all: update to use os.ReadDir where appropriate

os.ReadDir is a replacement for ioutil.ReadDir that returns
a slice of fs.DirEntry instead of fs.FileInfo, meaning it is the
more efficient form.

This CL updates call sites throughout the Go source tree
wherever possible. As usual, code built using the Go 1.4
bootstrap toolchain is not included. There is also a use in
go/build that appears in the public API and can't be changed,
at least not without additional changes.

Fixes #42026.

Change-Id: Icfc9dd52c6045020f6830e22c72128499462d561
Reviewed-on: https://go-review.googlesource.com/c/go/+/266366
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

19 files changed, 91 insertions, 94 deletions

diff --git a/src/cmd/go/internal/clean/clean.go b/src/cmd/go/internal/clean/clean.go
index 87933f04f3..b1d40feb27 100644
--- a/src/cmd/go/internal/clean/clean.go
+++ b/src/cmd/go/internal/clean/clean.go
@@ -9,7 +9,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -244,7 +243,7 @@ func clean(p *load.Package) {
 		base.Errorf("%v", p.Error)
 		return
 	}
-	dirs, err := ioutil.ReadDir(p.Dir)
+	dirs, err := os.ReadDir(p.Dir)
 	if err != nil {
 		base.Errorf("go clean %s: %v", p.Dir, err)
 		return
diff --git a/src/cmd/go/internal/imports/scan_test.go b/src/cmd/go/internal/imports/scan_test.go
index 5ba3201968..2d245ee787 100644
--- a/src/cmd/go/internal/imports/scan_test.go
+++ b/src/cmd/go/internal/imports/scan_test.go
@@ -7,7 +7,6 @@ package imports
 import (
 	"bytes"
 	"internal/testenv"
-	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
@@ -58,7 +57,7 @@ func TestScan(t *testing.T) {
 func TestScanDir(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 
-	dirs, err := ioutil.ReadDir("testdata")
+	dirs, err := os.ReadDir("testdata")
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index da3e0b895c..6f95af4f7e 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -15,7 +15,6 @@ import (
 	"go/scanner"
 	"go/token"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path"
 	pathpkg "path"
@@ -1296,9 +1295,9 @@ HaveGoMod:
 // Otherwise it is not possible to vendor just a/b/c and still import the
 // non-vendored a/b. See golang.org/issue/13832.
 func hasGoFiles(dir string) bool {
-	fis, _ := ioutil.ReadDir(dir)
-	for _, fi := range fis {
-		if !fi.IsDir() && strings.HasSuffix(fi.Name(), ".go") {
+	files, _ := os.ReadDir(dir)
+	for _, f := range files {
+		if !f.IsDir() && strings.HasSuffix(f.Name(), ".go") {
 			return true
 		}
 	}
diff --git a/src/cmd/go/internal/modcmd/vendor.go b/src/cmd/go/internal/modcmd/vendor.go
index 390a195547..1bbb57d353 100644
--- a/src/cmd/go/internal/modcmd/vendor.go
+++ b/src/cmd/go/internal/modcmd/vendor.go
@@ -10,7 +10,6 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"sort"
@@ -244,7 +243,7 @@ var metaPrefixes = []string{
 }
 
 // matchMetadata reports whether info is a metadata file.
-func matchMetadata(dir string, info fs.FileInfo) bool {
+func matchMetadata(dir string, info fs.DirEntry) bool {
 	name := info.Name()
 	for _, p := range metaPrefixes {
 		if strings.HasPrefix(name, p) {
@@ -255,7 +254,7 @@ func matchMetadata(dir string, info fs.FileInfo) bool {
 }
 
 // matchPotentialSourceFile reports whether info may be relevant to a build operation.
-func matchPotentialSourceFile(dir string, info fs.FileInfo) bool {
+func matchPotentialSourceFile(dir string, info fs.DirEntry) bool {
 	if strings.HasSuffix(info.Name(), "_test.go") {
 		return false
 	}
@@ -281,8 +280,8 @@ func matchPotentialSourceFile(dir string, info fs.FileInfo) bool {
 }
 
 // copyDir copies all regular files satisfying match(info) from src to dst.
-func copyDir(dst, src string, match func(dir string, info fs.FileInfo) bool) {
-	files, err := ioutil.ReadDir(src)
+func copyDir(dst, src string, match func(dir string, info fs.DirEntry) bool) {
+	files, err := os.ReadDir(src)
 	if err != nil {
 		base.Fatalf("go mod vendor: %v", err)
 	}
@@ -290,7 +289,7 @@ func copyDir(dst, src string, match func(dir string, info fs.FileInfo) bool) {
 		base.Fatalf("go mod vendor: %v", err)
 	}
 	for _, file := range files {
-		if file.IsDir() || !file.Mode().IsRegular() || !match(src, file) {
+		if file.IsDir() || !file.Type().IsRegular() || !match(src, file) {
 			continue
 		}
 		r, err := os.Open(filepath.Join(src, file.Name()))
diff --git a/src/cmd/go/internal/modfetch/cache.go b/src/cmd/go/internal/modfetch/cache.go
index 7572ff24f8..3a2ff63721 100644
--- a/src/cmd/go/internal/modfetch/cache.go
+++ b/src/cmd/go/internal/modfetch/cache.go
@@ -11,7 +11,6 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -598,7 +597,7 @@ func rewriteVersionList(dir string) {
 	}
 	defer unlock()
 
-	infos, err := ioutil.ReadDir(dir)
+	infos, err := os.ReadDir(dir)
 	if err != nil {
 		return
 	}
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 6a2cea668d..3f70d04145 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -12,7 +12,6 @@ import (
 	"fmt"
 	"go/build"
 	"internal/lazyregexp"
-	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
@@ -445,13 +444,13 @@ func CreateModFile(ctx context.Context, modPath string) {
 	// this is an existing project. Walking the tree for packages would be more
 	// accurate, but could take much longer.
 	empty := true
-	fis, _ := ioutil.ReadDir(modRoot)
-	for _, fi := range fis {
-		name := fi.Name()
+	files, _ := os.ReadDir(modRoot)
+	for _, f := range files {
+		name := f.Name()
 		if strings.HasPrefix(name, ".") || strings.HasPrefix(name, "_") {
 			continue
 		}
-		if strings.HasSuffix(name, ".go") || fi.IsDir() {
+		if strings.HasSuffix(name, ".go") || f.IsDir() {
 			empty = false
 			break
 		}
@@ -731,9 +730,9 @@ func findModulePath(dir string) (string, error) {
 
 	// Cast about for import comments,
 	// first in top-level directory, then in subdirectories.
-	list, _ := ioutil.ReadDir(dir)
+	list, _ := os.ReadDir(dir)
 	for _, info := range list {
-		if info.Mode().IsRegular() && strings.HasSuffix(info.Name(), ".go") {
+		if info.Type().IsRegular() && strings.HasSuffix(info.Name(), ".go") {
 			if com := findImportComment(filepath.Join(dir, info.Name())); com != "" {
 				return com, nil
 			}
@@ -741,9 +740,9 @@ func findModulePath(dir string) (string, error) {
 	}
 	for _, info1 := range list {
 		if info1.IsDir() {
-			files, _ := ioutil.ReadDir(filepath.Join(dir, info1.Name()))
+			files, _ := os.ReadDir(filepath.Join(dir, info1.Name()))
 			for _, info2 := range files {
-				if info2.Mode().IsRegular() && strings.HasSuffix(info2.Name(), ".go") {
+				if info2.Type().IsRegular() && strings.HasSuffix(info2.Name(), ".go") {
 					if com := findImportComment(filepath.Join(dir, info1.Name(), info2.Name())); com != "" {
 						return path.Dir(com), nil
 					}
diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index 401b67c260..e8a7aacb85 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -13,7 +13,6 @@ import (
 	"go/build"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path"
@@ -1561,13 +1560,18 @@ func hashOpen(name string) (cache.ActionID, error) {
 	}
 	hashWriteStat(h, info)
 	if info.IsDir() {
-		names, err := ioutil.ReadDir(name)
+		files, err := os.ReadDir(name)
 		if err != nil {
 			fmt.Fprintf(h, "err %v\n", err)
 		}
-		for _, f := range names {
+		for _, f := range files {
 			fmt.Fprintf(h, "file %s ", f.Name())
-			hashWriteStat(h, f)
+			finfo, err := f.Info()
+			if err != nil {
+				fmt.Fprintf(h, "err %v\n", err)
+			} else {
+				hashWriteStat(h, finfo)
+			}
 		}
 	} else if info.Mode().IsRegular() {
 		// Because files might be very large, do not attempt
diff --git a/src/cmd/go/proxy_test.go b/src/cmd/go/proxy_test.go
index 3ed42face2..e390c73a9c 100644
--- a/src/cmd/go/proxy_test.go
+++ b/src/cmd/go/proxy_test.go
@@ -13,7 +13,6 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -75,12 +74,12 @@ func StartProxy() {
 var modList []module.Version
 
 func readModList() {
-	infos, err := ioutil.ReadDir("testdata/mod")
+	files, err := os.ReadDir("testdata/mod")
 	if err != nil {
 		log.Fatal(err)
 	}
-	for _, info := range infos {
-		name := info.Name()
+	for _, f := range files {
+		name := f.Name()
 		if !strings.HasSuffix(name, ".txt") {
 			continue
 		}
diff --git a/src/crypto/x509/root_unix.go b/src/crypto/x509/root_unix.go
index 3c643466ed..262fc079d5 100644
--- a/src/crypto/x509/root_unix.go
+++ b/src/crypto/x509/root_unix.go
@@ -8,7 +8,6 @@ package x509
 
 import (
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -82,17 +81,17 @@ func loadSystemRoots() (*CertPool, error) {
 	return nil, firstErr
 }
 
-// readUniqueDirectoryEntries is like ioutil.ReadDir but omits
+// readUniqueDirectoryEntries is like os.ReadDir but omits
 // symlinks that point within the directory.
-func readUniqueDirectoryEntries(dir string) ([]fs.FileInfo, error) {
-	fis, err := ioutil.ReadDir(dir)
+func readUniqueDirectoryEntries(dir string) ([]fs.DirEntry, error) {
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		return nil, err
 	}
-	uniq := fis[:0]
-	for _, fi := range fis {
-		if !isSameDirSymlink(fi, dir) {
-			uniq = append(uniq, fi)
+	uniq := files[:0]
+	for _, f := range files {
+		if !isSameDirSymlink(f, dir) {
+			uniq = append(uniq, f)
 		}
 	}
 	return uniq, nil
@@ -100,10 +99,10 @@ func readUniqueDirectoryEntries(dir string) ([]fs.FileInfo, error) {
 
 // isSameDirSymlink reports whether fi in dir is a symlink with a
 // target not containing a slash.
-func isSameDirSymlink(fi fs.FileInfo, dir string) bool {
-	if fi.Mode()&fs.ModeSymlink == 0 {
+func isSameDirSymlink(f fs.DirEntry, dir string) bool {
+	if f.Type()&fs.ModeSymlink == 0 {
 		return false
 	}
-	target, err := os.Readlink(filepath.Join(dir, fi.Name()))
+	target, err := os.Readlink(filepath.Join(dir, f.Name()))
 	return err == nil && !strings.Contains(target, "/")
 }
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index e9ed26aa5f..56942c0fd2 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -12,7 +12,6 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -597,7 +596,7 @@ func findImports(pkg string) ([]string, error) {
 		vpkg = "vendor/" + pkg
 	}
 	dir := filepath.Join(Default.GOROOT, "src", vpkg)
-	files, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		return nil, err
 	}
diff --git a/src/go/internal/gcimporter/gcimporter_test.go b/src/go/internal/gcimporter/gcimporter_test.go
index 8991e3bdee..3c76aafde3 100644
--- a/src/go/internal/gcimporter/gcimporter_test.go
+++ b/src/go/internal/gcimporter/gcimporter_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"fmt"
 	"internal/testenv"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -66,7 +65,7 @@ const maxTime = 30 * time.Second
 
 func testDir(t *testing.T, dir string, endTime time.Time) (nimports int) {
 	dirname := filepath.Join(runtime.GOROOT(), "pkg", runtime.GOOS+"_"+runtime.GOARCH, dir)
-	list, err := ioutil.ReadDir(dirname)
+	list, err := os.ReadDir(dirname)
 	if err != nil {
 		t.Fatalf("testDir(%s): %s", dirname, err)
 	}
@@ -144,7 +143,7 @@ func TestVersionHandling(t *testing.T) {
 	}
 
 	const dir = "./testdata/versions"
-	list, err := ioutil.ReadDir(dir)
+	list, err := os.ReadDir(dir)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/go/internal/srcimporter/srcimporter_test.go b/src/go/internal/srcimporter/srcimporter_test.go
index 102ac43f94..05b12f1636 100644
--- a/src/go/internal/srcimporter/srcimporter_test.go
+++ b/src/go/internal/srcimporter/srcimporter_test.go
@@ -10,7 +10,6 @@ import (
 	"go/token"
 	"go/types"
 	"internal/testenv"
-	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
@@ -59,7 +58,7 @@ func walkDir(t *testing.T, path string, endTime time.Time) (int, bool) {
 		return 0, false
 	}
 
-	list, err := ioutil.ReadDir(filepath.Join(runtime.GOROOT(), "src", path))
+	list, err := os.ReadDir(filepath.Join(runtime.GOROOT(), "src", path))
 	if err != nil {
 		t.Fatalf("walkDir %s failed (%v)", path, err)
 	}
diff --git a/src/go/parser/error_test.go b/src/go/parser/error_test.go
index 9b79097acf..358a844f65 100644
--- a/src/go/parser/error_test.go
+++ b/src/go/parser/error_test.go
@@ -25,7 +25,7 @@ package parser
 import (
 	"go/scanner"
 	"go/token"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
@@ -174,13 +174,13 @@ func checkErrors(t *testing.T, filename string, input interface{}) {
 }
 
 func TestErrors(t *testing.T) {
-	list, err := ioutil.ReadDir(testdata)
+	list, err := os.ReadDir(testdata)
 	if err != nil {
 		t.Fatal(err)
 	}
-	for _, fi := range list {
-		name := fi.Name()
-		if !fi.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".src") {
+	for _, d := range list {
+		name := d.Name()
+		if !d.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".src") {
 			checkErrors(t, filepath.Join(testdata, name), nil)
 		}
 	}
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
index 41d9a52847..56ff5fefb4 100644
--- a/src/go/parser/interface.go
+++ b/src/go/parser/interface.go
@@ -13,7 +13,6 @@ import (
 	"go/token"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -134,29 +133,39 @@ func ParseFile(fset *token.FileSet, filename string, src interface{}, mode Mode)
 // first error encountered are returned.
 //
 func ParseDir(fset *token.FileSet, path string, filter func(fs.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
-	list, err := ioutil.ReadDir(path)
+	list, err := os.ReadDir(path)
 	if err != nil {
 		return nil, err
 	}
 
 	pkgs = make(map[string]*ast.Package)
 	for _, d := range list {
-		if !d.IsDir() && strings.HasSuffix(d.Name(), ".go") && (filter == nil || filter(d)) {
-			filename := filepath.Join(path, d.Name())
-			if src, err := ParseFile(fset, filename, nil, mode); err == nil {
-				name := src.Name.Name
-				pkg, found := pkgs[name]
-				if !found {
-					pkg = &ast.Package{
-						Name:  name,
-						Files: make(map[string]*ast.File),
-					}
-					pkgs[name] = pkg
+		if d.IsDir() || !strings.HasSuffix(d.Name(), ".go") {
+			continue
+		}
+		if filter != nil {
+			info, err := d.Info()
+			if err != nil {
+				return nil, err
+			}
+			if !filter(info) {
+				continue
+			}
+		}
+		filename := filepath.Join(path, d.Name())
+		if src, err := ParseFile(fset, filename, nil, mode); err == nil {
+			name := src.Name.Name
+			pkg, found := pkgs[name]
+			if !found {
+				pkg = &ast.Package{
+					Name:  name,
+					Files: make(map[string]*ast.File),
 				}
-				pkg.Files[filename] = src
-			} else if first == nil {
-				first = err
+				pkgs[name] = pkg
 			}
+			pkg.Files[filename] = src
+		} else if first == nil {
+			first = err
 		}
 	}
 
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 841ca24511..ce31dab68b 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -33,7 +33,6 @@ import (
 	"go/scanner"
 	"go/token"
 	"internal/testenv"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -330,17 +329,17 @@ func TestFixedBugs(t *testing.T) { testDir(t, "fixedbugs") }
 func testDir(t *testing.T, dir string) {
 	testenv.MustHaveGoBuild(t)
 
-	fis, err := ioutil.ReadDir(dir)
+	dirs, err := os.ReadDir(dir)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	for _, fi := range fis {
-		testname := filepath.Base(fi.Name())
+	for _, d := range dirs {
+		testname := filepath.Base(d.Name())
 		testname = strings.TrimSuffix(testname, filepath.Ext(testname))
 		t.Run(testname, func(t *testing.T) {
-			filename := filepath.Join(dir, fi.Name())
-			if fi.IsDir() {
+			filename := filepath.Join(dir, d.Name())
+			if d.IsDir() {
 				t.Errorf("skipped directory %q", filename)
 				return
 			}
diff --git a/src/go/types/stdlib_test.go b/src/go/types/stdlib_test.go
index 669e7bec20..23f8f9a18d 100644
--- a/src/go/types/stdlib_test.go
+++ b/src/go/types/stdlib_test.go
@@ -16,7 +16,6 @@ import (
 	"go/scanner"
 	"go/token"
 	"internal/testenv"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -87,7 +86,7 @@ func firstComment(filename string) string {
 }
 
 func testTestDir(t *testing.T, path string, ignore ...string) {
-	files, err := ioutil.ReadDir(path)
+	files, err := os.ReadDir(path)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -297,7 +296,7 @@ func (w *walker) walk(dir string) {
 		return
 	}
 
-	fis, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		w.errh(err)
 		return
@@ -317,9 +316,9 @@ func (w *walker) walk(dir string) {
 	}
 
 	// traverse subdirectories, but don't walk into testdata
-	for _, fi := range fis {
-		if fi.IsDir() && fi.Name() != "testdata" {
-			w.walk(filepath.Join(dir, fi.Name()))
+	for _, f := range files {
+		if f.IsDir() && f.Name() != "testdata" {
+			w.walk(filepath.Join(dir, f.Name()))
 		}
 	}
 }
diff --git a/src/internal/trace/parser_test.go b/src/internal/trace/parser_test.go
index 316220cfa8..cdab95a59e 100644
--- a/src/internal/trace/parser_test.go
+++ b/src/internal/trace/parser_test.go
@@ -6,7 +6,6 @@ package trace
 
 import (
 	"bytes"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -34,19 +33,19 @@ func TestCorruptedInputs(t *testing.T) {
 }
 
 func TestParseCanned(t *testing.T) {
-	files, err := ioutil.ReadDir("./testdata")
+	files, err := os.ReadDir("./testdata")
 	if err != nil {
 		t.Fatalf("failed to read ./testdata: %v", err)
 	}
 	for _, f := range files {
-		name := filepath.Join("./testdata", f.Name())
-		info, err := os.Stat(name)
+		info, err := f.Info()
 		if err != nil {
 			t.Fatal(err)
 		}
 		if testing.Short() && info.Size() > 10000 {
 			continue
 		}
+		name := filepath.Join("./testdata", f.Name())
 		data, err := os.ReadFile(name)
 		if err != nil {
 			t.Fatal(err)
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index 92429f63a5..8b0c93f382 100644
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -15,7 +15,6 @@ import (
 	"internal/poll"
 	"internal/testenv"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -386,7 +385,7 @@ func TestPipeLookPathLeak(t *testing.T) {
 	// Reading /proc/self/fd is more reliable than calling lsof, so try that
 	// first.
 	numOpenFDs := func() (int, []byte, error) {
-		fds, err := ioutil.ReadDir("/proc/self/fd")
+		fds, err := os.ReadDir("/proc/self/fd")
 		if err != nil {
 			return 0, nil, err
 		}
diff --git a/src/testing/testing_test.go b/src/testing/testing_test.go
index d665a334e4..0f096980ca 100644
--- a/src/testing/testing_test.go
+++ b/src/testing/testing_test.go
@@ -5,7 +5,6 @@
 package testing_test
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -102,11 +101,11 @@ func testTempDir(t *testing.T) {
 	if !fi.IsDir() {
 		t.Errorf("dir %q is not a dir", dir)
 	}
-	fis, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		t.Fatal(err)
 	}
-	if len(fis) > 0 {
-		t.Errorf("unexpected %d files in TempDir: %v", len(fis), fis)
+	if len(files) > 0 {
+		t.Errorf("unexpected %d files in TempDir: %v", len(files), files)
 	}
 }