ValueError: illegal newline value on 0x85 (NEL)

In attempting to harmonize the path pie implementation with more modern constructs, I'm seeking also to utilize the newline argument to open instead of explicitly substituting characters.

When I do, however, I find that some tests start to fail when NEL is passed as a newline character:

$ py -c "open('foo', 'w', newline='\x85')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: illegal newline value: …

At least in some contexts, Python recognizes NEL as a line separator:

>>> 'a\x85b\x1ec'.splitlines()
['a', 'b', 'c']

See also #66428 for some background.

According to the wikipedia article, a conforming application should honor a number of characters as newlines:

>>> newlines = '\x0a', '\x0b', '\x0c', '\x0d', '\x0d\x0a', '\u0085', '\u2028', '\u2029'
>>> for candidate in newlines:
...   try: x=open('foo', 'w', newline=candidate)
...   except ValueError: print('failed on', repr(candidate))
... 
failed on '\x0b'
failed on '\x0c'
failed on '\x85'
failed on '\u2028'
failed on '\u2029'

Comece com o reproducer relatado de open(..., newline=...) e compare-o com str.splitlines() para os caracteres de nova linha listados. Rastreie o tratamento de I/O de texto do CPython para a validação de newline e, em seguida, identifique ou adicione os testes relevantes. A tarefa estará concluída quando os valores de newline pretendidos tiverem um comportamento definido e testado, sem regredir a tradução existente de newline.