procutil: make stream detection in make_line_buffered more correct and strict
In make_line_buffered(), we don’t want to wrap the stream if we know that lines
get flushed to the underlying raw stream already.
Previously, the heuristic was too optimistic. It assumed that any stream which
is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there
are buffered streams that aren’t instances of io.BufferedIOBase, like
Mercurial’s own winstdout.
The new logic is different in two ways:
First, only for the check, if unwraps any combination of WriteAllWrapper and
winstdout.
Second, it skips wrapping the stream only if it is an instance of io.RawIOBase
(or already wrapped). If it is an instance of io.BufferedIOBase, it gets
wrapped. In any other case, the function raises an exception. This ensures
that, if an unknown stream is passed or we add another wrapper in the future,
we don’t wrap the stream if it’s already line buffered or not wrap the stream
if it’s not line buffered. In fact, this was already helpful during development
of this change. Without it, I possibly would have forgot that WriteAllWrapper
needs to be ignored for the check, leading to unnecessary wrapping if stdout is
unbuffered.
The alternative would have been to always wrap unknown streams. However, I
don’t think that anyone would benefit from being less strict. We can expect
streams from the standard library to be subclassing either io.RawIOBase or
io.BufferedIOBase, so running Mercurial in the standard way should not regress
by this change. Py2exe might replace sys.stdout and sys.stderr, but that
currently breaks Mercurial anyway and also these streams don’t claim to be
interactive, so this function is not called for them.
# hgdemandimport - global demand-loading of modules for Mercurial
#
# Copyright 2017 Facebook Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''demandimport - automatic demand-loading of modules'''
# This is in a separate package from mercurial because in Python 3,
# demand loading is per-package. Keeping demandimport in the mercurial package
# would disable demand loading for any modules in mercurial.
import os
import sys
from . import demandimportpy3 as demandimport
# Full module names which can't be lazy imported.
# Extensions can add to this set.
IGNORES = {
'__future__',
'_hashlib',
# ImportError during pkg_resources/__init__.py:fixup_namespace_package
'_imp',
'_xmlplus',
'fcntl',
'nt', # pathlib2 tests the existence of built-in 'nt' module
'win32com.gen_py',
'win32com.shell', # 'appdirs' tries to import win32com.shell
'_winreg', # 2.7 mimetypes needs immediate ImportError
'pythoncom',
# imported by tarfile, not available under Windows
'pwd',
'grp',
# imported by profile, itself imported by hotshot.stats,
# not available under Windows
'resource',
# this trips up many extension authors
'gtk',
# setuptools' pkg_resources.py expects "from __main__ import x" to
# raise ImportError if x not defined
'__main__',
'_ast', # https://bugs.python.org/issue41631
'_ssl', # conditional imports in the stdlib, issue1964
'_sre', # issue4920
'rfc822',
'mimetools',
'sqlalchemy.events', # has import-time side effects (issue5085)
'sqlalchemy.dialects', # similar problems as above
# setuptools 8 expects this module to explode early when not on windows
'distutils.msvc9compiler',
'__builtin__',
'builtins',
'urwid.command_map', # for pudb
'lzma',
}
_pypy = '__pypy__' in sys.builtin_module_names
if _pypy:
# _ctypes.pointer is shadowed by "from ... import pointer" (PyPy 5)
IGNORES.add('_ctypes.pointer')
# pure Python module on PyPy, must be loaded to raise ModuleNotFoundError
# on non-Windows platforms
IGNORES.add('msvcrt')
demandimport.init(IGNORES)
# Re-export.
isenabled = demandimport.isenabled
disable = demandimport.disable
deactivated = demandimport.deactivated
def enable():
# chg pre-imports modules so do not enable demandimport for it
if (
'CHGINTERNALMARK' not in os.environ
and os.environ.get('HGDEMANDIMPORT') != 'disable'
):
demandimport.enable()