bpo-40280: Block more non-working syscalls in Emscripten (GH-31757)

- getgroups always fails.
- geteuid and getegid always return 0 (root), which confuse tarfile and
  tests.
- hardlinks (link, linkat) always fails.
- non-encodable file names are not supported by NODERAWFS layer.
- mark more tests with dependency on subprocess and multiprocessing.
  Mocking does not work if the module fails to import.

Lib/distutils/tests/test_file_util.py

@@ -79,6 +79,7 @@ class FileUtilTestCase(support.TempdirManager, unittest.TestCase):
                 fobj.write('spam eggs')
             move_file(self.source, self.target, verbose=0)
 
+    @unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
     def test_copy_file_hard_link(self):
         with open(self.source, 'w') as f:
             f.write('some content')
@@ -99,6 +100,7 @@ class FileUtilTestCase(support.TempdirManager, unittest.TestCase):
         with open(self.source, 'r') as f:
             self.assertEqual(f.read(), 'some content')
 
+    @unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
     def test_copy_file_hard_link_failure(self):
         # If hard linking fails, copy_file() falls back on copying file
         # (some special filesystems don't support hard linking even under

Lib/test/support/os_helper.py

@@ -49,8 +49,8 @@ if os.name == 'nt':
                   'encoding (%s). Unicode filename tests may not be effective'
                   % (TESTFN_UNENCODABLE, sys.getfilesystemencoding()))
             TESTFN_UNENCODABLE = None
-# Mac OS X denies unencodable filenames (invalid utf-8)
-elif sys.platform != 'darwin':
+# macOS and Emscripten deny unencodable filenames (invalid utf-8)
+elif sys.platform not in {'darwin', 'emscripten'}:
     try:
         # ascii and utf-8 cannot encode the byte 0xff
         b'\xff'.decode(sys.getfilesystemencoding())

Lib/test/test_compileall.py

@@ -244,6 +244,7 @@ class CompileallTestsBase:
         self.assertFalse(pool_mock.called)
         self.assertTrue(compile_file_mock.called)
 
+    @skipUnless(_have_multiprocessing, "requires multiprocessing")
     @mock.patch('concurrent.futures.ProcessPoolExecutor', new=None)
     @mock.patch('compileall.compile_file')
     def test_compile_missing_multiprocessing(self, compile_file_mock):
@@ -296,6 +297,7 @@ class CompileallTestsBase:
         """Recursive compile_dir ddir= contains package paths; bpo39769."""
         return self._test_ddir_only(ddir="<a prefix>", parallel=False)
 
+    @skipUnless(_have_multiprocessing, "requires multiprocessing")
     def test_ddir_multiple_workers(self):
         """Recursive compile_dir ddir= contains package paths; bpo39769."""
         return self._test_ddir_only(ddir="<a prefix>", parallel=True)
@@ -304,6 +306,7 @@ class CompileallTestsBase:
         """Recursive compile_dir ddir='' contains package paths; bpo39769."""
         return self._test_ddir_only(ddir="", parallel=False)
 
+    @skipUnless(_have_multiprocessing, "requires multiprocessing")
     def test_ddir_empty_multiple_workers(self):
         """Recursive compile_dir ddir='' contains package paths; bpo39769."""
         return self._test_ddir_only(ddir="", parallel=True)
@@ -924,6 +927,7 @@ class CommandLineTestsNoSourceEpoch(CommandLineTestsBase,
 
 
 
+@unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
 class HardlinkDedupTestsBase:
     # Test hardlink_dupes parameter of compileall.compile_dir()
 

Lib/test/test_genericpath.py

@@ -7,6 +7,7 @@ import os
 import sys
 import unittest
 import warnings
+from test.support import is_emscripten
 from test.support import os_helper
 from test.support import warnings_helper
 from test.support.script_helper import assert_python_ok
@@ -154,6 +155,7 @@ class GenericTest:
             self.assertIs(self.pathmodule.lexists(bfilename + b'\x00'), False)
 
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
+    @unittest.skipIf(is_emscripten, "Emscripten pipe fds have no stat")
     def test_exists_fd(self):
         r, w = os.pipe()
         try:
@@ -246,6 +248,7 @@ class GenericTest:
     def test_samefile_on_symlink(self):
         self._test_samefile_on_link_func(os.symlink)
 
+    @unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
     def test_samefile_on_link(self):
         try:
             self._test_samefile_on_link_func(os.link)
@@ -288,6 +291,7 @@ class GenericTest:
     def test_samestat_on_symlink(self):
         self._test_samestat_on_link_func(os.symlink)
 
+    @unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
     def test_samestat_on_link(self):
         try:
             self._test_samestat_on_link_func(os.link)
@@ -476,11 +480,11 @@ class CommonTest(GenericTest):
 
     def test_nonascii_abspath(self):
         if (os_helper.TESTFN_UNDECODABLE
-        # Mac OS X denies the creation of a directory with an invalid
-        # UTF-8 name. Windows allows creating a directory with an
+        # macOS and Emscripten deny the creation of a directory with an
+        # invalid UTF-8 name. Windows allows creating a directory with an
         # arbitrary bytes name, but fails to enter this directory
         # (when the bytes name is used).
-        and sys.platform not in ('win32', 'darwin')):
+        and sys.platform not in ('win32', 'darwin', 'emscripten')):
             name = os_helper.TESTFN_UNDECODABLE
         elif os_helper.TESTFN_NONASCII:
             name = os_helper.TESTFN_NONASCII

Lib/test/test_os.py

@@ -2203,6 +2203,7 @@ class TestInvalidFD(unittest.TestCase):
         self.check(os.set_blocking, True)
 
 
+@unittest.skipUnless(hasattr(os, 'link'), 'requires os.link')
 class LinkTests(unittest.TestCase):
     def setUp(self):
         self.file1 = os_helper.TESTFN

Lib/test/test_posix.py

@@ -75,8 +75,9 @@ class PosixTester(unittest.TestCase):
         for name in NO_ARG_FUNCTIONS:
             posix_func = getattr(posix, name, None)
             if posix_func is not None:
-                posix_func()
-                self.assertRaises(TypeError, posix_func, 1)
+                with self.subTest(name):
+                    posix_func()
+                    self.assertRaises(TypeError, posix_func, 1)
 
     @unittest.skipUnless(hasattr(posix, 'getresuid'),
                          'test needs posix.getresuid()')
@@ -1399,7 +1400,10 @@ class TestPosixDirFd(unittest.TestCase):
                     # whoops!  using both together not supported on this platform.
                     pass
 
-    @unittest.skipUnless(os.link in os.supports_dir_fd, "test needs dir_fd support in os.link()")
+    @unittest.skipUnless(
+        hasattr(os, "link") and os.link in os.supports_dir_fd,
+        "test needs dir_fd support in os.link()"
+    )
     def test_link_dir_fd(self):
         with self.prepare_file() as (dir_fd, name, fullname), \
              self.prepare() as (dir_fd2, linkname, fulllinkname):

Lib/test/test_script_helper.py

@@ -3,7 +3,7 @@
 import subprocess
 import sys
 import os
-from test.support import script_helper
+from test.support import script_helper, requires_subprocess
 import unittest
 from unittest import mock
 
@@ -69,6 +69,7 @@ class TestScriptHelper(unittest.TestCase):
             self.assertNotIn('-E', popen_command)
 
 
+@requires_subprocess()
 class TestScriptHelperEnvironment(unittest.TestCase):
     """Code coverage for interpreter_requires_environment()."""
 

Tools/wasm/config.site-wasm32-emscripten

@@ -86,11 +86,22 @@ ac_cv_func_mkfifoat=no
 ac_cv_func_mknod=no
 ac_cv_func_mknodat=no
 
-# always fails with permission error
+# always fails with permission or not implemented error
+ac_cv_func_getgroups=no
 ac_cv_func_setgroups=no
 ac_cv_func_setresuid=no
 ac_cv_func_setresgid=no
 
+# Emscripten geteuid() / getegid() always return 0 (root), which breaks
+# assumption in tarfile module and some tests.
+ac_cv_func_getegid=no
+ac_cv_func_geteuid=no
+
+# Emscripten does not support hard links, always fails with errno 34
+# "Too many links". See emscripten_syscall_stubs.c
+ac_cv_func_link=no
+ac_cv_func_linkat=no
+
 # alarm signal is not delivered, may need a callback into the event loop?
 ac_cv_func_alarm=no