all: update references to symbols moved from io/ioutil to io

The old ioutil references are still valid, but update our code
to reflect best practices and get used to the new locations.

Code compiled with the bootstrap toolchain
(cmd/asm, cmd/dist, cmd/compile, debug/elf)
must remain Go 1.4-compatible and is excluded.
Also excluded vendored code.

For #41190.

Change-Id: I6d86f2bf7bc37a9d904b6cee3fe0c7af6d94d5b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/263142
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

11 files changed, 41 insertions, 46 deletions

diff --git a/src/compress/bzip2/bzip2_test.go b/src/compress/bzip2/bzip2_test.go
index c432bb5226..98477791b3 100644
--- a/src/compress/bzip2/bzip2_test.go
+++ b/src/compress/bzip2/bzip2_test.go
@@ -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 b19cbec5a9..6fc5abf4d5 100644
--- a/src/compress/flate/deflate_test.go
+++ b/src/compress/flate/deflate_test.go
@@ -157,7 +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
@@ -294,7 +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
@@ -322,7 +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
@@ -415,7 +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)
 	}
@@ -456,7 +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)
 	}
@@ -475,7 +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)
 		}
@@ -487,9 +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)
 		}
@@ -654,7 +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
@@ -881,7 +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)
@@ -968,7 +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)
 			}
@@ -978,7 +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/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/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..eb32c89184 100644
--- a/src/compress/flate/reader_test.go
+++ b/src/compress/flate/reader_test.go
@@ -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)))
 		}
 	})
 }
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/lzw/reader_test.go b/src/compress/lzw/reader_test.go
index 98bbfbb763..6d91dd806f 100644
--- a/src/compress/lzw/reader_test.go
+++ b/src/compress/lzw/reader_test.go
@@ -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)
 	}
@@ -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..33a28bdd3a 100644
--- a/src/compress/lzw/writer_test.go
+++ b/src/compress/lzw/writer_test.go
@@ -67,8 +67,8 @@ 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 +107,7 @@ 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 +115,7 @@ 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)
 	}
@@ -148,7 +148,7 @@ 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..c518729146 100644
--- a/src/compress/zlib/writer_test.go
+++ b/src/compress/zlib/writer_test.go
@@ -34,7 +34,7 @@ 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 +74,7 @@ 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