pythongh-84461: Fix Emscripten umask and permission issues (pythonGH-94002)

- Emscripten's default umask is too strict, see
  emscripten-core/emscripten#17269
- getuid/getgid and geteuid/getegid are stubs that always return 0
  (root). Disable effective uid/gid syscalls and fix tests that use
  chmod() current user.
- Cannot drop X bit from directory.

(cherry picked from commit 2702e40)

Author: tiran

Lib/test/libregrtest/main.py

@@ -600,6 +600,16 @@ def save_xml_result(self):
             for s in ET.tostringlist(root):
                 f.write(s)
 
+    def fix_umask(self):
+        if support.is_emscripten:
+            # Emscripten has default umask 0o777, which breaks some tests.
+            # see https://github.com/emscripten-core/emscripten/issues/17269
+            old_mask = os.umask(0)
+            if old_mask == 0o777:
+                os.umask(0o027)
+            else:
+                os.umask(old_mask)
+
     def set_temp_dir(self):
         if self.ns.tempdir:
             self.tmp_dir = self.ns.tempdir
@@ -660,6 +670,8 @@ def main(self, tests=None, **kwargs):
 
         self.set_temp_dir()
 
+        self.fix_umask()
+
         if self.ns.cleanup:
             self.cleanup()
             sys.exit(0)

Lib/test/test_posix.py

@@ -787,6 +787,7 @@ def check_stat(uid, gid):
             check_stat(uid, gid)
 
     @os_helper.skip_unless_working_chmod
+    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
     def test_chown(self):
         # raise an OSError if the file does not exist
         os.unlink(os_helper.TESTFN)
@@ -798,6 +799,7 @@ def test_chown(self):
 
     @os_helper.skip_unless_working_chmod
     @unittest.skipUnless(hasattr(posix, 'fchown'), "test needs os.fchown()")
+    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
     def test_fchown(self):
         os.unlink(os_helper.TESTFN)
 
@@ -1356,6 +1358,7 @@ def test_chmod_dir_fd(self):
 
     @unittest.skipUnless(hasattr(os, 'chown') and (os.chown in os.supports_dir_fd),
                          "test needs dir_fd support in os.chown()")
+    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
     def test_chown_dir_fd(self):
         with self.prepare_file() as (dir_fd, name, fullname):
             posix.chown(name, os.getuid(), os.getgid(), dir_fd=dir_fd)

Lib/test/test_pydoc.py

@@ -950,6 +950,7 @@ def test_apropos_with_unreadable_dir(self):
         self.assertEqual(err.getvalue(), '')
 
     @os_helper.skip_unless_working_chmod
+    @unittest.skipIf(is_emscripten, "cannot remove x bit")
     def test_apropos_empty_doc(self):
         pkgdir = os.path.join(TESTFN, 'walkpkg')
         os.mkdir(pkgdir)