f.walk(ast1, ctxProg, (*File).saveExport)
	f.walk(ast2, ctxProg, (*File).saveExport2)

	f.Comments = ast1.Comments
	f.AST = ast2
}

// Like ast.CommentGroup's Text method but preserves
// leading blank lines, so that line numbers line up.
func commentText(g *ast.CommentGroup) string {
	var pieces []string
	for _, com := range g.List {
		c := com.Text
		// Remove comment markers.

	{"4", func(b *Reader) string { return reads(b, 4) }},
	{"5", func(b *Reader) string { return reads(b, 5) }},
	{"7", func(b *Reader) string { return reads(b, 7) }},
	{"bytes", readBytes},
	{"lines", readLines},
}

const minReadBufferSize = 16

var bufsizes = []int{
	0, minReadBufferSize, 23, 32, 46, 64, 93, 128, 1024, 4096,
}

func TestReader(t *testing.T) {
	var texts [31]string

pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VGLAB ideal-int
pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VINES = 2989
pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VINESECHO = 2991
pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VINESECHO ideal-int
pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VINES ideal-int
pkg syscall (netbsd-arm64-cgo), const ETHERTYPE_VINESLOOP = 2990

		return nil, err
	}
	return bytes.TrimSpace(out), nil
}

func getLines(cmd *exec.Cmd) [][]byte {
	out := output(cmd)
	lines := bytes.Split(out, []byte("\n"))
	// Skip the empty line at the end.
	if len(lines[len(lines)-1]) == 0 {
		lines = lines[:len(lines)-1]
	}
	return lines
}

func output(cmd *exec.Cmd) []byte {
	out, err := cmd.Output()
	if err != nil {
		fmt.Println(strings.Join(cmd.Args, "\n"))

Each file is a list of API features, one per line.

go1.txt (and similarly named files) are frozen once a version has been
shipped. Each file adds new lines but does not remove any.

except.txt lists features that may disappear without breaking true
compatibility.

Starting with go1.19.txt, each API feature line must end in "#nnnnn"

	lineNum       int   // Line number in source file.
	errorLine     int   // Line number of last error.
	errorCount    int   // Number of errors.
	sawCode       bool  // saw code in this file (as opposed to comments and blank lines)
	pc            int64 // virtual PC; count of Progs; doesn't advance for GLOBL or DATA.
	input         []lex.Token
	inputPos      int
	pendingLabels []string // Labels to attach to next instruction.

pkg syscall (darwin-386), const IPPROTO_TRUNK1 = 23
pkg syscall (darwin-386), const IPPROTO_TRUNK2 = 24
pkg syscall (darwin-386), const IPPROTO_TTP = 84
pkg syscall (darwin-386), const IPPROTO_VINES = 83
pkg syscall (darwin-386), const IPPROTO_VISA = 70
pkg syscall (darwin-386), const IPPROTO_VMTP = 81
pkg syscall (darwin-386), const IPPROTO_WBEXPAK = 79
pkg syscall (darwin-386), const IPPROTO_WBMON = 78

	{
		"argumented macro invoked without arguments",
		lines(
			"#define X() foo ",
			"X()",
			"X",
		),
		"foo.\n.X.\n",
	},
	{
		"multiline macro without arguments",
		lines(
			"#define A 1\\",
			"\t2\\",
			"\t3",
			"before",
			"A",
			"after",
		),
		"before.\n.1.\n.2.\n.3.\n.after.\n",
	},
	{
		"multiline macro with arguments",
		lines(
			"#define A(a, b, c) a\\",
			"\tb\\",

	data, err := os.ReadFile(input)
	if err != nil {
		t.Error(err)
		return
	}
	lineno := 0
	seq := 0
	hexByLine := map[string]string{}
	lines := strings.SplitAfter(string(data), "\n")
Diff:
	for _, line := range lines {
		lineno++

		// Ignore include of textflag.h.
		if strings.HasPrefix(line, "#include ") {
			continue
		}

		// Ignore GLOBL.

pkg go/build, type Package struct, Directives []Directive #56986
pkg go/build, type Package struct, TestDirectives []Directive #56986
pkg go/build, type Package struct, XTestDirectives []Directive #56986
pkg go/token, method (*File) Lines() []int #57708
pkg go/types, method (*Package) GoVersion() string #61175
pkg html/template, const ErrJSTemplate = 12 #59584
pkg html/template, const ErrJSTemplate ErrorCode #59584