gh-127146: Update test skips for Emscripten 4.0.2 (#129474)

Updates test skips to reflect capabilities of Emscripten 4.0.2.

5 files changed, 61 insertions, 68 deletions

diff --git a/Lib/test/test_genericpath.py b/Lib/test/test_genericpath.py
index 391158b..6c3abe6 100644
--- a/Lib/test/test_genericpath.py
+++ b/Lib/test/test_genericpath.py
@@ -161,7 +161,6 @@ class GenericTest:
         self.assertIs(self.pathmodule.lexists(path=filename), True)
 
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
-    @unittest.skipIf(is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     def test_exists_fd(self):
         r, w = os.pipe()
         try:
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 455a87b..ac3b6d1 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -445,9 +445,6 @@ class IOTest(unittest.TestCase):
             self.assertRaises(exc, fp.seek, 1, self.SEEK_CUR)
             self.assertRaises(exc, fp.seek, -1, self.SEEK_END)
 
-    @unittest.skipIf(
-        support.is_emscripten, "fstat() of a pipe fd is not supported"
-    )
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
     def test_optional_abilities(self):
         # Test for OSError when optional APIs are not supported
@@ -501,57 +498,65 @@ class IOTest(unittest.TestCase):
             (text_reader, "r"), (text_writer, "w"),
             (self.BytesIO, "rws"), (self.StringIO, "rws"),
         )
-        for [test, abilities] in tests:
-            with self.subTest(test), test() as obj:
-                readable = "r" in abilities
-                self.assertEqual(obj.readable(), readable)
-                writable = "w" in abilities
-                self.assertEqual(obj.writable(), writable)
-
-                if isinstance(obj, self.TextIOBase):
-                    data = "3"
-                elif isinstance(obj, (self.BufferedIOBase, self.RawIOBase)):
-                    data = b"3"
-                else:
-                    self.fail("Unknown base class")
 
-                if "f" in abilities:
-                    obj.fileno()
-                else:
-                    self.assertRaises(OSError, obj.fileno)
+        def do_test(test, obj, abilities):
+            readable = "r" in abilities
+            self.assertEqual(obj.readable(), readable)
+            writable = "w" in abilities
+            self.assertEqual(obj.writable(), writable)
 
-                if readable:
-                    obj.read(1)
-                    obj.read()
-                else:
-                    self.assertRaises(OSError, obj.read, 1)
-                    self.assertRaises(OSError, obj.read)
+            if isinstance(obj, self.TextIOBase):
+                data = "3"
+            elif isinstance(obj, (self.BufferedIOBase, self.RawIOBase)):
+                data = b"3"
+            else:
+                self.fail("Unknown base class")
 
-                if writable:
-                    obj.write(data)
-                else:
-                    self.assertRaises(OSError, obj.write, data)
-
-                if sys.platform.startswith("win") and test in (
-                        pipe_reader, pipe_writer):
-                    # Pipes seem to appear as seekable on Windows
-                    continue
-                seekable = "s" in abilities
-                self.assertEqual(obj.seekable(), seekable)
-
-                if seekable:
-                    obj.tell()
-                    obj.seek(0)
-                else:
-                    self.assertRaises(OSError, obj.tell)
-                    self.assertRaises(OSError, obj.seek, 0)
+            if "f" in abilities:
+                obj.fileno()
+            else:
+                self.assertRaises(OSError, obj.fileno)
+
+            if readable:
+                obj.read(1)
+                obj.read()
+            else:
+                self.assertRaises(OSError, obj.read, 1)
+                self.assertRaises(OSError, obj.read)
+
+            if writable:
+                obj.write(data)
+            else:
+                self.assertRaises(OSError, obj.write, data)
+
+            if sys.platform.startswith("win") and test in (
+                    pipe_reader, pipe_writer):
+                # Pipes seem to appear as seekable on Windows
+                return
+            seekable = "s" in abilities
+            self.assertEqual(obj.seekable(), seekable)
+
+            if seekable:
+                obj.tell()
+                obj.seek(0)
+            else:
+                self.assertRaises(OSError, obj.tell)
+                self.assertRaises(OSError, obj.seek, 0)
+
+            if writable and seekable:
+                obj.truncate()
+                obj.truncate(0)
+            else:
+                self.assertRaises(OSError, obj.truncate)
+                self.assertRaises(OSError, obj.truncate, 0)
+
+        for [test, abilities] in tests:
+            with self.subTest(test):
+                if test == pipe_writer and not threading_helper.can_start_thread:
+                    skipTest()
+                with test() as obj:
+                    do_test(test, obj, abilities)
 
-                if writable and seekable:
-                    obj.truncate()
-                    obj.truncate(0)
-                else:
-                    self.assertRaises(OSError, obj.truncate)
-                    self.assertRaises(OSError, obj.truncate, 0)
 
     def test_open_handles_NUL_chars(self):
         fn_with_NUL = 'foo\0bar'
@@ -3927,7 +3932,6 @@ class TextIOWrapperTest(unittest.TestCase):
         self.assertEqual(res + f.readline(), 'foo\nbar\n')
 
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
-    @unittest.skipIf(support.is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     def test_read_non_blocking(self):
         import os
         r, w = os.pipe()
@@ -4242,9 +4246,6 @@ class MiscIOTest(unittest.TestCase):
                 self.open(os_helper.TESTFN, mode)
             self.assertIn('invalid mode', str(cm.exception))
 
-    @unittest.skipIf(
-        support.is_emscripten, "fstat() of a pipe fd is not supported"
-    )
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
     def test_open_pipe_with_append(self):
         # bpo-27805: Ignore ESPIPE from lseek() in open().
@@ -4413,15 +4414,11 @@ class MiscIOTest(unittest.TestCase):
                         with self.assertRaisesRegex(TypeError, msg):
                             pickle.dumps(f, protocol)
 
-    @unittest.skipIf(
-        support.is_emscripten, "fstat() of a pipe fd is not supported"
-    )
+    @unittest.skipIf(support.is_emscripten, "Emscripten corrupts memory when writing to nonblocking fd")
     def test_nonblock_pipe_write_bigbuf(self):
         self._test_nonblock_pipe_write(16*1024)
 
-    @unittest.skipIf(
-        support.is_emscripten, "fstat() of a pipe fd is not supported"
-    )
+    @unittest.skipIf(support.is_emscripten, "Emscripten corrupts memory when writing to nonblocking fd")
     def test_nonblock_pipe_write_smallbuf(self):
         self._test_nonblock_pipe_write(1024)
 
diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
index da01c65..c10387b 100644
--- a/Lib/test/test_ntpath.py
+++ b/Lib/test/test_ntpath.py
@@ -940,7 +940,6 @@ class TestNtpath(NtpathTestCase):
         self.assertRaises(TypeError, ntpath.commonpath, ['C:\\Foo', b'Foo\\Baz'])
         self.assertRaises(TypeError, ntpath.commonpath, ['Foo', b'C:\\Foo\\Baz'])
 
-    @unittest.skipIf(is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     def test_sameopenfile(self):
         with TemporaryFile() as tf1, TemporaryFile() as tf2:
             # Make sure the same file is really the same
diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index 1497a98..6d62d61 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -253,7 +253,6 @@ class WakeupFDTests(unittest.TestCase):
         self.assertRaises((ValueError, OSError),
                           signal.set_wakeup_fd, fd)
 
-    @unittest.skipIf(support.is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
     def test_set_wakeup_fd_result(self):
         r1, w1 = os.pipe()
@@ -272,7 +271,6 @@ class WakeupFDTests(unittest.TestCase):
         self.assertEqual(signal.set_wakeup_fd(-1), w2)
         self.assertEqual(signal.set_wakeup_fd(-1), -1)
 
-    @unittest.skipIf(support.is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     @unittest.skipUnless(support.has_socket_support, "needs working sockets.")
     def test_set_wakeup_fd_socket_result(self):
         sock1 = socket.socket()
@@ -293,7 +291,6 @@ class WakeupFDTests(unittest.TestCase):
     # On Windows, files are always blocking and Windows does not provide a
     # function to test if a socket is in non-blocking mode.
     @unittest.skipIf(sys.platform == "win32", "tests specific to POSIX")
-    @unittest.skipIf(support.is_emscripten, "Fixed in next Emscripten release after 4.0.1")
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
     def test_set_wakeup_fd_blocking(self):
         rfd, wfd = os.pipe()
diff --git a/Tools/wasm/README.md b/Tools/wasm/README.md
index 2e0fa2f..62aa87a 100644
--- a/Tools/wasm/README.md
+++ b/Tools/wasm/README.md
@@ -24,8 +24,9 @@ https://github.com/psf/webassembly for more information.
 To cross compile to the ``wasm32-emscripten`` platform you need
 [the Emscripten compiler toolchain](https://emscripten.org/), 
 a Python interpreter, and an installation of Node version 18 or newer.
-Emscripten version 3.1.73 or newer is recommended. All commands below are
-relative to a checkout of the Python repository.
+Emscripten version 4.0.2 is recommended; newer versions may also work, but all
+official testing is performed with that version. All commands below are relative
+to a checkout of the Python repository.
 
 #### Install [the Emscripten compiler toolchain](https://emscripten.org/docs/getting_started/downloads.html)
 
@@ -266,7 +267,7 @@ if os.name == "posix":
 posix.uname_result(
     sysname='Emscripten',
     nodename='emscripten',
-    release='3.1.19',
+    release='4.0.2',
     version='#1',
     machine='wasm32'
 )