Update after review

Src/IronPython/Modules/_io.cs

@@ -55,16 +55,13 @@ public static partial class PythonIOModule {
 
         private static int O_EXCL => RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? 0x400 : RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? 0x800 : 0x80;
 
-        [PythonHidden(PlatformsAttribute.PlatformFamily.Windows)]
         [SupportedOSPlatform("linux")]
         [SupportedOSPlatform("macos")]
         private static int O_CLOEXEC => RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? 0x1000000 : 0x80000;
 
-        [PythonHidden(PlatformsAttribute.PlatformFamily.Unix)]
         [SupportedOSPlatform("windows")]
         private static int O_BINARY => 0x8000;
 
-        [PythonHidden(PlatformsAttribute.PlatformFamily.Unix)]
         [SupportedOSPlatform("windows")]
         private static int O_NOINHERIT => 0x80;
 

Src/Scripts/generate_os_codes.py

@@ -199,7 +199,7 @@ def generate_O_flags(cw, flagvalues, access):
             if codes[darwin_idx] is None:
                 hidden_on += ["PlatformID.MacOSX"]
                 supported_on.discard(systems[darwin_idx])
-        if hidden_on:
+        if hidden_on and (access == 'public' or access == 'protected' or access == 'protected internal'):
             cw.write(f"[PythonHidden({', '.join(hidden_on)})]")
         if len(supported_on) != len(systems):
             for s in sorted(supported_on):

Tests/test_file.py

@@ -2,14 +2,15 @@
 # The .NET Foundation licenses this file to you under the Apache 2.0 License.
 # See the LICENSE file in the project root for more information.
 
+import errno
 import os
 import sys
 import unittest
 import _thread
 
 CP16623_LOCK = _thread.allocate_lock()
 
-from iptest import IronPythonTestCase, is_cli, is_cpython, is_netcoreapp, is_posix, is_linux, is_osx, is_windows, run_test, skipUnlessIronPython
+from iptest import IronPythonTestCase, is_cli, is_cpython, is_netcoreapp, is_posix, is_windows, run_test, skipUnlessIronPython
 
 class FileTest(IronPythonTestCase):
 
@@ -701,7 +702,7 @@ def test_errors(self):
 
         with self.assertRaises(OSError) as cm:
             open('path_too_long' * 100)
-        self.assertEqual(cm.exception.errno, (63 if is_osx else 36 if is_linux else 22) if is_netcoreapp and not is_posix or sys.version_info >= (3,6) else 2)
+        self.assertEqual(cm.exception.errno, (errno.ENAMETOOLONG if is_posix else errno.EINVAL) if is_netcoreapp and not is_posix or sys.version_info >= (3,6) else errno.ENOENT)
 
     def test_write_bytes(self):
         fname = self.temp_file