src/internal/testenv/testenv.go - go - Git at Google

 // Copyright 2015 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 testenv provides information about what functionality
 // is available in different testing environments run by the Go team.
 //
 // It is an internal package because these details are specific
 // to the Go team's test setup (on build.golang.org) and not
 // fundamental to tests in general.
 package testenv

 import (
 	"bytes"
 	"errors"
 	"flag"
 	"fmt"
 	"internal/cfg"
 	"internal/platform"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
 	"sync"
 	"testing"
 )

 // Builder reports the name of the builder running this test
 // (for example, "linux-amd64" or "windows-386-gce").
 // If the test is not running on the build infrastructure,
 // Builder returns the empty string.
 func Builder() string {
 	return os.Getenv("GO_BUILDER_NAME")
 }

 // HasGoBuild reports whether the current system can build programs with “go build”
 // and then run them with os.StartProcess or exec.Command.
 func HasGoBuild() bool {
 	if os.Getenv("GO_GCFLAGS") != "" {
 		// It's too much work to require every caller of the go command
 		// to pass along "-gcflags="+os.Getenv("GO_GCFLAGS").
 		// For now, if $GO_GCFLAGS is set, report that we simply can't
 		// run go build.
 		return false
 	}
 	switch runtime.GOOS {
 	case "android", "js", "ios":
 		return false
 	}
 	return true
 }

 // MustHaveGoBuild checks that the current system can build programs with “go build”
 // and then run them with os.StartProcess or exec.Command.
 // If not, MustHaveGoBuild calls t.Skip with an explanation.
 func MustHaveGoBuild(t testing.TB) {
 	if os.Getenv("GO_GCFLAGS") != "" {
 		t.Skipf("skipping test: 'go build' not compatible with setting $GO_GCFLAGS")
 	}
 	if !HasGoBuild() {
 		t.Skipf("skipping test: 'go build' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 }

 // HasGoRun reports whether the current system can run programs with “go run.”
 func HasGoRun() bool {
 	// For now, having go run and having go build are the same.
 	return HasGoBuild()
 }

 // MustHaveGoRun checks that the current system can run programs with “go run.”
 // If not, MustHaveGoRun calls t.Skip with an explanation.
 func MustHaveGoRun(t testing.TB) {
 	if !HasGoRun() {
 		t.Skipf("skipping test: 'go run' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 }

 // GoToolPath reports the path to the Go tool.
 // It is a convenience wrapper around GoTool.
 // If the tool is unavailable GoToolPath calls t.Skip.
 // If the tool should be available and isn't, GoToolPath calls t.Fatal.
 func GoToolPath(t testing.TB) string {
 	MustHaveGoBuild(t)
 	path, err := GoTool()
 	if err != nil {
 		t.Fatal(err)
 	}
 	// Add all environment variables that affect the Go command to test metadata.
 	// Cached test results will be invalidate when these variables change.
 	// See golang.org/issue/32285.
 	for _, envVar := range strings.Fields(cfg.KnownEnv) {
 		os.Getenv(envVar)
 	}
 	return path
 }

 var (
 	gorootOnce sync.Once
 	gorootPath string
 	gorootErr  error
 )

 func findGOROOT() (string, error) {
 	gorootOnce.Do(func() {
 		gorootPath = runtime.GOROOT()
 		if gorootPath != "" {
 			// If runtime.GOROOT() is non-empty, assume that it is valid.
 			//
 			// (It might not be: for example, the user may have explicitly set GOROOT
 			// to the wrong directory, or explicitly set GOROOT_FINAL but not GOROOT
 			// and hasn't moved the tree to GOROOT_FINAL yet. But those cases are
 			// rare, and if that happens the user can fix what they broke.)
 			return
 		}

 		// runtime.GOROOT doesn't know where GOROOT is (perhaps because the test
 		// binary was built with -trimpath, or perhaps because GOROOT_FINAL was set
 		// without GOROOT and the tree hasn't been moved there yet).
 		//
 		// Since this is internal/testenv, we can cheat and assume that the caller
 		// is a test of some package in a subdirectory of GOROOT/src. ('go test'
 		// runs the test in the directory containing the packaged under test.) That
 		// means that if we start walking up the tree, we should eventually find
 		// GOROOT/src/go.mod, and we can report the parent directory of that.

 		cwd, err := os.Getwd()
 		if err != nil {
 			gorootErr = fmt.Errorf("finding GOROOT: %w", err)
 			return
 		}

 		dir := cwd
 		for {
 			parent := filepath.Dir(dir)
 			if parent == dir {
 				// dir is either "." or only a volume name.
 				gorootErr = fmt.Errorf("failed to locate GOROOT/src in any parent directory")
 				return
 			}

 			if base := filepath.Base(dir); base != "src" {
 				dir = parent
 				continue // dir cannot be GOROOT/src if it doesn't end in "src".
 			}

 			b, err := os.ReadFile(filepath.Join(dir, "go.mod"))
 			if err != nil {
 				if os.IsNotExist(err) {
 					dir = parent
 					continue
 				}
 				gorootErr = fmt.Errorf("finding GOROOT: %w", err)
 				return
 			}
 			goMod := string(b)

 			for goMod != "" {
 				var line string
 				line, goMod, _ = strings.Cut(goMod, "\n")
 				fields := strings.Fields(line)
 				if len(fields) >= 2 && fields[0] == "module" && fields[1] == "std" {
 					// Found "module std", which is the module declaration in GOROOT/src!
 					gorootPath = parent
 					return
 				}
 			}
 		}
 	})

 	return gorootPath, gorootErr
 }

 // GOROOT reports the path to the directory containing the root of the Go
 // project source tree. This is normally equivalent to runtime.GOROOT, but
 // works even if the test binary was built with -trimpath.
 //
 // If GOROOT cannot be found, GOROOT skips t if t is non-nil,
 // or panics otherwise.
 func GOROOT(t testing.TB) string {
 	path, err := findGOROOT()
 	if err != nil {
 		if t == nil {
 			panic(err)
 		}
 		t.Helper()
 		t.Skip(err)
 	}
 	return path
 }

 // GoTool reports the path to the Go tool.
 func GoTool() (string, error) {
 	if !HasGoBuild() {
 		return "", errors.New("platform cannot run go tool")
 	}
 	var exeSuffix string
 	if runtime.GOOS == "windows" {
 		exeSuffix = ".exe"
 	}
 	goroot, err := findGOROOT()
 	if err != nil {
 		return "", fmt.Errorf("cannot find go tool: %w", err)
 	}
 	path := filepath.Join(goroot, "bin", "go"+exeSuffix)
 	if _, err := os.Stat(path); err == nil {
 		return path, nil
 	}
 	goBin, err := exec.LookPath("go" + exeSuffix)
 	if err != nil {
 		return "", errors.New("cannot find go tool: " + err.Error())
 	}
 	return goBin, nil
 }

 // HasSrc reports whether the entire source tree is available under GOROOT.
 func HasSrc() bool {
 	switch runtime.GOOS {
 	case "ios":
 		return false
 	}
 	return true
 }

 // HasExternalNetwork reports whether the current system can use
 // external (non-localhost) networks.
 func HasExternalNetwork() bool {
 	return !testing.Short() && runtime.GOOS != "js"
 }

 // MustHaveExternalNetwork checks that the current system can use
 // external (non-localhost) networks.
 // If not, MustHaveExternalNetwork calls t.Skip with an explanation.
 func MustHaveExternalNetwork(t testing.TB) {
 	if runtime.GOOS == "js" {
 		t.Skipf("skipping test: no external network on %s", runtime.GOOS)
 	}
 	if testing.Short() {
 		t.Skipf("skipping test: no external network in -short mode")
 	}
 }

 var haveCGO bool

 // HasCGO reports whether the current system can use cgo.
 func HasCGO() bool {
 	return haveCGO
 }

 // MustHaveCGO calls t.Skip if cgo is not available.
 func MustHaveCGO(t testing.TB) {
 	if !haveCGO {
 		t.Skipf("skipping test: no cgo")
 	}
 }

 // CanInternalLink reports whether the current system can link programs with
 // internal linking.
 func CanInternalLink() bool {
 	return !platform.MustLinkExternal(runtime.GOOS, runtime.GOARCH)
 }

 // MustInternalLink checks that the current system can link programs with internal
 // linking.
 // If not, MustInternalLink calls t.Skip with an explanation.
 func MustInternalLink(t testing.TB) {
 	if !CanInternalLink() {
 		t.Skipf("skipping test: internal linking on %s/%s is not supported", runtime.GOOS, runtime.GOARCH)
 	}
 }

 // HasSymlink reports whether the current system can use os.Symlink.
 func HasSymlink() bool {
 	ok, _ := hasSymlink()
 	return ok
 }

 // MustHaveSymlink reports whether the current system can use os.Symlink.
 // If not, MustHaveSymlink calls t.Skip with an explanation.
 func MustHaveSymlink(t testing.TB) {
 	ok, reason := hasSymlink()
 	if !ok {
 		t.Skipf("skipping test: cannot make symlinks on %s/%s%s", runtime.GOOS, runtime.GOARCH, reason)
 	}
 }

 // HasLink reports whether the current system can use os.Link.
 func HasLink() bool {
 	// From Android release M (Marshmallow), hard linking files is blocked
 	// and an attempt to call link() on a file will return EACCES.
 	// - https://code.google.com/p/android-developer-preview/issues/detail?id=3150
 	return runtime.GOOS != "plan9" && runtime.GOOS != "android"
 }

 // MustHaveLink reports whether the current system can use os.Link.
 // If not, MustHaveLink calls t.Skip with an explanation.
 func MustHaveLink(t testing.TB) {
 	if !HasLink() {
 		t.Skipf("skipping test: hardlinks are not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 }

 var flaky = flag.Bool("flaky", false, "run known-flaky tests too")

 func SkipFlaky(t testing.TB, issue int) {
 	t.Helper()
 	if !*flaky {
 		t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
 	}
 }

 func SkipFlakyNet(t testing.TB) {
 	t.Helper()
 	if v, _ := strconv.ParseBool(os.Getenv("GO_BUILDER_FLAKY_NET")); v {
 		t.Skip("skipping test on builder known to have frequent network failures")
 	}
 }

 // CPUIsSlow reports whether the CPU running the test is suspected to be slow.
 func CPUIsSlow() bool {
 	switch runtime.GOARCH {
 	case "arm", "mips", "mipsle", "mips64", "mips64le":
 		return true
 	}
 	return false
 }

 // SkipIfShortAndSlow skips t if -short is set and the CPU running the test is
 // suspected to be slow.
 //
 // (This is useful for CPU-intensive tests that otherwise complete quickly.)
 func SkipIfShortAndSlow(t testing.TB) {
 	if testing.Short() && CPUIsSlow() {
 		t.Helper()
 		t.Skipf("skipping test in -short mode on %s", runtime.GOARCH)
 	}
 }

 // SkipIfOptimizationOff skips t if optimization is disabled.
 func SkipIfOptimizationOff(t testing.TB) {
 	if OptimizationOff() {
 		t.Helper()
 		t.Skip("skipping test with optimization disabled")
 	}
 }

 // WriteImportcfg writes an importcfg file used by the compiler or linker to
 // dstPath containing entries for the file mappings in packageFiles, as well
 // as for the packages transitively imported by the package(s) in pkgs.
 //
 // pkgs may include any package pattern that is valid to pass to 'go list',
 // so it may also be a list of Go source files all in the same directory.
 func WriteImportcfg(t testing.TB, dstPath string, packageFiles map[string]string, pkgs ...string) {
 	t.Helper()

 	icfg := new(bytes.Buffer)
 	icfg.WriteString("# import config\n")
 	for k, v := range packageFiles {
 		fmt.Fprintf(icfg, "packagefile %s=%s\n", k, v)
 	}

 	if len(pkgs) > 0 {
 		// Use 'go list' to resolve any missing packages and rewrite the import map.
 		cmd := Command(t, GoToolPath(t), "list", "-export", "-deps", "-f", `{{if ne .ImportPath "command-line-arguments"}}{{if .Export}}{{.ImportPath}}={{.Export}}{{end}}{{end}}`)
 		cmd.Args = append(cmd.Args, pkgs...)
 		cmd.Stderr = new(strings.Builder)
 		out, err := cmd.Output()
 		if err != nil {
 			t.Fatalf("%v: %v\n%s", cmd, err, cmd.Stderr)
 		}

 		for _, line := range strings.Split(string(out), "\n") {
 			if line == "" {
 				continue
 			}
 			importPath, export, ok := strings.Cut(line, "=")
 			if !ok {
 				t.Fatalf("invalid line in output from %v:\n%s", cmd, line)
 			}
 			if packageFiles[importPath] == "" {
 				fmt.Fprintf(icfg, "packagefile %s=%s\n", importPath, export)
 			}
 		}
 	}

 	if err := os.WriteFile(dstPath, icfg.Bytes(), 0666); err != nil {
 		t.Fatal(err)
 	}
 }
	// Copyright 2015 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 testenv provides information about what functionality
	// is available in different testing environments run by the Go team.
	//
	// It is an internal package because these details are specific
	// to the Go team's test setup (on build.golang.org) and not
	// fundamental to tests in general.
	package testenv

	import (
	"bytes"
	"errors"
	"flag"
	"fmt"
	"internal/cfg"
	"internal/platform"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"testing"
	)

	// Builder reports the name of the builder running this test
	// (for example, "linux-amd64" or "windows-386-gce").
	// If the test is not running on the build infrastructure,
	// Builder returns the empty string.
	func Builder() string {
	return os.Getenv("GO_BUILDER_NAME")
	}

	// HasGoBuild reports whether the current system can build programs with “go build”
	// and then run them with os.StartProcess or exec.Command.
	func HasGoBuild() bool {
	if os.Getenv("GO_GCFLAGS") != "" {
	// It's too much work to require every caller of the go command
	// to pass along "-gcflags="+os.Getenv("GO_GCFLAGS").
	// For now, if $GO_GCFLAGS is set, report that we simply can't
	// run go build.
	return false
	}
	switch runtime.GOOS {
	case "android", "js", "ios":
	return false
	}
	return true
	}

	// MustHaveGoBuild checks that the current system can build programs with “go build”
	// and then run them with os.StartProcess or exec.Command.
	// If not, MustHaveGoBuild calls t.Skip with an explanation.
	func MustHaveGoBuild(t testing.TB) {
	if os.Getenv("GO_GCFLAGS") != "" {
	t.Skipf("skipping test: 'go build' not compatible with setting $GO_GCFLAGS")
	}
	if !HasGoBuild() {
	t.Skipf("skipping test: 'go build' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
	}
	}

	// HasGoRun reports whether the current system can run programs with “go run.”
	func HasGoRun() bool {
	// For now, having go run and having go build are the same.
	return HasGoBuild()
	}

	// MustHaveGoRun checks that the current system can run programs with “go run.”
	// If not, MustHaveGoRun calls t.Skip with an explanation.
	func MustHaveGoRun(t testing.TB) {
	if !HasGoRun() {
	t.Skipf("skipping test: 'go run' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
	}
	}

	// GoToolPath reports the path to the Go tool.
	// It is a convenience wrapper around GoTool.
	// If the tool is unavailable GoToolPath calls t.Skip.
	// If the tool should be available and isn't, GoToolPath calls t.Fatal.
	func GoToolPath(t testing.TB) string {
	MustHaveGoBuild(t)
	path, err := GoTool()
	if err != nil {
	t.Fatal(err)
	}
	// Add all environment variables that affect the Go command to test metadata.
	// Cached test results will be invalidate when these variables change.
	// See golang.org/issue/32285.
	for _, envVar := range strings.Fields(cfg.KnownEnv) {
	os.Getenv(envVar)
	}
	return path
	}

	var (
	gorootOnce sync.Once
	gorootPath string
	gorootErr error
	)

	func findGOROOT() (string, error) {
	gorootOnce.Do(func() {
	gorootPath = runtime.GOROOT()
	if gorootPath != "" {
	// If runtime.GOROOT() is non-empty, assume that it is valid.
	//
	// (It might not be: for example, the user may have explicitly set GOROOT
	// to the wrong directory, or explicitly set GOROOT_FINAL but not GOROOT
	// and hasn't moved the tree to GOROOT_FINAL yet. But those cases are
	// rare, and if that happens the user can fix what they broke.)
	return
	}

	// runtime.GOROOT doesn't know where GOROOT is (perhaps because the test
	// binary was built with -trimpath, or perhaps because GOROOT_FINAL was set
	// without GOROOT and the tree hasn't been moved there yet).
	//
	// Since this is internal/testenv, we can cheat and assume that the caller
	// is a test of some package in a subdirectory of GOROOT/src. ('go test'
	// runs the test in the directory containing the packaged under test.) That
	// means that if we start walking up the tree, we should eventually find
	// GOROOT/src/go.mod, and we can report the parent directory of that.

	cwd, err := os.Getwd()
	if err != nil {
	gorootErr = fmt.Errorf("finding GOROOT: %w", err)
	return
	}

	dir := cwd
	for {
	parent := filepath.Dir(dir)
	if parent == dir {
	// dir is either "." or only a volume name.
	gorootErr = fmt.Errorf("failed to locate GOROOT/src in any parent directory")
	return
	}

	if base := filepath.Base(dir); base != "src" {
	dir = parent
	continue // dir cannot be GOROOT/src if it doesn't end in "src".
	}

	b, err := os.ReadFile(filepath.Join(dir, "go.mod"))
	if err != nil {
	if os.IsNotExist(err) {
	dir = parent
	continue
	}
	gorootErr = fmt.Errorf("finding GOROOT: %w", err)
	return
	}
	goMod := string(b)

	for goMod != "" {
	var line string
	line, goMod, _ = strings.Cut(goMod, "\n")
	fields := strings.Fields(line)
	if len(fields) >= 2 && fields[0] == "module" && fields[1] == "std" {
	// Found "module std", which is the module declaration in GOROOT/src!
	gorootPath = parent
	return
	}
	}
	}
	})

	return gorootPath, gorootErr
	}

	// GOROOT reports the path to the directory containing the root of the Go
	// project source tree. This is normally equivalent to runtime.GOROOT, but
	// works even if the test binary was built with -trimpath.
	//
	// If GOROOT cannot be found, GOROOT skips t if t is non-nil,
	// or panics otherwise.
	func GOROOT(t testing.TB) string {
	path, err := findGOROOT()
	if err != nil {
	if t == nil {
	panic(err)
	}
	t.Helper()
	t.Skip(err)
	}
	return path
	}

	// GoTool reports the path to the Go tool.
	func GoTool() (string, error) {
	if !HasGoBuild() {
	return "", errors.New("platform cannot run go tool")
	}
	var exeSuffix string
	if runtime.GOOS == "windows" {
	exeSuffix = ".exe"
	}
	goroot, err := findGOROOT()
	if err != nil {
	return "", fmt.Errorf("cannot find go tool: %w", err)
	}
	path := filepath.Join(goroot, "bin", "go"+exeSuffix)
	if _, err := os.Stat(path); err == nil {
	return path, nil
	}
	goBin, err := exec.LookPath("go" + exeSuffix)
	if err != nil {
	return "", errors.New("cannot find go tool: " + err.Error())
	}
	return goBin, nil
	}

	// HasSrc reports whether the entire source tree is available under GOROOT.
	func HasSrc() bool {
	switch runtime.GOOS {
	case "ios":
	return false
	}
	return true
	}

	// HasExternalNetwork reports whether the current system can use
	// external (non-localhost) networks.
	func HasExternalNetwork() bool {
	return !testing.Short() && runtime.GOOS != "js"
	}

	// MustHaveExternalNetwork checks that the current system can use
	// external (non-localhost) networks.
	// If not, MustHaveExternalNetwork calls t.Skip with an explanation.
	func MustHaveExternalNetwork(t testing.TB) {
	if runtime.GOOS == "js" {
	t.Skipf("skipping test: no external network on %s", runtime.GOOS)
	}
	if testing.Short() {
	t.Skipf("skipping test: no external network in -short mode")
	}
	}

	var haveCGO bool

	// HasCGO reports whether the current system can use cgo.
	func HasCGO() bool {
	return haveCGO
	}

	// MustHaveCGO calls t.Skip if cgo is not available.
	func MustHaveCGO(t testing.TB) {
	if !haveCGO {
	t.Skipf("skipping test: no cgo")
	}
	}

	// CanInternalLink reports whether the current system can link programs with
	// internal linking.
	func CanInternalLink() bool {
	return !platform.MustLinkExternal(runtime.GOOS, runtime.GOARCH)
	}

	// MustInternalLink checks that the current system can link programs with internal
	// linking.
	// If not, MustInternalLink calls t.Skip with an explanation.
	func MustInternalLink(t testing.TB) {
	if !CanInternalLink() {
	t.Skipf("skipping test: internal linking on %s/%s is not supported", runtime.GOOS, runtime.GOARCH)
	}
	}

	// HasSymlink reports whether the current system can use os.Symlink.
	func HasSymlink() bool {
	ok, _ := hasSymlink()
	return ok
	}

	// MustHaveSymlink reports whether the current system can use os.Symlink.
	// If not, MustHaveSymlink calls t.Skip with an explanation.
	func MustHaveSymlink(t testing.TB) {
	ok, reason := hasSymlink()
	if !ok {
	t.Skipf("skipping test: cannot make symlinks on %s/%s%s", runtime.GOOS, runtime.GOARCH, reason)
	}
	}

	// HasLink reports whether the current system can use os.Link.
	func HasLink() bool {
	// From Android release M (Marshmallow), hard linking files is blocked
	// and an attempt to call link() on a file will return EACCES.
	// - https://code.google.com/p/android-developer-preview/issues/detail?id=3150
	return runtime.GOOS != "plan9" && runtime.GOOS != "android"
	}

	// MustHaveLink reports whether the current system can use os.Link.
	// If not, MustHaveLink calls t.Skip with an explanation.
	func MustHaveLink(t testing.TB) {
	if !HasLink() {
	t.Skipf("skipping test: hardlinks are not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
	}
	}

	var flaky = flag.Bool("flaky", false, "run known-flaky tests too")

	func SkipFlaky(t testing.TB, issue int) {
	t.Helper()
	if !*flaky {
	t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
	}
	}

	func SkipFlakyNet(t testing.TB) {
	t.Helper()
	if v, _ := strconv.ParseBool(os.Getenv("GO_BUILDER_FLAKY_NET")); v {
	t.Skip("skipping test on builder known to have frequent network failures")
	}
	}

	// CPUIsSlow reports whether the CPU running the test is suspected to be slow.
	func CPUIsSlow() bool {
	switch runtime.GOARCH {
	case "arm", "mips", "mipsle", "mips64", "mips64le":
	return true
	}
	return false
	}

	// SkipIfShortAndSlow skips t if -short is set and the CPU running the test is
	// suspected to be slow.
	//
	// (This is useful for CPU-intensive tests that otherwise complete quickly.)
	func SkipIfShortAndSlow(t testing.TB) {
	if testing.Short() && CPUIsSlow() {
	t.Helper()
	t.Skipf("skipping test in -short mode on %s", runtime.GOARCH)
	}
	}

	// SkipIfOptimizationOff skips t if optimization is disabled.
	func SkipIfOptimizationOff(t testing.TB) {
	if OptimizationOff() {
	t.Helper()
	t.Skip("skipping test with optimization disabled")
	}
	}

	// WriteImportcfg writes an importcfg file used by the compiler or linker to
	// dstPath containing entries for the file mappings in packageFiles, as well
	// as for the packages transitively imported by the package(s) in pkgs.
	//
	// pkgs may include any package pattern that is valid to pass to 'go list',
	// so it may also be a list of Go source files all in the same directory.
	func WriteImportcfg(t testing.TB, dstPath string, packageFiles map[string]string, pkgs ...string) {
	t.Helper()

	icfg := new(bytes.Buffer)
	icfg.WriteString("# import config\n")
	for k, v := range packageFiles {
	fmt.Fprintf(icfg, "packagefile %s=%s\n", k, v)
	}

	if len(pkgs) > 0 {
	// Use 'go list' to resolve any missing packages and rewrite the import map.
	cmd := Command(t, GoToolPath(t), "list", "-export", "-deps", "-f", `{{if ne .ImportPath "command-line-arguments"}}{{if .Export}}{{.ImportPath}}={{.Export}}{{end}}{{end}}`)
	cmd.Args = append(cmd.Args, pkgs...)
	cmd.Stderr = new(strings.Builder)
	out, err := cmd.Output()
	if err != nil {
	t.Fatalf("%v: %v\n%s", cmd, err, cmd.Stderr)
	}

	for _, line := range strings.Split(string(out), "\n") {
	if line == "" {
	continue
	}
	importPath, export, ok := strings.Cut(line, "=")
	if !ok {
	t.Fatalf("invalid line in output from %v:\n%s", cmd, line)
	}
	if packageFiles[importPath] == "" {
	fmt.Fprintf(icfg, "packagefile %s=%s\n", importPath, export)
	}
	}
	}

	if err := os.WriteFile(dstPath, icfg.Bytes(), 0666); err != nil {
	t.Fatal(err)
	}
	}