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>

1 files changed, 3 insertions, 4 deletions

diff --git a/src/strings/reader_test.go b/src/strings/reader_test.go
index a4c211d699..5adea6f7ab 100644
--- a/src/strings/reader_test.go
+++ b/src/strings/reader_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"strings"
 	"sync"
 	"testing"
@@ -162,7 +161,7 @@ func TestWriteTo(t *testing.T) {
 // tests that Len is affected by reads, but Size is not.
 func TestReaderLenSize(t *testing.T) {
 	r := strings.NewReader("abc")
-	io.CopyN(ioutil.Discard, r, 1)
+	io.CopyN(io.Discard, r, 1)
 	if r.Len() != 2 {
 		t.Errorf("Len = %d; want 2", r.Len())
 	}
@@ -182,7 +181,7 @@ func TestReaderReset(t *testing.T) {
 	if err := r.UnreadRune(); err == nil {
 		t.Errorf("UnreadRune: expected error, got nil")
 	}
-	buf, err := ioutil.ReadAll(r)
+	buf, err := io.ReadAll(r)
 	if err != nil {
 		t.Errorf("ReadAll: unexpected error: %v", err)
 	}
@@ -228,7 +227,7 @@ func TestReaderZero(t *testing.T) {
 		t.Errorf("UnreadRune: got nil, want error")
 	}
 
-	if n, err := (&strings.Reader{}).WriteTo(ioutil.Discard); n != 0 || err != nil {
+	if n, err := (&strings.Reader{}).WriteTo(io.Discard); n != 0 || err != nil {
 		t.Errorf("WriteTo: got %d, %v; want 0, nil", n, err)
 	}
 }