os: fix Stdin.Stat() on windows

If name is /dev/{stdin,stdout,stderr}, return fileInfo.

Fixes #14853.

Change-Id: Ibf7d1ae7b9f3dc43f6ed7c905ea2c5102e1971cc
Reviewed-on: https://go-review.googlesource.com/20845Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/os/os_test.go

@@ -1583,6 +1583,41 @@ func TestStatDirModeExec(t *testing.T) {
 	}
 }
 
+func TestStatStdin(t *testing.T) {
+	if runtime.GOOS == "plan9" {
+		t.Skipf("skipping test on plan9")
+	}
+
+	testenv.MustHaveExec(t)
+
+	if Getenv("GO_WANT_HELPER_PROCESS") == "1" {
+		st, err := Stdin.Stat()
+		if err != nil {
+			t.Fatalf("Stat failed: %v", err)
+		}
+		fmt.Println(st.Mode() & ModeNamedPipe)
+		Exit(0)
+	}
+
+	var cmd *osexec.Cmd
+	if runtime.GOOS == "windows" {
+		cmd = osexec.Command("cmd", "/c", "echo output | "+Args[0]+" -test.run=TestStatStdin")
+	} else {
+		cmd = osexec.Command("/bin/sh", "-c", "echo output | "+Args[0]+" -test.run=TestStatStdin")
+	}
+	cmd.Env = append(Environ(), "GO_WANT_HELPER_PROCESS=1")
+
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("Failed to spawn child process: %v %q", err, string(output))
+	}
+
+	// result will be like "prw-rw-rw"
+	if len(output) < 1 || output[0] != 'p' {
+		t.Fatalf("Child process reports stdin is not pipe '%v'", string(output))
+	}
+}
+
 func TestReadAtEOF(t *testing.T) {
 	f := newFile("TestReadAtEOF", t)
 	defer Remove(f.Name())

src/os/stat_windows.go

@@ -25,10 +25,19 @@ func (file *File) Stat() (FileInfo, error) {
 	if file.name == DevNull {
 		return &devNullStat, nil
 	}
+
+	ft, err := syscall.GetFileType(file.fd)
+	if err != nil {
+		return nil, &PathError{"GetFileType", file.name, err}
+	}
+	if ft == syscall.FILE_TYPE_PIPE {
+		return &fileStat{name: basename(file.name), pipe: true}, nil
+	}
+
 	var d syscall.ByHandleFileInformation
-	e := syscall.GetFileInformationByHandle(syscall.Handle(file.fd), &d)
-	if e != nil {
-		return nil, &PathError{"GetFileInformationByHandle", file.name, e}
+	err = syscall.GetFileInformationByHandle(syscall.Handle(file.fd), &d)
+	if err != nil {
+		return nil, &PathError{"GetFileInformationByHandle", file.name, err}
 	}
 	return &fileStat{
 		name: basename(file.name),
@@ -43,6 +52,7 @@ func (file *File) Stat() (FileInfo, error) {
 		vol:   d.VolumeSerialNumber,
 		idxhi: d.FileIndexHigh,
 		idxlo: d.FileIndexLow,
+		pipe:  false,
 	}, nil
 }
 

src/os/types_windows.go

@@ -14,6 +14,7 @@ import (
 type fileStat struct {
 	name string
 	sys  syscall.Win32FileAttributeData
+	pipe bool
 
 	// used to implement SameFile
 	sync.Mutex
@@ -42,6 +43,9 @@ func (fs *fileStat) Mode() (m FileMode) {
 	if fs.sys.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 {
 		m |= ModeSymlink
 	}
+	if fs.pipe {
+		m |= ModeNamedPipe
+	}
 	return m
 }