proposal: os: support deleting files with POSIX semantics for Windows 2019 and older

[stanhu]

Proposal Details

os.Remove on Windows uses syscall.DeleteFile, which cannot delete files that are currently open.

In Go 1.26 (https://go-review.googlesource.com/c/go/+/713480, b31dc77) os.RemoveAll attempts to use FILE_DISPOSITION_POSIX_SEMANTICS for Windows if available.

I propose we do something similar for os.Remove to make this consistent:

diff --git a/src/internal/syscall/windows/at_windows.go b/src/internal/syscall/windows/at_windows.go
index f654e036ac..7020ee2766 100644
--- a/src/internal/syscall/windows/at_windows.go
+++ b/src/internal/syscall/windows/at_windows.go
@@ -319,6 +319,53 @@ func deleteatFallback(h syscall.Handle) error {
 	)
 }
 
+func RemoveEx(path string) (fallback bool, err error) {
+	// Attempt to remove the file using POSIX semantics
+	// (which permit a file to be deleted while it is still open).
+	objAttrs := &OBJECT_ATTRIBUTES{}
+	if err := objAttrs.init(syscall.InvalidHandle, path); err != nil {
+		return true, err
+	}
+	var h syscall.Handle
+	err = NtOpenFile(
+		&h,
+		DELETE,
+		objAttrs,
+		&IO_STATUS_BLOCK{},
+		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
+		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT,
+	)
+	if err != nil {
+		return true, err
+	}
+	defer syscall.CloseHandle(h)
+
+	const FileDispositionInformationEx = 64
+
+	err = NtSetInformationFile(
+		h,
+		&IO_STATUS_BLOCK{},
+		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION_EX{
+			Flags: FILE_DISPOSITION_DELETE |
+				FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK |
+				FILE_DISPOSITION_POSIX_SEMANTICS |
+				FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE,
+		}),
+		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION_EX{})),
+		FileDispositionInformationEx,
+	)
+	switch err {
+	case nil:
+		return false, nil
+	case STATUS_INVALID_INFO_CLASS,
+		STATUS_INVALID_PARAMETER,
+		STATUS_NOT_SUPPORTED:
+		return true, nil
+	default:
+		return false, err
+	}
+}
+
 func Renameat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
 	objAttrs := &OBJECT_ATTRIBUTES{}
 	if err := objAttrs.init(olddirfd, oldpath); err != nil {
diff --git a/src/os/file_windows.go b/src/os/file_windows.go
index ad172b5048..4480c7d8d3 100644
--- a/src/os/file_windows.go
+++ b/src/os/file_windows.go
@@ -220,6 +220,15 @@ func Truncate(name string, size int64) error {
 // Remove removes the named file or directory.
 // If there is an error, it will be of type [*PathError].
 func Remove(name string) error {
+	// First try using POSIX semantics (allows deleting while open).
+	// This matches the behavior of Deleteat and os.Remove on Unix.
+	if fallback, err := windows.RemoveEx(name); err == nil {
+		return nil
+	} else if !fallback {
+		return &PathError{Op: "remove", Path: name, Err: err}
+	}
+
+	// Fall back to traditional DeleteFile/RemoveDirectory.
 	p, e := syscall.UTF16PtrFromString(fixLongPath(name))
 	if e != nil {
 		return &PathError{Op: "remove", Path: name, Err: e}

[gabyhelp]

Related Issues

• proposal: os: Create/Open/OpenFile() set FILE_SHARE_DELETE on windows #32088 (closed)
• os: Remove/RemoveAll should remove read-only files on Windows #9606 (closed)
• os: on windows RemoveAll removing directories containing read-only files errors with `unlinkat ... Access is denied` #75922 (closed)
• os: Go 1.25.x regression on RemoveAll for windows #77402 (closed)
• proposal: syscall: define Windows O_ALLOW_DELETE for use in os.OpenFile #34681 (closed)
• os: on windows RemoveAll removing directories containing read-only files errors with `unlinkat ... Access is denied`, ReOpenFile error handling followup [1.25 backport] #76360 (closed)

Related Code Changes

• os: support deleting read-only files in RemoveAll on older Windows versions
• os: fix Remove for file with read only attribute on Windows
• misc/makerelease: use built in "del" to remove files
• os: support deleting inaccessible files in RemoveAll

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

what does older windows versions mean?

cc @golang/windows

[qmuntal]

The issue title mentions removing read-only files, but those are already supported by os.Remove:

go/src/os/file_windows.go

Lines 247 to 254 in e30e65f

	} else if a&syscall.FILE_ATTRIBUTE_READONLY != 0 {
	if e1 = syscall.SetFileAttributes(p, a&^syscall.FILE_ATTRIBUTE_READONLY); e1 == nil {
	if e = syscall.DeleteFile(p); e == nil {
	return nil
	}
	}
	}
	}

The issue description, in the other hand, mentions removing files that are already opened (aka POSIX semantics), and doesn't mentioned read-only files. os.Remove also supports that indirectly, as it uses Window's DeleteFileW, which internally use FILE_DISPOSITION_POSIX_SEMANTICS if the Windows version supports it. We can't unfortunately add support for POSIX semantics without Windows cooperation, and that feature is not available in "old" Windows versions.

[stanhu]

I updated the description to mention using FILE_DISPOSITION_POSIX_SEMANTICS.

As the comment in src/internal/syscall/windows/at_windows.go suggests, Windows 10, version 1607 (aka RS1) added support for FILE_DISPOSITION_POSIX_SEMANTICS, but Windows 2019 does not use this by default, as far as I can tell. At some point Microsoft enabled it by default; Windows 2022 appears to use FILE_DISPOSITION_POSIX_SEMANTICS by default.