Test test_embed fails on Windows 11, Python 3.13.0a0

[bityob]

Bug report

The test test_embed fails on my Windows machine, using master branch (commit d0972c7).

python.bat -m test test_embed

Full output -

C:\Code\cpython>python.bat -m test test_embed
Running Debug|x64 interpreter...
0:00:00 Run tests sequentially
0:00:00 [1/1] test_embed
test test_embed failed -- Traceback (most recent call last):
  File "C:\Code\cpython\Lib\test\test_embed.py", line 259, in test_forced_io_encoding
    self.assertEqual(out.strip(), expected_output)
AssertionError: '--- [403 chars]din: utf-8:surrogateescape\nstdout: iso8859-1:[221 chars]lace' != '--- [403 chars]din: iso8859-1:surrogateescape\nstdout: iso885[229 chars]lace'
  --- Use defaults ---
  Expected encoding: default
  Expected errors: default
  stdin: utf-8:surrogateescape
  stdout: utf-8:surrogateescape
  stderr: utf-8:backslashreplace
  --- Set errors only ---
  Expected encoding: default
  Expected errors: ignore
  stdin: utf-8:ignore
  stdout: utf-8:ignore
  stderr: utf-8:backslashreplace
  --- Set encoding only ---
  Expected encoding: iso8859-1
  Expected errors: default
- stdin: utf-8:surrogateescape
?        ^^^ ^
+ stdin: iso8859-1:surrogateescape
?        ^^^^^^^ ^
  stdout: iso8859-1:surrogateescape
  stderr: iso8859-1:backslashreplace
  --- Set encoding and errors ---
  Expected encoding: iso8859-1
  Expected errors: replace
- stdin: utf-8:replace
+ stdin: iso8859-1:replace
  stdout: iso8859-1:replace
  stderr: iso8859-1:backslashreplace


test_embed failed (1 failure) in 30.7 sec

== Tests result: FAILURE ==

1 test failed:
    test_embed

Total duration: 30.7 sec
Tests result: FAILURE

Your environment

• CPython versions tested on:

Running Debug|x64 interpreter...
Python 3.13.0a0

• Commit: d0972c7
• Operating system and architecture:

OS Name:                   Microsoft Windows 11 Pro
OS Version:                10.0.22621 N/A Build 22621

Linked PRs

• gh-106659: Fix test_embed.test_forced_io_encoding() on Windows #108010

[eryksun]

The test doesn't override sys.stdin in the child process. Thus when it's run normally, stdin is a console file. By default, the raw type of a console file is io._WindowsConsoleIO, which always uses UTF-8. The test expects to be able to override this, but being able to do this will either require forcing stdin to be a pipe or nul or it will require defining the environment variable PYTHONLEGACYWINDOWSSTDIO. The latter forces the use of io.FileIO for console files, instead of io._WindowsConsoleIO.

[Eclips4]

Bisected to #105154
cc @vstinner

[vstinner]

Bisected to #105154 cc @vstinner

Oh thanks for the bisect! I wrote PR #108010 to fix the regression. I'm able to reproduce the test failure on Windows when I run the test manually in a terminal.

[vstinner]

The test expects to be able to override this, but being able to do this will either require forcing stdin to be a pipe or nul or it will require defining the environment variable PYTHONLEGACYWINDOWSSTDIO.

The removed Py_SetStandardStreamEncoding() function did set Py_LegacyWindowsStdioFlag:

        /* Overriding the stream encoding implies legacy streams */
        Py_LegacyWindowsStdioFlag = 1;

I missed that in my change. My PR fix it.

[vstinner]

It should now be fixed. Thanks for your bug report! Thanks @Eclips4 for your review on my PR.