io/ioutil: add deprecation markers to ioutil

All the code in ioutil just forwards functionality to code
in either the io or os packages, per issue 42026.

This change adds the "Deprecated" marker to all the
functions in this package.

For #42026

Fixes #51927

Change-Id: Ia807bc5c0edb06cc80ec7e35917dcfe2ad50f0ea
GitHub-Last-Rev: 3c3603f
GitHub-Pull-Request: #51961
Reviewed-on: https://go-review.googlesource.com/c/go/+/395918
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Author: jeffwidman

src/io/ioutil/ioutil.go

@@ -4,7 +4,7 @@
 
 // Package ioutil implements some I/O utility functions.
 //
-// As of Go 1.16, the same functionality is now provided
+// Deprecated: As of Go 1.16, the same functionality is now provided
 // by package io or package os, and those implementations
 // should be preferred in new code.
 // See the specific function documentation for details.
@@ -22,7 +22,7 @@ import (
 // defined to read from src until EOF, it does not treat an EOF from Read
 // as an error to be reported.
 //
-// As of Go 1.16, this function simply calls io.ReadAll.
+// Deprecated: As of Go 1.16, this function simply calls io.ReadAll.
 func ReadAll(r io.Reader) ([]byte, error) {
 	return io.ReadAll(r)
 }
@@ -32,7 +32,7 @@ func ReadAll(r io.Reader) ([]byte, error) {
 // reads the whole file, it does not treat an EOF from Read as an error
 // to be reported.
 //
-// As of Go 1.16, this function simply calls os.ReadFile.
+// Deprecated: As of Go 1.16, this function simply calls os.ReadFile.
 func ReadFile(filename string) ([]byte, error) {
 	return os.ReadFile(filename)
 }
@@ -41,7 +41,7 @@ func ReadFile(filename string) ([]byte, error) {
 // If the file does not exist, WriteFile creates it with permissions perm
 // (before umask); otherwise WriteFile truncates it before writing, without changing permissions.
 //
-// As of Go 1.16, this function simply calls os.WriteFile.
+// Deprecated: As of Go 1.16, this function simply calls os.WriteFile.
 func WriteFile(filename string, data []byte, perm fs.FileMode) error {
 	return os.WriteFile(filename, data, perm)
 }
@@ -51,7 +51,7 @@ func WriteFile(filename string, data []byte, perm fs.FileMode) error {
 // sorted by filename. If an error occurs reading the directory,
 // ReadDir returns no directory entries along with the error.
 //
-// As of Go 1.16, os.ReadDir is a more efficient and correct choice:
+// Deprecated: As of Go 1.16, os.ReadDir is a more efficient and correct choice:
 // it returns a list of fs.DirEntry instead of fs.FileInfo,
 // and it returns partial results in the case of an error
 // midway through reading a directory.
@@ -72,13 +72,13 @@ func ReadDir(dirname string) ([]fs.FileInfo, error) {
 // NopCloser returns a ReadCloser with a no-op Close method wrapping
 // the provided Reader r.
 //
-// As of Go 1.16, this function simply calls io.NopCloser.
+// Deprecated: As of Go 1.16, this function simply calls io.NopCloser.
 func NopCloser(r io.Reader) io.ReadCloser {
 	return io.NopCloser(r)
 }
 
 // Discard is an io.Writer on which all Write calls succeed
 // without doing anything.
 //
-// As of Go 1.16, this value is simply io.Discard.
+// Deprecated: As of Go 1.16, this value is simply io.Discard.
 var Discard io.Writer = io.Discard

src/io/ioutil/tempfile.go

@@ -20,7 +20,7 @@ import (
 // to find the pathname of the file. It is the caller's responsibility
 // to remove the file when no longer needed.
 //
-// As of Go 1.17, this function simply calls os.CreateTemp.
+// Deprecated: As of Go 1.17, this function simply calls os.CreateTemp.
 func TempFile(dir, pattern string) (f *os.File, err error) {
 	return os.CreateTemp(dir, pattern)
 }
@@ -35,7 +35,7 @@ func TempFile(dir, pattern string) (f *os.File, err error) {
 // will not choose the same directory. It is the caller's responsibility
 // to remove the directory when no longer needed.
 //
-// As of Go 1.17, this function simply calls os.MkdirTemp.
+// Deprecated: As of Go 1.17, this function simply calls os.MkdirTemp.
 func TempDir(dir, pattern string) (name string, err error) {
 	return os.MkdirTemp(dir, pattern)
 }