[issue27938] PyUnicode_AsEncodedString, PyUnicode_Decode: add fast-path for "us-ascii" encoding

[Martin Panter]

Martin Panter added the comment:

It seems this change is the cause of the Free BSD buildbot failures. From memory, both failing cases involve sending or receiving non-ASCII bytes in child Python processes.

http://buildbot.python.org/all/builders/AMD64%20FreeBSD%20CURRENT%20Non-Debug%203.x/builds/110/steps/test/logs/stdio

======================================================================
FAIL: test_non_ascii (test.test_cmd_line_script.CmdLineTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-current.nondebug/build/Lib/test/test_cmd_line_script.py", line 517, in test_non_ascii
    rc, stdout, stderr = assert_python_ok(script_name)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-current.nondebug/build/Lib/test/support/script_helper.py", line 139, in assert_python_ok
    return _assert_python(True, *args, **env_vars)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-current.nondebug/build/Lib/test/support/script_helper.py", line 125, in _assert_python
    err))
AssertionError: Process return code is 1
command line: ['/usr/home/buildbot/python/3.x.koobs-freebsd-current.nondebug/build/python', '-X', 'faulthandler', '-I', './@test_60885_tmp\udce7w\udcf0.py']

stdout:
---

---

stderr:
---
UnicodeEncodeError: 'ascii' codec can't encode character '\xe7' in position 17: ordinal not in range(128)
---

======================================================================
FAIL: test_nonascii (test.test_readline.TestReadline)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-current.nondebug/build/Lib/test/test_readline.py", line 203, in test_nonascii
    self.assertIn(b"text 't\\xeb'\r\n", output)
AssertionError: b"text 't\\xeb'\r\n" not found in bytearray(b"^A^B^B^B^B^B^B^B\t\tx\t\r\n[\x07\r\x07\x07\x07\x07\x07\x07\x07\x07x[\x08\x07\r\nresult \'x[\'\r\nhistory \'x[\'\r\n")

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nosy: +martin.panter

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<http://bugs.python.org/issue27938>
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