os/exec: make skipStdinCopyError a function instead of a variable

This makes clearer that skipStdinCopyError is always defined and never
overridden in tests.

Secondarily, it may also help reduce init-time work and allow the
linker and/or inliner to better optimize this package.

(Noticed while prototyping #50436.)

Change-Id: I4f3c1bc146384a98136a4039f82165ed106c14b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/401897
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/os/exec/exec.go

@@ -230,10 +230,6 @@ func (c *Cmd) argv() []string {
 	return []string{c.Path}
 }
 
-// skipStdinCopyError optionally specifies a function which reports
-// whether the provided stdin copy error should be ignored.
-var skipStdinCopyError func(error) bool
-
 func (c *Cmd) stdin() (f *os.File, err error) {
 	if c.Stdin == nil {
 		f, err = os.Open(os.DevNull)
@@ -257,7 +253,7 @@ func (c *Cmd) stdin() (f *os.File, err error) {
 	c.closeAfterWait = append(c.closeAfterWait, pw)
 	c.goroutine = append(c.goroutine, func() error {
 		_, err := io.Copy(pw, c.Stdin)
-		if skip := skipStdinCopyError; skip != nil && skip(err) {
+		if skipStdinCopyError(err) {
 			err = nil
 		}
 		if err1 := pw.Close(); err == nil {

src/os/exec/exec_plan9.go

@@ -6,14 +6,14 @@ package exec
 
 import "io/fs"
 
-func init() {
-	skipStdinCopyError = func(err error) bool {
-		// Ignore hungup errors copying to stdin if the program
-		// completed successfully otherwise.
-		// See Issue 35753.
-		pe, ok := err.(*fs.PathError)
-		return ok &&
-			pe.Op == "write" && pe.Path == "|1" &&
-			pe.Err.Error() == "i/o on hungup channel"
-	}
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore hungup errors copying to stdin if the program
+	// completed successfully otherwise.
+	// See Issue 35753.
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		pe.Err.Error() == "i/o on hungup channel"
 }

src/os/exec/exec_unix.go

@@ -11,14 +11,14 @@ import (
 	"syscall"
 )
 
-func init() {
-	skipStdinCopyError = func(err error) bool {
-		// Ignore EPIPE errors copying to stdin if the program
-		// completed successfully otherwise.
-		// See Issue 9173.
-		pe, ok := err.(*fs.PathError)
-		return ok &&
-			pe.Op == "write" && pe.Path == "|1" &&
-			pe.Err == syscall.EPIPE
-	}
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore EPIPE errors copying to stdin if the program
+	// completed successfully otherwise.
+	// See Issue 9173.
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		pe.Err == syscall.EPIPE
 }

src/os/exec/exec_windows.go

@@ -9,15 +9,15 @@ import (
 	"syscall"
 )
 
-func init() {
-	skipStdinCopyError = func(err error) bool {
-		// Ignore ERROR_BROKEN_PIPE and ERROR_NO_DATA errors copying
-		// to stdin if the program completed successfully otherwise.
-		// See Issue 20445.
-		const _ERROR_NO_DATA = syscall.Errno(0xe8)
-		pe, ok := err.(*fs.PathError)
-		return ok &&
-			pe.Op == "write" && pe.Path == "|1" &&
-			(pe.Err == syscall.ERROR_BROKEN_PIPE || pe.Err == _ERROR_NO_DATA)
-	}
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore ERROR_BROKEN_PIPE and ERROR_NO_DATA errors copying
+	// to stdin if the program completed successfully otherwise.
+	// See Issue 20445.
+	const _ERROR_NO_DATA = syscall.Errno(0xe8)
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		(pe.Err == syscall.ERROR_BROKEN_PIPE || pe.Err == _ERROR_NO_DATA)
 }