that we are
		// building. They are used to mark duplicate entries.
		files := make(map[string]int)
		knownDirs := make(map[string]int)

		// dirs[name] is true if name is known to be a directory,
		// because it appears as a prefix in a path.
		dirs := make(map[string]bool)

		for _, file := range r.File {
			isDir := len(file.Name) > 0 && file.Name[len(file.Name)-1] == '/'

	instructions["BL"] = obj.ACALL
	// MCR differs from MRC by the way fields of the word are encoded.
	// (Details in arm.go). Here we add the instruction so parse will find
	// it, but give it an opcode number known only to us.
	instructions["MCR"] = aMCR

	return &Arch{
		LinkArch:       &arm.Linkarm,
		Instructions:   instructions,
		Register:       register,
		RegisterPrefix: registerPrefix,