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.
# policy.py - module policy logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
import os
import sys
from .pycompat import getattr
# Rules for how modules can be loaded. Values are:
#
# c - require C extensions
# rust+c - require Rust and C extensions
# rust+c-allow - allow Rust and C extensions with fallback to pure Python
# for each
# allow - allow pure Python implementation when C loading fails
# cffi - required cffi versions (implemented within pure module)
# cffi-allow - allow pure Python implementation if cffi version is missing
# py - only load pure Python modules
#
# By default, fall back to the pure modules so the in-place build can
# run without recompiling the C extensions. This will be overridden by
# __modulepolicy__ generated by setup.py.
policy = b'allow'
_packageprefs = {
# policy: (versioned package, pure package)
b'c': ('cext', None),
b'allow': ('cext', 'pure'),
b'cffi': ('cffi', None),
b'cffi-allow': ('cffi', 'pure'),
b'py': (None, 'pure'),
# For now, rust policies impact importrust only
b'rust+c': ('cext', None),
b'rust+c-allow': ('cext', 'pure'),
}
try:
from . import __modulepolicy__
policy = __modulepolicy__.modulepolicy
except ImportError:
pass
# PyPy doesn't load C extensions.
#
# The canonical way to do this is to test platform.python_implementation().
# But we don't import platform and don't bloat for it here.
if '__pypy__' in sys.builtin_module_names:
policy = b'cffi'
# Environment variable can always force settings.
if 'HGMODULEPOLICY' in os.environ:
policy = os.environ['HGMODULEPOLICY'].encode('utf-8')
def _importfrom(pkgname, modname):
# from .<pkgname> import <modname> (where . is looked through this module)
fakelocals = {}
pkg = __import__(pkgname, globals(), fakelocals, [modname], level=1)
try:
fakelocals[modname] = mod = getattr(pkg, modname)
except AttributeError:
raise ImportError('cannot import name %s' % modname)
# force import; fakelocals[modname] may be replaced with the real module
getattr(mod, '__doc__', None)
return fakelocals[modname]
# keep in sync with "version" in C modules
_cextversions = {
('cext', 'base85'): 1,
('cext', 'bdiff'): 3,
('cext', 'mpatch'): 1,
('cext', 'osutil'): 4,
('cext', 'parsers'): 20,
}
# map import request to other package or module
_modredirects = {
('cext', 'charencode'): ('cext', 'parsers'),
('cffi', 'base85'): ('pure', 'base85'),
('cffi', 'charencode'): ('pure', 'charencode'),
('cffi', 'parsers'): ('pure', 'parsers'),
}
def _checkmod(pkgname, modname, mod):
expected = _cextversions.get((pkgname, modname))
actual = getattr(mod, 'version', None)
if actual != expected:
raise ImportError(
'cannot import module %s.%s '
'(expected version: %d, actual: %r)'
% (pkgname, modname, expected, actual)
)
def importmod(modname):
"""Import module according to policy and check API version"""
try:
verpkg, purepkg = _packageprefs[policy]
except KeyError:
raise ImportError('invalid HGMODULEPOLICY %r' % policy)
assert verpkg or purepkg
if verpkg:
pn, mn = _modredirects.get((verpkg, modname), (verpkg, modname))
try:
mod = _importfrom(pn, mn)
if pn == verpkg:
_checkmod(pn, mn, mod)
return mod
except ImportError:
if not purepkg:
raise
pn, mn = _modredirects.get((purepkg, modname), (purepkg, modname))
return _importfrom(pn, mn)
def _isrustpermissive():
"""Assuming the policy is a Rust one, tell if it's permissive."""
return policy.endswith(b'-allow')
def importrust(modname, member=None, default=None):
"""Import Rust module according to policy and availability.
If policy isn't a Rust one, this returns `default`.
If either the module or its member is not available, this returns `default`
if policy is permissive and raises `ImportError` if not.
"""
if not policy.startswith(b'rust'):
return default
try:
mod = _importfrom('rustext', modname)
except ImportError:
if _isrustpermissive():
return default
raise
if member is None:
return mod
try:
return getattr(mod, member)
except AttributeError:
if _isrustpermissive():
return default
raise ImportError("Cannot import name %s" % member)