pythongh-109425: regrtest decodes worker stdout with backslashreplace

libregrtest now decodes stdout of test worker processes with the
"backslashreplace" error handler to log corrupted stdout, instead of
failing with an error and not logging the stdout.

Lib/test/libregrtest/run_workers.py

@@ -218,7 +218,9 @@ def create_stdout(self, stack: contextlib.ExitStack) -> TextIO:
 
         # gh-94026: Write stdout+stderr to a tempfile as workaround for
         # non-blocking pipes on Emscripten with NodeJS.
-        stdout_file = tempfile.TemporaryFile('w+', encoding=encoding)
+        stdout_file = tempfile.TemporaryFile('w+',
+                                             encoding=encoding,
+                                             errors='backslashreplace')
         stack.enter_context(stdout_file)
         return stdout_file
 

Lib/test/test_regrtest.py

@@ -421,10 +421,12 @@ def regex_search(self, regex, output):
             self.fail("%r not found in %r" % (regex, output))
         return match
 
-    def check_line(self, output, regex, full=False):
+    def check_line(self, output, pattern, full=False, regex=True):
+        if not regex:
+            pattern = re.escape(pattern)
         if full:
-            regex += '\n'
-        regex = re.compile(r'^' + regex, re.MULTILINE)
+            pattern += '\n'
+        regex = re.compile(r'^' + pattern, re.MULTILINE)
         self.assertRegex(output, regex)
 
     def parse_executed_tests(self, output):
@@ -1755,7 +1757,7 @@ def test_leak_tmp_file(self):
                           f"files (1): mytmpfile",
                           output)
 
-    def test_mp_decode_error(self):
+    def test_worker_decode_error(self):
         # gh-101634: If a worker stdout cannot be decoded, report a failed test
         # and a non-zero exit code.
         if sys.platform == 'win32':
@@ -1767,29 +1769,40 @@ def test_mp_decode_error(self):
                 if encoding is None:
                     self.skipTest("cannot get regrtest worker encoding")
 
-        nonascii = b"byte:\xa0\xa9\xff\n"
+        nonascii = bytes(ch for ch in range(128, 256))
+        corrupted_output = b"nonascii:%s\n" % (nonascii,)
+        # gh-108989: On Windows, assertion errors are written in UTF-16
+        assertion_failed = 'Assertion failed: tstate_is_alive(tstate)\n'
+        corrupted_output += assertion_failed.encode('utf-16-le')
         try:
-            nonascii.decode(encoding)
+            corrupted_output.decode(encoding)
         except UnicodeDecodeError:
             pass
         else:
-            self.skipTest(f"{encoding} can decode non-ASCII bytes {nonascii!a}")
+            self.skipTest(f"{encoding} can decode non-ASCII bytes")
+
+        expected_line = corrupted_output.decode(encoding, 'backslashreplace')
 
         code = textwrap.dedent(fr"""
             import sys
+            import unittest
+
+            class Tests(unittest.TestCase):
+                def test_pass(self):
+                    pass
+
             # bytes which cannot be decoded from UTF-8
-            nonascii = {nonascii!a}
-            sys.stdout.buffer.write(nonascii)
+            corrupted_output = {corrupted_output!a}
+            sys.stdout.buffer.write(corrupted_output)
             sys.stdout.buffer.flush()
         """)
         testname = self.create_test(code=code)
 
-        output = self.run_tests("--fail-env-changed", "-v", "-j1", testname,
-                                exitcode=EXITCODE_BAD_TEST)
+        output = self.run_tests("--fail-env-changed", "-v", "-j1", testname)
         self.check_executed_tests(output, [testname],
-                                  failed=[testname],
                                   parallel=True,
-                                  stats=0)
+                                  stats=1)
+        self.check_line(output, expected_line, regex=False)
 
     def test_doctest(self):
         code = textwrap.dedent(r'''

Misc/NEWS.d/next/Tests/2023-09-14-23-27-40.gh-issue-109425.j-uFep.rst

@@ -0,0 +1,3 @@
+libregrtest now decodes stdout of test worker processes with the
+"backslashreplace" error handler to log corrupted stdout, instead of failing
+with an error and not logging the stdout. Patch by Victor Stinner.