os, syscall: permit setting mtime to Unix 0 on Windows

This edge case was accidentally broken by CL 219638.

Change-Id: I673b3b580fbe379a04f8650cf5969fe9bce83691
Reviewed-on: https://go-review.googlesource.com/c/go/+/495036
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

3 files changed, 33 insertions, 3 deletions

diff --git a/src/os/file_windows.go b/src/os/file_windows.go
index 37db3f931c..c77d182fae 100644
--- a/src/os/file_windows.go
+++ b/src/os/file_windows.go
@@ -14,7 +14,8 @@ import (
 	"unsafe"
 )
 
-const _UTIME_OMIT = 0
+// This matches the value in syscall/syscall_windows.go.
+const _UTIME_OMIT = -1
 
 // file is the real representation of *File.
 // The extra level of indirection ensures that no clients of os
diff --git a/src/os/os_test.go b/src/os/os_test.go
index 3f4fbabb2d..09d923a338 100644
--- a/src/os/os_test.go
+++ b/src/os/os_test.go
@@ -1568,6 +1568,32 @@ func testChtimes(t *testing.T, name string) {
 	}
 }
 
+func TestChtimesToUnixZero(t *testing.T) {
+	file := newFile("chtimes-to-unix-zero", t)
+	fn := file.Name()
+	defer Remove(fn)
+	if _, err := file.Write([]byte("hi")); err != nil {
+		t.Fatal(err)
+	}
+	if err := file.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	unixZero := time.Unix(0, 0)
+	if err := Chtimes(fn, unixZero, unixZero); err != nil {
+		t.Fatalf("Chtimes failed: %v", err)
+	}
+
+	st, err := Stat(fn)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if mt := st.ModTime(); mt != unixZero {
+		t.Errorf("mtime is %v, want %v", mt, unixZero)
+	}
+}
+
 func TestFileChdir(t *testing.T) {
 	wd, err := Getwd()
 	if err != nil {
diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index c3fa415832..d721309781 100644
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -658,6 +658,9 @@ func Utimes(path string, tv []Timeval) (err error) {
 	return SetFileTime(h, nil, &a, &w)
 }
 
+// This matches the value in os/file_windows.go.
+const _UTIME_OMIT = -1
+
 func UtimesNano(path string, ts []Timespec) (err error) {
 	if len(ts) != 2 {
 		return EINVAL
@@ -675,10 +678,10 @@ func UtimesNano(path string, ts []Timespec) (err error) {
 	defer Close(h)
 	a := Filetime{}
 	w := Filetime{}
-	if TimespecToNsec(ts[0]) != 0 {
+	if ts[0].Nsec != _UTIME_OMIT {
 		a = NsecToFiletime(TimespecToNsec(ts[0]))
 	}
-	if TimespecToNsec(ts[1]) != 0 {
+	if ts[1].Nsec != _UTIME_OMIT {
 		w = NsecToFiletime(TimespecToNsec(ts[1]))
 	}
 	return SetFileTime(h, nil, &a, &w)