src/cmd/pack/pack_test.go - go - Git at Google

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 import (
 	"bufio"
 	"bytes"
 	"cmd/internal/archive"
 	"fmt"
 	"internal/testenv"
 	"io"
 	"io/fs"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"testing"
 	"time"
 )

 // testCreate creates an archive in the specified directory.
 func testCreate(t *testing.T, dir string) {
 	name := filepath.Join(dir, "pack.a")
 	ar := openArchive(name, os.O_RDWR|os.O_CREATE, nil)
 	// Add an entry by hand.
 	ar.addFile(helloFile.Reset())
 	ar.a.File().Close()
 	// Now check it.
 	ar = openArchive(name, os.O_RDONLY, []string{helloFile.name})
 	var buf bytes.Buffer
 	stdout = &buf
 	verbose = true
 	defer func() {
 		stdout = os.Stdout
 		verbose = false
 	}()
 	ar.scan(ar.printContents)
 	ar.a.File().Close()
 	result := buf.String()
 	// Expect verbose output plus file contents.
 	expect := fmt.Sprintf("%s\n%s", helloFile.name, helloFile.contents)
 	if result != expect {
 		t.Fatalf("expected %q got %q", expect, result)
 	}
 }

 // Test that we can create an archive, write to it, and get the same contents back.
 // Tests the rv and then the pv command on a new archive.
 func TestCreate(t *testing.T) {
 	dir := t.TempDir()
 	testCreate(t, dir)
 }

 // Test that we can create an archive twice with the same name (Issue 8369).
 func TestCreateTwice(t *testing.T) {
 	dir := t.TempDir()
 	testCreate(t, dir)
 	testCreate(t, dir)
 }

 // Test that we can create an archive, put some files in it, and get back a correct listing.
 // Tests the tv command.
 func TestTableOfContents(t *testing.T) {
 	dir := t.TempDir()
 	name := filepath.Join(dir, "pack.a")
 	ar := openArchive(name, os.O_RDWR|os.O_CREATE, nil)

 	// Add some entries by hand.
 	ar.addFile(helloFile.Reset())
 	ar.addFile(goodbyeFile.Reset())
 	ar.a.File().Close()

 	// Now print it.
 	var buf bytes.Buffer
 	stdout = &buf
 	verbose = true
 	defer func() {
 		stdout = os.Stdout
 		verbose = false
 	}()
 	ar = openArchive(name, os.O_RDONLY, nil)
 	ar.scan(ar.tableOfContents)
 	ar.a.File().Close()
 	result := buf.String()
 	// Expect verbose listing.
 	expect := fmt.Sprintf("%s\n%s\n", helloFile.Entry(), goodbyeFile.Entry())
 	if result != expect {
 		t.Fatalf("expected %q got %q", expect, result)
 	}

 	// Do it again without verbose.
 	verbose = false
 	buf.Reset()
 	ar = openArchive(name, os.O_RDONLY, nil)
 	ar.scan(ar.tableOfContents)
 	ar.a.File().Close()
 	result = buf.String()
 	// Expect non-verbose listing.
 	expect = fmt.Sprintf("%s\n%s\n", helloFile.name, goodbyeFile.name)
 	if result != expect {
 		t.Fatalf("expected %q got %q", expect, result)
 	}

 	// Do it again with file list arguments.
 	verbose = false
 	buf.Reset()
 	ar = openArchive(name, os.O_RDONLY, []string{helloFile.name})
 	ar.scan(ar.tableOfContents)
 	ar.a.File().Close()
 	result = buf.String()
 	// Expect only helloFile.
 	expect = fmt.Sprintf("%s\n", helloFile.name)
 	if result != expect {
 		t.Fatalf("expected %q got %q", expect, result)
 	}
 }

 // Test that we can create an archive, put some files in it, and get back a file.
 // Tests the x command.
 func TestExtract(t *testing.T) {
 	dir := t.TempDir()
 	name := filepath.Join(dir, "pack.a")
 	ar := openArchive(name, os.O_RDWR|os.O_CREATE, nil)
 	// Add some entries by hand.
 	ar.addFile(helloFile.Reset())
 	ar.addFile(goodbyeFile.Reset())
 	ar.a.File().Close()
 	// Now extract one file. We chdir to the directory of the archive for simplicity.
 	pwd, err := os.Getwd()
 	if err != nil {
 		t.Fatal("os.Getwd: ", err)
 	}
 	err = os.Chdir(dir)
 	if err != nil {
 		t.Fatal("os.Chdir: ", err)
 	}
 	defer func() {
 		err := os.Chdir(pwd)
 		if err != nil {
 			t.Fatal("os.Chdir: ", err)
 		}
 	}()
 	ar = openArchive(name, os.O_RDONLY, []string{goodbyeFile.name})
 	ar.scan(ar.extractContents)
 	ar.a.File().Close()
 	data, err := os.ReadFile(goodbyeFile.name)
 	if err != nil {
 		t.Fatal(err)
 	}
 	// Expect contents of file.
 	result := string(data)
 	expect := goodbyeFile.contents
 	if result != expect {
 		t.Fatalf("expected %q got %q", expect, result)
 	}
 }

 // Test that pack-created archives can be understood by the tools.
 func TestHello(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	dir := t.TempDir()
 	hello := filepath.Join(dir, "hello.go")
 	prog := `
 		package main
 		func main() {
 			println("hello world")
 		}
 	`
 	err := os.WriteFile(hello, []byte(prog), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	run := func(args ...string) string {
 		return doRun(t, dir, args...)
 	}

 	goBin := testenv.GoToolPath(t)
 	run(goBin, "build", "cmd/pack") // writes pack binary to dir
 	run(goBin, "tool", "compile", "hello.go")
 	run("./pack", "grc", "hello.a", "hello.o")
 	run(goBin, "tool", "link", "-o", "a.out", "hello.a")
 	out := run("./a.out")
 	if out != "hello world\n" {
 		t.Fatalf("incorrect output: %q, want %q", out, "hello world\n")
 	}
 }

 // Test that pack works with very long lines in PKGDEF.
 func TestLargeDefs(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping in -short mode")
 	}
 	testenv.MustHaveGoBuild(t)

 	dir := t.TempDir()
 	large := filepath.Join(dir, "large.go")
 	f, err := os.Create(large)
 	if err != nil {
 		t.Fatal(err)
 	}
 	b := bufio.NewWriter(f)

 	printf := func(format string, args ...interface{}) {
 		_, err := fmt.Fprintf(b, format, args...)
 		if err != nil {
 			t.Fatalf("Writing to %s: %v", large, err)
 		}
 	}

 	printf("package large\n\ntype T struct {\n")
 	for i := 0; i < 1000; i++ {
 		printf("f%d int `tag:\"", i)
 		for j := 0; j < 100; j++ {
 			printf("t%d=%d,", j, j)
 		}
 		printf("\"`\n")
 	}
 	printf("}\n")
 	if err = b.Flush(); err != nil {
 		t.Fatal(err)
 	}
 	if err = f.Close(); err != nil {
 		t.Fatal(err)
 	}

 	main := filepath.Join(dir, "main.go")
 	prog := `
 		package main
 		import "large"
 		var V large.T
 		func main() {
 			println("ok")
 		}
 	`
 	err = os.WriteFile(main, []byte(prog), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	run := func(args ...string) string {
 		return doRun(t, dir, args...)
 	}

 	goBin := testenv.GoToolPath(t)
 	run(goBin, "build", "cmd/pack") // writes pack binary to dir
 	run(goBin, "tool", "compile", "large.go")
 	run("./pack", "grc", "large.a", "large.o")
 	run(goBin, "tool", "compile", "-I", ".", "main.go")
 	run(goBin, "tool", "link", "-L", ".", "-o", "a.out", "main.o")
 	out := run("./a.out")
 	if out != "ok\n" {
 		t.Fatalf("incorrect output: %q, want %q", out, "ok\n")
 	}
 }

 // Test that "\n!\n" inside export data doesn't result in a truncated
 // package definition when creating a .a archive from a .o Go object.
 func TestIssue21703(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	dir := t.TempDir()

 	const aSrc = `package a; const X = "\n!\n"`
 	err := os.WriteFile(filepath.Join(dir, "a.go"), []byte(aSrc), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	const bSrc = `package b; import _ "a"`
 	err = os.WriteFile(filepath.Join(dir, "b.go"), []byte(bSrc), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	run := func(args ...string) string {
 		return doRun(t, dir, args...)
 	}

 	goBin := testenv.GoToolPath(t)
 	run(goBin, "build", "cmd/pack") // writes pack binary to dir
 	run(goBin, "tool", "compile", "a.go")
 	run("./pack", "c", "a.a", "a.o")
 	run(goBin, "tool", "compile", "-I", ".", "b.go")
 }

 // Test the "c" command can "see through" the archive generated by the compiler.
 // This is peculiar. (See issue #43271)
 func TestCreateWithCompilerObj(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	dir := t.TempDir()
 	src := filepath.Join(dir, "p.go")
 	prog := "package p; var X = 42\n"
 	err := os.WriteFile(src, []byte(prog), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	run := func(args ...string) string {
 		return doRun(t, dir, args...)
 	}

 	goBin := testenv.GoToolPath(t)
 	run(goBin, "build", "cmd/pack") // writes pack binary to dir
 	run(goBin, "tool", "compile", "-pack", "-o", "p.a", "p.go")
 	run("./pack", "c", "packed.a", "p.a")
 	fi, err := os.Stat(filepath.Join(dir, "p.a"))
 	if err != nil {
 		t.Fatalf("stat p.a failed: %v", err)
 	}
 	fi2, err := os.Stat(filepath.Join(dir, "packed.a"))
 	if err != nil {
 		t.Fatalf("stat packed.a failed: %v", err)
 	}
 	// For compiler-generated object file, the "c" command is
 	// expected to get (essentially) the same file back, instead
 	// of packing it into a new archive with a single entry.
 	if want, got := fi.Size(), fi2.Size(); want != got {
 		t.Errorf("packed file with different size: want %d, got %d", want, got)
 	}

 	// Test -linkobj flag as well.
 	run(goBin, "tool", "compile", "-linkobj", "p2.a", "-o", "p.x", "p.go")
 	run("./pack", "c", "packed2.a", "p2.a")
 	fi, err = os.Stat(filepath.Join(dir, "p2.a"))
 	if err != nil {
 		t.Fatalf("stat p2.a failed: %v", err)
 	}
 	fi2, err = os.Stat(filepath.Join(dir, "packed2.a"))
 	if err != nil {
 		t.Fatalf("stat packed2.a failed: %v", err)
 	}
 	if want, got := fi.Size(), fi2.Size(); want != got {
 		t.Errorf("packed file with different size: want %d, got %d", want, got)
 	}

 	run("./pack", "c", "packed3.a", "p.x")
 	fi, err = os.Stat(filepath.Join(dir, "p.x"))
 	if err != nil {
 		t.Fatalf("stat p.x failed: %v", err)
 	}
 	fi2, err = os.Stat(filepath.Join(dir, "packed3.a"))
 	if err != nil {
 		t.Fatalf("stat packed3.a failed: %v", err)
 	}
 	if want, got := fi.Size(), fi2.Size(); want != got {
 		t.Errorf("packed file with different size: want %d, got %d", want, got)
 	}
 }

 // Test the "r" command creates the output file if it does not exist.
 func TestRWithNonexistentFile(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	dir := t.TempDir()
 	src := filepath.Join(dir, "p.go")
 	prog := "package p; var X = 42\n"
 	err := os.WriteFile(src, []byte(prog), 0666)
 	if err != nil {
 		t.Fatal(err)
 	}

 	run := func(args ...string) string {
 		return doRun(t, dir, args...)
 	}

 	goBin := testenv.GoToolPath(t)
 	run(goBin, "build", "cmd/pack") // writes pack binary to dir
 	run(goBin, "tool", "compile", "-o", "p.o", "p.go")
 	run("./pack", "r", "p.a", "p.o") // should succeed
 }

 // doRun runs a program in a directory and returns the output.
 func doRun(t *testing.T, dir string, args ...string) string {
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Dir = dir
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("%v: %v\n%s", args, err, string(out))
 	}
 	return string(out)
 }

 // Fake implementation of files.

 var helloFile = &FakeFile{
 	name:     "hello",
 	contents: "hello world", // 11 bytes, an odd number.
 	mode:     0644,
 }

 var goodbyeFile = &FakeFile{
 	name:     "goodbye",
 	contents: "Sayonara, Jim", // 13 bytes, another odd number.
 	mode:     0644,
 }

 // FakeFile implements FileLike and also fs.FileInfo.
 type FakeFile struct {
 	name     string
 	contents string
 	mode     fs.FileMode
 	offset   int
 }

 // Reset prepares a FakeFile for reuse.
 func (f *FakeFile) Reset() *FakeFile {
 	f.offset = 0
 	return f
 }

 // FileLike methods.

 func (f *FakeFile) Name() string {
 	// A bit of a cheat: we only have a basename, so that's also ok for FileInfo.
 	return f.name
 }

 func (f *FakeFile) Stat() (fs.FileInfo, error) {
 	return f, nil
 }

 func (f *FakeFile) Read(p []byte) (int, error) {
 	if f.offset >= len(f.contents) {
 		return 0, io.EOF
 	}
 	n := copy(p, f.contents[f.offset:])
 	f.offset += n
 	return n, nil
 }

 func (f *FakeFile) Close() error {
 	return nil
 }

 // fs.FileInfo methods.

 func (f *FakeFile) Size() int64 {
 	return int64(len(f.contents))
 }

 func (f *FakeFile) Mode() fs.FileMode {
 	return f.mode
 }

 func (f *FakeFile) ModTime() time.Time {
 	return time.Time{}
 }

 func (f *FakeFile) IsDir() bool {
 	return false
 }

 func (f *FakeFile) Sys() interface{} {
 	return nil
 }

 // Special helpers.

 func (f *FakeFile) Entry() *archive.Entry {
 	return &archive.Entry{
 		Name:  f.name,
 		Mtime: 0, // Defined to be zero.
 		Uid:   0, // Ditto.
 		Gid:   0, // Ditto.
 		Mode:  f.mode,
 		Data:  archive.Data{Size: int64(len(f.contents))},
 	}
 }
	// Copyright 2014 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	import (
	"bufio"
	"bytes"
	"cmd/internal/archive"
	"fmt"
	"internal/testenv"
	"io"
	"io/fs"
	"os"
	"os/exec"
	"path/filepath"
	"testing"
	"time"
	)

	// testCreate creates an archive in the specified directory.
	func testCreate(t *testing.T, dir string) {
	name := filepath.Join(dir, "pack.a")
	ar := openArchive(name, os.O_RDWR\|os.O_CREATE, nil)
	// Add an entry by hand.
	ar.addFile(helloFile.Reset())
	ar.a.File().Close()
	// Now check it.
	ar = openArchive(name, os.O_RDONLY, []string{helloFile.name})
	var buf bytes.Buffer
	stdout = &buf
	verbose = true
	defer func() {
	stdout = os.Stdout
	verbose = false
	}()
	ar.scan(ar.printContents)
	ar.a.File().Close()
	result := buf.String()
	// Expect verbose output plus file contents.
	expect := fmt.Sprintf("%s\n%s", helloFile.name, helloFile.contents)
	if result != expect {
	t.Fatalf("expected %q got %q", expect, result)
	}
	}

	// Test that we can create an archive, write to it, and get the same contents back.
	// Tests the rv and then the pv command on a new archive.
	func TestCreate(t *testing.T) {
	dir := t.TempDir()
	testCreate(t, dir)
	}

	// Test that we can create an archive twice with the same name (Issue 8369).
	func TestCreateTwice(t *testing.T) {
	dir := t.TempDir()
	testCreate(t, dir)
	testCreate(t, dir)
	}

	// Test that we can create an archive, put some files in it, and get back a correct listing.
	// Tests the tv command.
	func TestTableOfContents(t *testing.T) {
	dir := t.TempDir()
	name := filepath.Join(dir, "pack.a")
	ar := openArchive(name, os.O_RDWR\|os.O_CREATE, nil)

	// Add some entries by hand.
	ar.addFile(helloFile.Reset())
	ar.addFile(goodbyeFile.Reset())
	ar.a.File().Close()

	// Now print it.
	var buf bytes.Buffer
	stdout = &buf
	verbose = true
	defer func() {
	stdout = os.Stdout
	verbose = false
	}()
	ar = openArchive(name, os.O_RDONLY, nil)
	ar.scan(ar.tableOfContents)
	ar.a.File().Close()
	result := buf.String()
	// Expect verbose listing.
	expect := fmt.Sprintf("%s\n%s\n", helloFile.Entry(), goodbyeFile.Entry())
	if result != expect {
	t.Fatalf("expected %q got %q", expect, result)
	}

	// Do it again without verbose.
	verbose = false
	buf.Reset()
	ar = openArchive(name, os.O_RDONLY, nil)
	ar.scan(ar.tableOfContents)
	ar.a.File().Close()
	result = buf.String()
	// Expect non-verbose listing.
	expect = fmt.Sprintf("%s\n%s\n", helloFile.name, goodbyeFile.name)
	if result != expect {
	t.Fatalf("expected %q got %q", expect, result)
	}

	// Do it again with file list arguments.
	verbose = false
	buf.Reset()
	ar = openArchive(name, os.O_RDONLY, []string{helloFile.name})
	ar.scan(ar.tableOfContents)
	ar.a.File().Close()
	result = buf.String()
	// Expect only helloFile.
	expect = fmt.Sprintf("%s\n", helloFile.name)
	if result != expect {
	t.Fatalf("expected %q got %q", expect, result)
	}
	}

	// Test that we can create an archive, put some files in it, and get back a file.
	// Tests the x command.
	func TestExtract(t *testing.T) {
	dir := t.TempDir()
	name := filepath.Join(dir, "pack.a")
	ar := openArchive(name, os.O_RDWR\|os.O_CREATE, nil)
	// Add some entries by hand.
	ar.addFile(helloFile.Reset())
	ar.addFile(goodbyeFile.Reset())
	ar.a.File().Close()
	// Now extract one file. We chdir to the directory of the archive for simplicity.
	pwd, err := os.Getwd()
	if err != nil {
	t.Fatal("os.Getwd: ", err)
	}
	err = os.Chdir(dir)
	if err != nil {
	t.Fatal("os.Chdir: ", err)
	}
	defer func() {
	err := os.Chdir(pwd)
	if err != nil {
	t.Fatal("os.Chdir: ", err)
	}
	}()
	ar = openArchive(name, os.O_RDONLY, []string{goodbyeFile.name})
	ar.scan(ar.extractContents)
	ar.a.File().Close()
	data, err := os.ReadFile(goodbyeFile.name)
	if err != nil {
	t.Fatal(err)
	}
	// Expect contents of file.
	result := string(data)
	expect := goodbyeFile.contents
	if result != expect {
	t.Fatalf("expected %q got %q", expect, result)
	}
	}

	// Test that pack-created archives can be understood by the tools.
	func TestHello(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	dir := t.TempDir()
	hello := filepath.Join(dir, "hello.go")
	prog := `
	package main
	func main() {
	println("hello world")
	}
	`
	err := os.WriteFile(hello, []byte(prog), 0666)
	if err != nil {
	t.Fatal(err)
	}

	run := func(args ...string) string {
	return doRun(t, dir, args...)
	}

	goBin := testenv.GoToolPath(t)
	run(goBin, "build", "cmd/pack") // writes pack binary to dir
	run(goBin, "tool", "compile", "hello.go")
	run("./pack", "grc", "hello.a", "hello.o")
	run(goBin, "tool", "link", "-o", "a.out", "hello.a")
	out := run("./a.out")
	if out != "hello world\n" {
	t.Fatalf("incorrect output: %q, want %q", out, "hello world\n")
	}
	}

	// Test that pack works with very long lines in PKGDEF.
	func TestLargeDefs(t *testing.T) {
	if testing.Short() {
	t.Skip("skipping in -short mode")
	}
	testenv.MustHaveGoBuild(t)

	dir := t.TempDir()
	large := filepath.Join(dir, "large.go")
	f, err := os.Create(large)
	if err != nil {
	t.Fatal(err)
	}
	b := bufio.NewWriter(f)

	printf := func(format string, args ...interface{}) {
	_, err := fmt.Fprintf(b, format, args...)
	if err != nil {
	t.Fatalf("Writing to %s: %v", large, err)
	}
	}

	printf("package large\n\ntype T struct {\n")
	for i := 0; i < 1000; i++ {
	printf("f%d int `tag:\"", i)
	for j := 0; j < 100; j++ {
	printf("t%d=%d,", j, j)
	}
	printf("\"`\n")
	}
	printf("}\n")
	if err = b.Flush(); err != nil {
	t.Fatal(err)
	}
	if err = f.Close(); err != nil {
	t.Fatal(err)
	}

	main := filepath.Join(dir, "main.go")
	prog := `
	package main
	import "large"
	var V large.T
	func main() {
	println("ok")
	}
	`
	err = os.WriteFile(main, []byte(prog), 0666)
	if err != nil {
	t.Fatal(err)
	}

	run := func(args ...string) string {
	return doRun(t, dir, args...)
	}

	goBin := testenv.GoToolPath(t)
	run(goBin, "build", "cmd/pack") // writes pack binary to dir
	run(goBin, "tool", "compile", "large.go")
	run("./pack", "grc", "large.a", "large.o")
	run(goBin, "tool", "compile", "-I", ".", "main.go")
	run(goBin, "tool", "link", "-L", ".", "-o", "a.out", "main.o")
	out := run("./a.out")
	if out != "ok\n" {
	t.Fatalf("incorrect output: %q, want %q", out, "ok\n")
	}
	}

	// Test that "\n!\n" inside export data doesn't result in a truncated
	// package definition when creating a .a archive from a .o Go object.
	func TestIssue21703(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	dir := t.TempDir()

	const aSrc = `package a; const X = "\n!\n"`
	err := os.WriteFile(filepath.Join(dir, "a.go"), []byte(aSrc), 0666)
	if err != nil {
	t.Fatal(err)
	}

	const bSrc = `package b; import _ "a"`
	err = os.WriteFile(filepath.Join(dir, "b.go"), []byte(bSrc), 0666)
	if err != nil {
	t.Fatal(err)
	}

	run := func(args ...string) string {
	return doRun(t, dir, args...)
	}

	goBin := testenv.GoToolPath(t)
	run(goBin, "build", "cmd/pack") // writes pack binary to dir
	run(goBin, "tool", "compile", "a.go")
	run("./pack", "c", "a.a", "a.o")
	run(goBin, "tool", "compile", "-I", ".", "b.go")
	}

	// Test the "c" command can "see through" the archive generated by the compiler.
	// This is peculiar. (See issue #43271)
	func TestCreateWithCompilerObj(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	dir := t.TempDir()
	src := filepath.Join(dir, "p.go")
	prog := "package p; var X = 42\n"
	err := os.WriteFile(src, []byte(prog), 0666)
	if err != nil {
	t.Fatal(err)
	}

	run := func(args ...string) string {
	return doRun(t, dir, args...)
	}

	goBin := testenv.GoToolPath(t)
	run(goBin, "build", "cmd/pack") // writes pack binary to dir
	run(goBin, "tool", "compile", "-pack", "-o", "p.a", "p.go")
	run("./pack", "c", "packed.a", "p.a")
	fi, err := os.Stat(filepath.Join(dir, "p.a"))
	if err != nil {
	t.Fatalf("stat p.a failed: %v", err)
	}
	fi2, err := os.Stat(filepath.Join(dir, "packed.a"))
	if err != nil {
	t.Fatalf("stat packed.a failed: %v", err)
	}
	// For compiler-generated object file, the "c" command is
	// expected to get (essentially) the same file back, instead
	// of packing it into a new archive with a single entry.
	if want, got := fi.Size(), fi2.Size(); want != got {
	t.Errorf("packed file with different size: want %d, got %d", want, got)
	}

	// Test -linkobj flag as well.
	run(goBin, "tool", "compile", "-linkobj", "p2.a", "-o", "p.x", "p.go")
	run("./pack", "c", "packed2.a", "p2.a")
	fi, err = os.Stat(filepath.Join(dir, "p2.a"))
	if err != nil {
	t.Fatalf("stat p2.a failed: %v", err)
	}
	fi2, err = os.Stat(filepath.Join(dir, "packed2.a"))
	if err != nil {
	t.Fatalf("stat packed2.a failed: %v", err)
	}
	if want, got := fi.Size(), fi2.Size(); want != got {
	t.Errorf("packed file with different size: want %d, got %d", want, got)
	}

	run("./pack", "c", "packed3.a", "p.x")
	fi, err = os.Stat(filepath.Join(dir, "p.x"))
	if err != nil {
	t.Fatalf("stat p.x failed: %v", err)
	}
	fi2, err = os.Stat(filepath.Join(dir, "packed3.a"))
	if err != nil {
	t.Fatalf("stat packed3.a failed: %v", err)
	}
	if want, got := fi.Size(), fi2.Size(); want != got {
	t.Errorf("packed file with different size: want %d, got %d", want, got)
	}
	}

	// Test the "r" command creates the output file if it does not exist.
	func TestRWithNonexistentFile(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	dir := t.TempDir()
	src := filepath.Join(dir, "p.go")
	prog := "package p; var X = 42\n"
	err := os.WriteFile(src, []byte(prog), 0666)
	if err != nil {
	t.Fatal(err)
	}

	run := func(args ...string) string {
	return doRun(t, dir, args...)
	}

	goBin := testenv.GoToolPath(t)
	run(goBin, "build", "cmd/pack") // writes pack binary to dir
	run(goBin, "tool", "compile", "-o", "p.o", "p.go")
	run("./pack", "r", "p.a", "p.o") // should succeed
	}

	// doRun runs a program in a directory and returns the output.
	func doRun(t *testing.T, dir string, args ...string) string {
	cmd := exec.Command(args[0], args[1:]...)
	cmd.Dir = dir
	out, err := cmd.CombinedOutput()
	if err != nil {
	t.Fatalf("%v: %v\n%s", args, err, string(out))
	}
	return string(out)
	}

	// Fake implementation of files.

	var helloFile = &FakeFile{
	name: "hello",
	contents: "hello world", // 11 bytes, an odd number.
	mode: 0644,
	}

	var goodbyeFile = &FakeFile{
	name: "goodbye",
	contents: "Sayonara, Jim", // 13 bytes, another odd number.
	mode: 0644,
	}

	// FakeFile implements FileLike and also fs.FileInfo.
	type FakeFile struct {
	name string
	contents string
	mode fs.FileMode
	offset int
	}

	// Reset prepares a FakeFile for reuse.
	func (f FakeFile) Reset() FakeFile {
	f.offset = 0
	return f
	}

	// FileLike methods.

	func (f *FakeFile) Name() string {
	// A bit of a cheat: we only have a basename, so that's also ok for FileInfo.
	return f.name
	}

	func (f *FakeFile) Stat() (fs.FileInfo, error) {
	return f, nil
	}

	func (f *FakeFile) Read(p []byte) (int, error) {
	if f.offset >= len(f.contents) {
	return 0, io.EOF
	}
	n := copy(p, f.contents[f.offset:])
	f.offset += n
	return n, nil
	}

	func (f *FakeFile) Close() error {
	return nil
	}

	// fs.FileInfo methods.

	func (f *FakeFile) Size() int64 {
	return int64(len(f.contents))
	}

	func (f *FakeFile) Mode() fs.FileMode {
	return f.mode
	}

	func (f *FakeFile) ModTime() time.Time {
	return time.Time{}
	}

	func (f *FakeFile) IsDir() bool {
	return false
	}

	func (f *FakeFile) Sys() interface{} {
	return nil
	}

	// Special helpers.

	func (f FakeFile) Entry() archive.Entry {
	return &archive.Entry{
	Name: f.name,
	Mtime: 0, // Defined to be zero.
	Uid: 0, // Ditto.
	Gid: 0, // Ditto.
	Mode: f.mode,
	Data: archive.Data{Size: int64(len(f.contents))},
	}
	}