syscall: let ENOSYS, ENOTSUP and EOPNOTSUPP implement errors.ErrUnsup…

…ported

As suggested by Bryan, also update (Errno).Is on windows to include the
missing oserror cases that are covered on other platforms.

Quoting Bryan:
> Windows syscalls don't actually return those errors, but the dummy Errno
> constants defined on Windows should still have the same meaning as on
> Unix.

Updates #41198

Change-Id: I15441abde4a7ebaa3c6518262c052530cd2add4b
Reviewed-on: https://go-review.googlesource.com/c/go/+/476875
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

src/internal/testenv/testenv_unix.go

@@ -24,11 +24,6 @@ func syscallIsNotSupported(err error) bool {
 	var errno syscall.Errno
 	if errors.As(err, &errno) {
 		switch errno {
-		case syscall.ENOSYS, syscall.ENOTSUP:
-			// Explicitly not supported.
-			// TODO(#41198): remove these cases when errors.Is reports that they are
-			// equivalent to ErrUnsupported.
-			return true
 		case syscall.EPERM, syscall.EROFS:
 			// User lacks permission: either the call requires root permission and the
 			// user is not root, or the call is denied by a container security policy.

src/syscall/syscall_js.go

@@ -7,6 +7,7 @@
 package syscall
 
 import (
+	errorspkg "errors"
 	"internal/itoa"
 	"internal/oserror"
 	"sync"
@@ -47,8 +48,8 @@ const PathMax = 256
 //		err = errno
 //	}
 //
-// Errno values can be tested against error values from the os package
-// using errors.Is. For example:
+// Errno values can be tested against error values using errors.Is.
+// For example:
 //
 //	_, _, err := syscall.Syscall(...)
 //	if errors.Is(err, fs.ErrNotExist) ...
@@ -72,6 +73,8 @@ func (e Errno) Is(target error) bool {
 		return e == EEXIST || e == ENOTEMPTY
 	case oserror.ErrNotExist:
 		return e == ENOENT
+	case errorspkg.ErrUnsupported:
+		return e == ENOSYS || e == ENOTSUP || e == EOPNOTSUPP
 	}
 	return false
 }

src/syscall/syscall_plan9.go

@@ -23,8 +23,8 @@ const bitSize16 = 2
 
 // ErrorString implements Error's String method by returning itself.
 //
-// ErrorString values can be tested against error values from the os package
-// using errors.Is. For example:
+// ErrorString values can be tested against error values using errors.Is.
+// For example:
 //
 //	_, _, err := syscall.Syscall(...)
 //	if errors.Is(err, fs.ErrNotExist) ...

src/syscall/syscall_unix.go

@@ -7,6 +7,7 @@
 package syscall
 
 import (
+	errorspkg "errors"
 	"internal/bytealg"
 	"internal/itoa"
 	"internal/oserror"
@@ -97,8 +98,8 @@ func (m *mmapper) Munmap(data []byte) (err error) {
 //		err = errno
 //	}
 //
-// Errno values can be tested against error values from the os package
-// using errors.Is. For example:
+// Errno values can be tested against error values using errors.Is.
+// For example:
 //
 //	_, _, err := syscall.Syscall(...)
 //	if errors.Is(err, fs.ErrNotExist) ...
@@ -122,6 +123,8 @@ func (e Errno) Is(target error) bool {
 		return e == EEXIST || e == ENOTEMPTY
 	case oserror.ErrNotExist:
 		return e == ENOENT
+	case errorspkg.ErrUnsupported:
+		return e == ENOSYS || e == ENOTSUP || e == EOPNOTSUPP
 	}
 	return false
 }

src/syscall/syscall_windows.go

@@ -103,8 +103,8 @@ func UTF16PtrFromString(s string) (*uint16, error) {
 
 // Errno is the Windows error number.
 //
-// Errno values can be tested against error values from the os package
-// using errors.Is. For example:
+// Errno values can be tested against error values using errors.Is.
+// For example:
 //
 //	_, _, err := syscall.Syscall(...)
 //	if errors.Is(err, fs.ErrNotExist) ...
@@ -147,17 +147,25 @@ const _ERROR_BAD_NETPATH = Errno(53)
 func (e Errno) Is(target error) bool {
 	switch target {
 	case oserror.ErrPermission:
-		return e == ERROR_ACCESS_DENIED
+		return e == ERROR_ACCESS_DENIED ||
+			e == EACCES ||
+			e == EPERM
 	case oserror.ErrExist:
 		return e == ERROR_ALREADY_EXISTS ||
 			e == ERROR_DIR_NOT_EMPTY ||
-			e == ERROR_FILE_EXISTS
+			e == ERROR_FILE_EXISTS ||
+			e == EEXIST ||
+			e == ENOTEMPTY
 	case oserror.ErrNotExist:
 		return e == ERROR_FILE_NOT_FOUND ||
 			e == _ERROR_BAD_NETPATH ||
-			e == ERROR_PATH_NOT_FOUND
+			e == ERROR_PATH_NOT_FOUND ||
+			e == ENOENT
 	case errorspkg.ErrUnsupported:
-		return e == EWINDOWS
+		return e == ENOSYS ||
+			e == ENOTSUP ||
+			e == EOPNOTSUPP ||
+			e == EWINDOWS
 	}
 	return false
 }