[dev.fuzz] all: merge master into dev.fuzz

Change-Id: I5d8c8329ccc9d747bd81ade6b1cb7cb8ae2e94b2

17 files changed, 141 insertions, 88 deletions

diff --git a/src/compress/bzip2/bzip2.go b/src/compress/bzip2/bzip2.go
index c40129b982..0d8c286c16 100644
--- a/src/compress/bzip2/bzip2.go
+++ b/src/compress/bzip2/bzip2.go
@@ -29,8 +29,8 @@ type reader struct {
 	setupDone    bool // true if we have parsed the bzip2 header.
 	blockSize    int  // blockSize in bytes, i.e. 900 * 1000.
 	eof          bool
-	c            [256]uint // the `C' array for the inverse BWT.
-	tt           []uint32  // mirrors the `tt' array in the bzip2 source and contains the P array in the upper 24 bits.
+	c            [256]uint // the ``C'' array for the inverse BWT.
+	tt           []uint32  // mirrors the ``tt'' array in the bzip2 source and contains the P array in the upper 24 bits.
 	tPos         uint32    // Index of the next output byte in tt.
 
 	preRLE      []uint32 // contains the RLE data still to be processed.
@@ -447,11 +447,11 @@ func (bz2 *reader) readBlock() (err error) {
 
 // inverseBWT implements the inverse Burrows-Wheeler transform as described in
 // http://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-124.pdf, section 4.2.
-// In that document, origPtr is called `I' and c is the `C' array after the
+// In that document, origPtr is called ``I'' and c is the ``C'' array after the
 // first pass over the data. It's an argument here because we merge the first
 // pass with the Huffman decoding.
 //
-// This also implements the `single array' method from the bzip2 source code
+// This also implements the ``single array'' method from the bzip2 source code
 // which leaves the output, still shuffled, in the bottom 8 bits of tt with the
 // index of the next byte in the top 24-bits. The index of the first byte is
 // returned.
diff --git a/src/compress/bzip2/bzip2_test.go b/src/compress/bzip2/bzip2_test.go
index c432bb5226..e6065cb43f 100644
--- a/src/compress/bzip2/bzip2_test.go
+++ b/src/compress/bzip2/bzip2_test.go
@@ -9,7 +9,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
-	"io/ioutil"
+	"os"
 	"testing"
 )
 
@@ -22,7 +22,7 @@ func mustDecodeHex(s string) []byte {
 }
 
 func mustLoadFile(f string) []byte {
-	b, err := ioutil.ReadFile(f)
+	b, err := os.ReadFile(f)
 	if err != nil {
 		panic(err)
 	}
@@ -133,7 +133,7 @@ func TestReader(t *testing.T) {
 
 	for i, v := range vectors {
 		rd := NewReader(bytes.NewReader(v.input))
-		buf, err := ioutil.ReadAll(rd)
+		buf, err := io.ReadAll(rd)
 
 		if fail := bool(err != nil); fail != v.fail {
 			if fail {
@@ -220,7 +220,7 @@ var (
 
 func benchmarkDecode(b *testing.B, compressed []byte) {
 	// Determine the uncompressed size of testfile.
-	uncompressedSize, err := io.Copy(ioutil.Discard, NewReader(bytes.NewReader(compressed)))
+	uncompressedSize, err := io.Copy(io.Discard, NewReader(bytes.NewReader(compressed)))
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -231,7 +231,7 @@ func benchmarkDecode(b *testing.B, compressed []byte) {
 
 	for i := 0; i < b.N; i++ {
 		r := bytes.NewReader(compressed)
-		io.Copy(ioutil.Discard, NewReader(r))
+		io.Copy(io.Discard, NewReader(r))
 	}
 }
 
diff --git a/src/compress/flate/deflate_test.go b/src/compress/flate/deflate_test.go
index 49a0345fd1..ff56712123 100644
--- a/src/compress/flate/deflate_test.go
+++ b/src/compress/flate/deflate_test.go
@@ -10,7 +10,8 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io"
-	"io/ioutil"
+	"math/rand"
+	"os"
 	"reflect"
 	"runtime/debug"
 	"sync"
@@ -156,7 +157,7 @@ func TestVeryLongSparseChunk(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping sparse chunk during short test")
 	}
-	w, err := NewWriter(ioutil.Discard, 1)
+	w, err := NewWriter(io.Discard, 1)
 	if err != nil {
 		t.Errorf("NewWriter: %v", err)
 		return
@@ -293,7 +294,7 @@ func testSync(t *testing.T, level int, input []byte, name string) {
 
 	// stream should work for ordinary reader too
 	r = NewReader(buf1)
-	out, err = ioutil.ReadAll(r)
+	out, err = io.ReadAll(r)
 	if err != nil {
 		t.Errorf("testSync: read: %s", err)
 		return
@@ -321,7 +322,7 @@ func testToFromWithLevelAndLimit(t *testing.T, level int, input []byte, name str
 		t.Logf("level: %d, size:%.2f%%, %d b\n", level, float64(buffer.Len()*100)/float64(limit), buffer.Len())
 	}
 	r := NewReader(&buffer)
-	out, err := ioutil.ReadAll(r)
+	out, err := io.ReadAll(r)
 	if err != nil {
 		t.Errorf("read: %s", err)
 		return
@@ -386,7 +387,7 @@ func TestDeflateInflateString(t *testing.T) {
 		t.Skip("skipping in short mode")
 	}
 	for _, test := range deflateInflateStringTests {
-		gold, err := ioutil.ReadFile(test.filename)
+		gold, err := os.ReadFile(test.filename)
 		if err != nil {
 			t.Error(err)
 		}
@@ -414,7 +415,7 @@ func TestReaderDict(t *testing.T) {
 	w.Close()
 
 	r := NewReaderDict(&b, []byte(dict))
-	data, err := ioutil.ReadAll(r)
+	data, err := io.ReadAll(r)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -455,7 +456,7 @@ func TestRegression2508(t *testing.T) {
 		t.Logf("test disabled with -short")
 		return
 	}
-	w, err := NewWriter(ioutil.Discard, 1)
+	w, err := NewWriter(io.Discard, 1)
 	if err != nil {
 		t.Fatalf("NewWriter: %v", err)
 	}
@@ -474,7 +475,7 @@ func TestWriterReset(t *testing.T) {
 		if testing.Short() && level > 1 {
 			break
 		}
-		w, err := NewWriter(ioutil.Discard, level)
+		w, err := NewWriter(io.Discard, level)
 		if err != nil {
 			t.Fatalf("NewWriter: %v", err)
 		}
@@ -486,9 +487,9 @@ func TestWriterReset(t *testing.T) {
 		for i := 0; i < n; i++ {
 			w.Write(buf)
 		}
-		w.Reset(ioutil.Discard)
+		w.Reset(io.Discard)
 
-		wref, err := NewWriter(ioutil.Discard, level)
+		wref, err := NewWriter(io.Discard, level)
 		if err != nil {
 			t.Fatalf("NewWriter: %v", err)
 		}
@@ -653,7 +654,7 @@ func TestBestSpeed(t *testing.T) {
 				}
 
 				r := NewReader(buf)
-				got, err := ioutil.ReadAll(r)
+				got, err := io.ReadAll(r)
 				if err != nil {
 					t.Errorf("i=%d, firstN=%d, flush=%t: ReadAll: %v", i, firstN, flush, err)
 					continue
@@ -684,7 +685,7 @@ func (w *failWriter) Write(b []byte) (int, error) {
 
 func TestWriterPersistentError(t *testing.T) {
 	t.Parallel()
-	d, err := ioutil.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+	d, err := os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
 	if err != nil {
 		t.Fatalf("ReadFile: %v", err)
 	}
@@ -880,7 +881,7 @@ func TestBestSpeedMaxMatchOffset(t *testing.T) {
 				}
 
 				r := NewReader(buf)
-				dst, err := ioutil.ReadAll(r)
+				dst, err := io.ReadAll(r)
 				r.Close()
 				if err != nil {
 					report("ReadAll: ", err)
@@ -896,6 +897,62 @@ func TestBestSpeedMaxMatchOffset(t *testing.T) {
 	}
 }
 
+func TestBestSpeedShiftOffsets(t *testing.T) {
+	// Test if shiftoffsets properly preserves matches and resets out-of-range matches
+	// seen in https://github.com/golang/go/issues/4142
+	enc := newDeflateFast()
+
+	// testData may not generate internal matches.
+	testData := make([]byte, 32)
+	rng := rand.New(rand.NewSource(0))
+	for i := range testData {
+		testData[i] = byte(rng.Uint32())
+	}
+
+	// Encode the testdata with clean state.
+	// Second part should pick up matches from the first block.
+	wantFirstTokens := len(enc.encode(nil, testData))
+	wantSecondTokens := len(enc.encode(nil, testData))
+
+	if wantFirstTokens <= wantSecondTokens {
+		t.Fatalf("test needs matches between inputs to be generated")
+	}
+	// Forward the current indicator to before wraparound.
+	enc.cur = bufferReset - int32(len(testData))
+
+	// Part 1 before wrap, should match clean state.
+	got := len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+
+	// Verify we are about to wrap.
+	if enc.cur != bufferReset {
+		t.Errorf("got %d, want e.cur to be at bufferReset (%d)", enc.cur, bufferReset)
+	}
+
+	// Part 2 should match clean state as well even if wrapped.
+	got = len(enc.encode(nil, testData))
+	if wantSecondTokens != got {
+		t.Errorf("got %d, want %d token", got, wantSecondTokens)
+	}
+
+	// Verify that we wrapped.
+	if enc.cur >= bufferReset {
+		t.Errorf("want e.cur to be < bufferReset (%d), got %d", bufferReset, enc.cur)
+	}
+
+	// Forward the current buffer, leaving the matches at the bottom.
+	enc.cur = bufferReset
+	enc.shiftOffsets()
+
+	// Ensure that no matches were picked up.
+	got = len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+}
+
 func TestMaxStackSize(t *testing.T) {
 	// This test must not run in parallel with other tests as debug.SetMaxStack
 	// affects all goroutines.
@@ -911,7 +968,7 @@ func TestMaxStackSize(t *testing.T) {
 		wg.Add(1)
 		go func(level int) {
 			defer wg.Done()
-			zw, err := NewWriter(ioutil.Discard, level)
+			zw, err := NewWriter(io.Discard, level)
 			if err != nil {
 				t.Errorf("level %d, NewWriter() = %v, want nil", level, err)
 			}
@@ -921,7 +978,7 @@ func TestMaxStackSize(t *testing.T) {
 			if err := zw.Close(); err != nil {
 				t.Errorf("level %d, Close() = %v, want nil", level, err)
 			}
-			zw.Reset(ioutil.Discard)
+			zw.Reset(io.Discard)
 		}(level)
 	}
 }
diff --git a/src/compress/flate/deflatefast.go b/src/compress/flate/deflatefast.go
index 24f8be9d5d..6aa439f13d 100644
--- a/src/compress/flate/deflatefast.go
+++ b/src/compress/flate/deflatefast.go
@@ -270,6 +270,7 @@ func (e *deflateFast) matchLen(s, t int32, src []byte) int32 {
 func (e *deflateFast) reset() {
 	e.prev = e.prev[:0]
 	// Bump the offset, so all matches will fail distance check.
+	// Nothing should be >= e.cur in the table.
 	e.cur += maxMatchOffset
 
 	// Protect against e.cur wraparound.
@@ -288,17 +289,21 @@ func (e *deflateFast) shiftOffsets() {
 		for i := range e.table[:] {
 			e.table[i] = tableEntry{}
 		}
-		e.cur = maxMatchOffset
+		e.cur = maxMatchOffset + 1
 		return
 	}
 
 	// Shift down everything in the table that isn't already too far away.
 	for i := range e.table[:] {
-		v := e.table[i].offset - e.cur + maxMatchOffset
+		v := e.table[i].offset - e.cur + maxMatchOffset + 1
 		if v < 0 {
+			// We want to reset e.cur to maxMatchOffset + 1, so we need to shift
+			// all table entries down by (e.cur - (maxMatchOffset + 1)).
+			// Because we ignore matches > maxMatchOffset, we can cap
+			// any negative offsets at 0.
 			v = 0
 		}
 		e.table[i].offset = v
 	}
-	e.cur = maxMatchOffset
+	e.cur = maxMatchOffset + 1
 }
diff --git a/src/compress/flate/dict_decoder.go b/src/compress/flate/dict_decoder.go
index 71c75a065e..3b59d48351 100644
--- a/src/compress/flate/dict_decoder.go
+++ b/src/compress/flate/dict_decoder.go
@@ -160,10 +160,8 @@ func (dd *dictDecoder) tryWriteCopy(dist, length int) int {
 	srcPos := dstPos - dist
 
 	// Copy possibly overlapping section before destination position.
-loop:
-	dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
-	if dstPos < endPos {
-		goto loop // Avoid for-loop so that this function can be inlined
+	for dstPos < endPos {
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
 	}
 
 	dd.wrPos = dstPos
diff --git a/src/compress/flate/flate_test.go b/src/compress/flate/flate_test.go
index 1e45077bd5..23f4c47b03 100644
--- a/src/compress/flate/flate_test.go
+++ b/src/compress/flate/flate_test.go
@@ -12,7 +12,6 @@ import (
 	"bytes"
 	"encoding/hex"
 	"io"
-	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -243,7 +242,7 @@ func TestStreams(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		data, err = ioutil.ReadAll(NewReader(bytes.NewReader(data)))
+		data, err = io.ReadAll(NewReader(bytes.NewReader(data)))
 		if tc.want == "fail" {
 			if err == nil {
 				t.Errorf("#%d (%s): got nil error, want non-nil", i, tc.desc)
@@ -266,7 +265,7 @@ func TestTruncatedStreams(t *testing.T) {
 
 	for i := 0; i < len(data)-1; i++ {
 		r := NewReader(strings.NewReader(data[:i]))
-		_, err := io.Copy(ioutil.Discard, r)
+		_, err := io.Copy(io.Discard, r)
 		if err != io.ErrUnexpectedEOF {
 			t.Errorf("io.Copy(%d) on truncated stream: got %v, want %v", i, err, io.ErrUnexpectedEOF)
 		}
diff --git a/src/compress/flate/huffman_bit_writer.go b/src/compress/flate/huffman_bit_writer.go
index f111f9f592..b3ae76d082 100644
--- a/src/compress/flate/huffman_bit_writer.go
+++ b/src/compress/flate/huffman_bit_writer.go
@@ -75,7 +75,8 @@ type huffmanBitWriter struct {
 	writer io.Writer
 
 	// Data waiting to be written is bytes[0:nbytes]
-	// and then the low nbits of bits.
+	// and then the low nbits of bits.  Data is always written
+	// sequentially into the bytes array.
 	bits            uint64
 	nbits           uint
 	bytes           [bufferSize]byte
@@ -105,7 +106,6 @@ func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
 func (w *huffmanBitWriter) reset(writer io.Writer) {
 	w.writer = writer
 	w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
-	w.bytes = [bufferSize]byte{}
 }
 
 func (w *huffmanBitWriter) flush() {
diff --git a/src/compress/flate/huffman_bit_writer_test.go b/src/compress/flate/huffman_bit_writer_test.go
index 882d3abec1..a57799cae0 100644
--- a/src/compress/flate/huffman_bit_writer_test.go
+++ b/src/compress/flate/huffman_bit_writer_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -38,7 +37,7 @@ func TestBlockHuff(t *testing.T) {
 }
 
 func testBlockHuff(t *testing.T, in, out string) {
-	all, err := ioutil.ReadFile(in)
+	all, err := os.ReadFile(in)
 	if err != nil {
 		t.Error(err)
 		return
@@ -49,7 +48,7 @@ func testBlockHuff(t *testing.T, in, out string) {
 	bw.flush()
 	got := buf.Bytes()
 
-	want, err := ioutil.ReadFile(out)
+	want, err := os.ReadFile(out)
 	if err != nil && !*update {
 		t.Error(err)
 		return
@@ -60,7 +59,7 @@ func testBlockHuff(t *testing.T, in, out string) {
 		if *update {
 			if in != out {
 				t.Logf("Updating %q", out)
-				if err := ioutil.WriteFile(out, got, 0666); err != nil {
+				if err := os.WriteFile(out, got, 0666); err != nil {
 					t.Error(err)
 				}
 				return
@@ -70,7 +69,7 @@ func testBlockHuff(t *testing.T, in, out string) {
 		}
 
 		t.Errorf("%q != %q (see %q)", in, out, in+".got")
-		if err := ioutil.WriteFile(in+".got", got, 0666); err != nil {
+		if err := os.WriteFile(in+".got", got, 0666); err != nil {
 			t.Error(err)
 		}
 		return
@@ -85,7 +84,7 @@ func testBlockHuff(t *testing.T, in, out string) {
 	got = buf.Bytes()
 	if !bytes.Equal(got, want) {
 		t.Errorf("after reset %q != %q (see %q)", in, out, in+".reset.got")
-		if err := ioutil.WriteFile(in+".reset.got", got, 0666); err != nil {
+		if err := os.WriteFile(in+".reset.got", got, 0666); err != nil {
 			t.Error(err)
 		}
 		return
@@ -186,7 +185,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 	if *update {
 		if test.input != "" {
 			t.Logf("Updating %q", test.want)
-			input, err := ioutil.ReadFile(test.input)
+			input, err := os.ReadFile(test.input)
 			if err != nil {
 				t.Error(err)
 				return
@@ -216,12 +215,12 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 
 	if test.input != "" {
 		t.Logf("Testing %q", test.want)
-		input, err := ioutil.ReadFile(test.input)
+		input, err := os.ReadFile(test.input)
 		if err != nil {
 			t.Error(err)
 			return
 		}
-		want, err := ioutil.ReadFile(test.want)
+		want, err := os.ReadFile(test.want)
 		if err != nil {
 			t.Error(err)
 			return
@@ -233,7 +232,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 		got := buf.Bytes()
 		if !bytes.Equal(got, want) {
 			t.Errorf("writeBlock did not yield expected result for file %q with input. See %q", test.want, test.want+".got")
-			if err := ioutil.WriteFile(test.want+".got", got, 0666); err != nil {
+			if err := os.WriteFile(test.want+".got", got, 0666); err != nil {
 				t.Error(err)
 			}
 		}
@@ -247,7 +246,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 		got = buf.Bytes()
 		if !bytes.Equal(got, want) {
 			t.Errorf("reset: writeBlock did not yield expected result for file %q with input. See %q", test.want, test.want+".reset.got")
-			if err := ioutil.WriteFile(test.want+".reset.got", got, 0666); err != nil {
+			if err := os.WriteFile(test.want+".reset.got", got, 0666); err != nil {
 				t.Error(err)
 			}
 			return
@@ -256,7 +255,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 		testWriterEOF(t, "wb", test, true)
 	}
 	t.Logf("Testing %q", test.wantNoInput)
-	wantNI, err := ioutil.ReadFile(test.wantNoInput)
+	wantNI, err := os.ReadFile(test.wantNoInput)
 	if err != nil {
 		t.Error(err)
 		return
@@ -268,7 +267,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 	got := buf.Bytes()
 	if !bytes.Equal(got, wantNI) {
 		t.Errorf("writeBlock did not yield expected result for file %q with input. See %q", test.wantNoInput, test.wantNoInput+".got")
-		if err := ioutil.WriteFile(test.want+".got", got, 0666); err != nil {
+		if err := os.WriteFile(test.want+".got", got, 0666); err != nil {
 			t.Error(err)
 		}
 	} else if got[0]&1 == 1 {
@@ -286,7 +285,7 @@ func testBlock(t *testing.T, test huffTest, ttype string) {
 	got = buf.Bytes()
 	if !bytes.Equal(got, wantNI) {
 		t.Errorf("reset: writeBlock did not yield expected result for file %q without input. See %q", test.want, test.want+".reset.got")
-		if err := ioutil.WriteFile(test.want+".reset.got", got, 0666); err != nil {
+		if err := os.WriteFile(test.want+".reset.got", got, 0666); err != nil {
 			t.Error(err)
 		}
 		return
@@ -325,7 +324,7 @@ func testWriterEOF(t *testing.T, ttype string, test huffTest, useInput bool) {
 	var input []byte
 	if useInput {
 		var err error
-		input, err = ioutil.ReadFile(test.input)
+		input, err = os.ReadFile(test.input)
 		if err != nil {
 			t.Error(err)
 			return
diff --git a/src/compress/flate/inflate_test.go b/src/compress/flate/inflate_test.go
index 951decd775..9575be1cf2 100644
--- a/src/compress/flate/inflate_test.go
+++ b/src/compress/flate/inflate_test.go
@@ -7,7 +7,6 @@ package flate
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -57,7 +56,7 @@ func TestReaderTruncated(t *testing.T) {
 	for i, v := range vectors {
 		r := strings.NewReader(v.input)
 		zr := NewReader(r)
-		b, err := ioutil.ReadAll(zr)
+		b, err := io.ReadAll(zr)
 		if err != io.ErrUnexpectedEOF {
 			t.Errorf("test %d, error mismatch: got %v, want io.ErrUnexpectedEOF", i, err)
 		}
diff --git a/src/compress/flate/reader_test.go b/src/compress/flate/reader_test.go
index 9d2943a540..94610fbb78 100644
--- a/src/compress/flate/reader_test.go
+++ b/src/compress/flate/reader_test.go
@@ -7,7 +7,7 @@ package flate
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
+	"os"
 	"runtime"
 	"strings"
 	"testing"
@@ -16,7 +16,7 @@ import (
 func TestNlitOutOfRange(t *testing.T) {
 	// Trying to decode this bogus flate data, which has a Huffman table
 	// with nlit=288, should not panic.
-	io.Copy(ioutil.Discard, NewReader(strings.NewReader(
+	io.Copy(io.Discard, NewReader(strings.NewReader(
 		"\xfc\xfe\x36\xe7\x5e\x1c\xef\xb3\x55\x58\x77\xb6\x56\xb5\x43\xf4"+
 			"\x6f\xf2\xd2\xe6\x3d\x99\xa0\x85\x8c\x48\xeb\xf8\xda\x83\x04\x2a"+
 			"\x75\xc4\xf8\x0f\x12\x11\xb9\xb4\x4b\x09\xa0\xbe\x8b\x91\x4c")))
@@ -54,7 +54,7 @@ func BenchmarkDecode(b *testing.B) {
 		runtime.GC()
 		b.StartTimer()
 		for i := 0; i < b.N; i++ {
-			io.Copy(ioutil.Discard, NewReader(bytes.NewReader(buf1)))
+			io.Copy(io.Discard, NewReader(bytes.NewReader(buf1)))
 		}
 	})
 }
@@ -80,7 +80,7 @@ var sizes = []struct {
 
 func doBench(b *testing.B, f func(b *testing.B, buf []byte, level, n int)) {
 	for _, suite := range suites {
-		buf, err := ioutil.ReadFile(suite.file)
+		buf, err := os.ReadFile(suite.file)
 		if err != nil {
 			b.Fatal(err)
 		}
diff --git a/src/compress/flate/writer_test.go b/src/compress/flate/writer_test.go
index 881cb71cc3..c413735cd2 100644
--- a/src/compress/flate/writer_test.go
+++ b/src/compress/flate/writer_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math/rand"
 	"runtime"
 	"testing"
@@ -27,14 +26,14 @@ func BenchmarkEncode(b *testing.B) {
 			copy(buf1[i:], buf0)
 		}
 		buf0 = nil
-		w, err := NewWriter(ioutil.Discard, level)
+		w, err := NewWriter(io.Discard, level)
 		if err != nil {
 			b.Fatal(err)
 		}
 		runtime.GC()
 		b.StartTimer()
 		for i := 0; i < b.N; i++ {
-			w.Reset(ioutil.Discard)
+			w.Reset(io.Discard)
 			w.Write(buf1)
 			w.Close()
 		}
@@ -96,7 +95,7 @@ func TestWriteError(t *testing.T) {
 				t.Fatal("Level", l, "Expected an error on close")
 			}
 
-			w.Reset(ioutil.Discard)
+			w.Reset(io.Discard)
 			n2, err = w.Write([]byte{1, 2, 3, 4, 5, 6})
 			if err != nil {
 				t.Fatal("Level", l, "Got unexpected error after reset:", err)
@@ -206,7 +205,7 @@ func TestDeflateFast_Reset(t *testing.T) {
 	w.Close()
 
 	for ; offset <= 256; offset *= 2 {
-		w, err := NewWriter(ioutil.Discard, level)
+		w, err := NewWriter(io.Discard, level)
 		if err != nil {
 			t.Fatalf("NewWriter: level %d: %v", level, err)
 		}
diff --git a/src/compress/gzip/gunzip_test.go b/src/compress/gzip/gunzip_test.go
index 1b01404169..17c23e8a9b 100644
--- a/src/compress/gzip/gunzip_test.go
+++ b/src/compress/gzip/gunzip_test.go
@@ -9,7 +9,6 @@ import (
 	"compress/flate"
 	"encoding/base64"
 	"io"
-	"io/ioutil"
 	"os"
 	"strings"
 	"testing"
@@ -430,7 +429,7 @@ func TestIssue6550(t *testing.T) {
 	defer gzip.Close()
 	done := make(chan bool, 1)
 	go func() {
-		_, err := io.Copy(ioutil.Discard, gzip)
+		_, err := io.Copy(io.Discard, gzip)
 		if err == nil {
 			t.Errorf("Copy succeeded")
 		} else {
@@ -467,7 +466,7 @@ Found:
 	const hello = "hello world\n"
 
 	r.Multistream(false)
-	data, err := ioutil.ReadAll(&r)
+	data, err := io.ReadAll(&r)
 	if string(data) != hello || err != nil {
 		t.Fatalf("first stream = %q, %v, want %q, %v", string(data), err, hello, nil)
 	}
@@ -476,7 +475,7 @@ Found:
 		t.Fatalf("second reset: %v", err)
 	}
 	r.Multistream(false)
-	data, err = ioutil.ReadAll(&r)
+	data, err = io.ReadAll(&r)
 	if string(data) != hello || err != nil {
 		t.Fatalf("second stream = %q, %v, want %q, %v", string(data), err, hello, nil)
 	}
@@ -507,7 +506,7 @@ func TestTruncatedStreams(t *testing.T) {
 			}
 			continue
 		}
-		_, err = io.Copy(ioutil.Discard, r)
+		_, err = io.Copy(io.Discard, r)
 		if ferr, ok := err.(*flate.ReadError); ok {
 			err = ferr.Err
 		}
diff --git a/src/compress/gzip/gzip_test.go b/src/compress/gzip/gzip_test.go
index f18c5cb454..12c8e18207 100644
--- a/src/compress/gzip/gzip_test.go
+++ b/src/compress/gzip/gzip_test.go
@@ -8,7 +8,6 @@ import (
 	"bufio"
 	"bytes"
 	"io"
-	"io/ioutil"
 	"reflect"
 	"testing"
 	"time"
@@ -29,7 +28,7 @@ func TestEmpty(t *testing.T) {
 	if want := (Header{OS: 255}); !reflect.DeepEqual(r.Header, want) {
 		t.Errorf("Header mismatch:\ngot  %#v\nwant %#v", r.Header, want)
 	}
-	b, err := ioutil.ReadAll(r)
+	b, err := io.ReadAll(r)
 	if err != nil {
 		t.Fatalf("ReadAll: %v", err)
 	}
@@ -62,7 +61,7 @@ func TestRoundTrip(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewReader: %v", err)
 	}
-	b, err := ioutil.ReadAll(r)
+	b, err := io.ReadAll(r)
 	if err != nil {
 		t.Fatalf("ReadAll: %v", err)
 	}
@@ -147,7 +146,7 @@ func TestLatin1RoundTrip(t *testing.T) {
 			t.Errorf("NewReader: %v", err)
 			continue
 		}
-		_, err = ioutil.ReadAll(r)
+		_, err = io.ReadAll(r)
 		if err != nil {
 			t.Errorf("ReadAll: %v", err)
 			continue
@@ -217,7 +216,7 @@ func TestConcat(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	data, err := ioutil.ReadAll(r)
+	data, err := io.ReadAll(r)
 	if string(data) != "hello world\n" || err != nil {
 		t.Fatalf("ReadAll = %q, %v, want %q, nil", data, err, "hello world")
 	}
diff --git a/src/compress/gzip/issue14937_test.go b/src/compress/gzip/issue14937_test.go
index 7a19672d57..20da0b6824 100644
--- a/src/compress/gzip/issue14937_test.go
+++ b/src/compress/gzip/issue14937_test.go
@@ -2,6 +2,7 @@ package gzip
 
 import (
 	"internal/testenv"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -30,7 +31,7 @@ func TestGZIPFilesHaveZeroMTimes(t *testing.T) {
 		t.Fatal("error evaluating GOROOT: ", err)
 	}
 	var files []string
-	err = filepath.Walk(goroot, func(path string, info os.FileInfo, err error) error {
+	err = filepath.WalkDir(goroot, func(path string, info fs.DirEntry, err error) error {
 		if err != nil {
 			return err
 		}
diff --git a/src/compress/lzw/reader_test.go b/src/compress/lzw/reader_test.go
index 98bbfbb763..d1eb76d042 100644
--- a/src/compress/lzw/reader_test.go
+++ b/src/compress/lzw/reader_test.go
@@ -8,8 +8,8 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
+	"os"
 	"runtime"
 	"strconv"
 	"strings"
@@ -206,7 +206,7 @@ func TestNoLongerSavingPriorExpansions(t *testing.T) {
 	in = append(in, 0x80, 0xff, 0x0f, 0x08)
 
 	r := NewReader(bytes.NewReader(in), LSB, 8)
-	nDecoded, err := io.Copy(ioutil.Discard, r)
+	nDecoded, err := io.Copy(io.Discard, r)
 	if err != nil {
 		t.Fatalf("Copy: %v", err)
 	}
@@ -218,7 +218,7 @@ func TestNoLongerSavingPriorExpansions(t *testing.T) {
 }
 
 func BenchmarkDecoder(b *testing.B) {
-	buf, err := ioutil.ReadFile("../testdata/e.txt")
+	buf, err := os.ReadFile("../testdata/e.txt")
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -246,7 +246,7 @@ func BenchmarkDecoder(b *testing.B) {
 			runtime.GC()
 			b.StartTimer()
 			for i := 0; i < b.N; i++ {
-				io.Copy(ioutil.Discard, NewReader(bytes.NewReader(buf1), LSB, 8))
+				io.Copy(io.Discard, NewReader(bytes.NewReader(buf1), LSB, 8))
 			}
 		})
 	}
diff --git a/src/compress/lzw/writer_test.go b/src/compress/lzw/writer_test.go
index 4979f8b352..1a5dbcae93 100644
--- a/src/compress/lzw/writer_test.go
+++ b/src/compress/lzw/writer_test.go
@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io"
-	"io/ioutil"
 	"math"
 	"os"
 	"runtime"
@@ -67,8 +66,8 @@ func testFile(t *testing.T, fn string, order Order, litWidth int) {
 	defer lzwr.Close()
 
 	// Compare the two.
-	b0, err0 := ioutil.ReadAll(golden)
-	b1, err1 := ioutil.ReadAll(lzwr)
+	b0, err0 := io.ReadAll(golden)
+	b1, err1 := io.ReadAll(lzwr)
 	if err0 != nil {
 		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err0)
 		return
@@ -107,7 +106,7 @@ func TestWriter(t *testing.T) {
 }
 
 func TestWriterReturnValues(t *testing.T) {
-	w := NewWriter(ioutil.Discard, LSB, 8)
+	w := NewWriter(io.Discard, LSB, 8)
 	n, err := w.Write([]byte("asdf"))
 	if n != 4 || err != nil {
 		t.Errorf("got %d, %v, want 4, nil", n, err)
@@ -115,7 +114,7 @@ func TestWriterReturnValues(t *testing.T) {
 }
 
 func TestSmallLitWidth(t *testing.T) {
-	w := NewWriter(ioutil.Discard, LSB, 2)
+	w := NewWriter(io.Discard, LSB, 2)
 	if _, err := w.Write([]byte{0x03}); err != nil {
 		t.Fatalf("write a byte < 1<<2: %v", err)
 	}
@@ -125,7 +124,7 @@ func TestSmallLitWidth(t *testing.T) {
 }
 
 func BenchmarkEncoder(b *testing.B) {
-	buf, err := ioutil.ReadFile("../testdata/e.txt")
+	buf, err := os.ReadFile("../testdata/e.txt")
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -148,7 +147,7 @@ func BenchmarkEncoder(b *testing.B) {
 		b.Run(fmt.Sprint("1e", e), func(b *testing.B) {
 			b.SetBytes(int64(n))
 			for i := 0; i < b.N; i++ {
-				w := NewWriter(ioutil.Discard, LSB, 8)
+				w := NewWriter(io.Discard, LSB, 8)
 				w.Write(buf1)
 				w.Close()
 			}
diff --git a/src/compress/zlib/writer_test.go b/src/compress/zlib/writer_test.go
index d501974078..f0b38880a6 100644
--- a/src/compress/zlib/writer_test.go
+++ b/src/compress/zlib/writer_test.go
@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io"
-	"io/ioutil"
 	"os"
 	"testing"
 )
@@ -34,7 +33,7 @@ func testFileLevelDict(t *testing.T, fn string, level int, d string) {
 		return
 	}
 	defer golden.Close()
-	b0, err0 := ioutil.ReadAll(golden)
+	b0, err0 := io.ReadAll(golden)
 	if err0 != nil {
 		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err0)
 		return
@@ -74,7 +73,7 @@ func testLevelDict(t *testing.T, fn string, b0 []byte, level int, d string) {
 	defer zlibr.Close()
 
 	// Compare the decompressed data.
-	b1, err1 := ioutil.ReadAll(zlibr)
+	b1, err1 := io.ReadAll(zlibr)
 	if err1 != nil {
 		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err1)
 		return
@@ -95,7 +94,7 @@ func testFileLevelDictReset(t *testing.T, fn string, level int, dict []byte) {
 	var b0 []byte
 	var err error
 	if fn != "" {
-		b0, err = ioutil.ReadFile(fn)
+		b0, err = os.ReadFile(fn)
 		if err != nil {
 			t.Errorf("%s (level=%d): %v", fn, level, err)
 			return