procutil: make stdout line-buffered on Windows if connected to TTY Windows doesn’t support line buffering. Previously, we worked around that by setting the stream unbuffered. Instead, we can use our own line buffering we already use on Python 3.

procutil: split import and reassignment Besides making the code clearer, it will reduce the diff in the next patch.

procutil: move assignments closer to reassignments Doing reassignments is an anti-pattern IMHO, but I see how it makes sense here. When first looking at this code after jumping here with ctags, I missed the fact that stdout was reassigned. To make the code clearer, the assignments should be as close as possible to the reassignments.

procutil: factor out conditional creation of LineBufferedWrapper At the same time, document the logic and generalize it to work on all Python versions.

procutil: define LineBufferedWrapper on all Python versions There’s nothing Python 3-only about LineBufferedWrapper. In the future, we may want to use it on Windows, to work around missing line-buffering support.

tests: add tests for buffering behavior of mercurial.utils.procutil.stdout

cleanup: use slightly more meaningful name for temporary variable Not that it makes a big difference, but using `p` instead of `x` is clearer to me.

cleanup: use any() instead of checking truthiness of temporary list It was not immediately obvious to me, when first seeing this, why a list was created. It needed a second look to understand that the purpose was to check whether the condition is true for any of the parents. Using any() for that is clearer.

chg: suppress OSError in _restoreio() and add some logging (issue6330) According to issue6330, running chg on heavy loaded systems can lead to following error: ``` Traceback (most recent call last): File "path-to-hg/mercurial/commandserver.py", line 650, in _acceptnewconnection self._runworker(conn) File "path-to-hg/mercurial/commandserver.py", line 701, in _runworker prereposetups=[self._reposetup], File "path-to-hg/mercurial/commandserver.py", line 470, in _serverequest sv.cleanup() File "path-to-hg/mercurial/chgserver.py", line 381, in cleanup self._restoreio() File "path-to-hg/mercurial/chgserver.py", line 444, in _restoreio os.dup2(fd, fp.fileno()) OSError: [Errno 16] Device or resource busy ``` [man dup2] indicates that, on Linux, EBUSY comes from a race condition between open() and dup2(). However it's not clear why open() race occurred for newfd=stdin/out/err. We suppress the OSError in _restoreio() since the forked worker process will finish anyway and add some logging. Thanks to Mitchell Plamann for a detailed bug description and Yuya Nishihara for suggesting the fix.

py3: fix crash when server address is 0.0.0.0 (issue6362) `socket.getfqdn()` assumes that the name is passed as `str` on Python 3 and always returns `str` in this case. Mercurial passed `bytes` (but still expected a `str` result), which worked by chance in many cases, except for e.g. b'0.0.0.0', which was returned unchanged, breaking later code. Instead of calling `socket.getfqdn()`, we can also use `self.server_name` from the base `HTTPServer` class, which already stores the FQDN of the locally-bound socket name (see `BaseHTTPServer.py` in the Python 2 stdlib and `http/server.py` in the Python 3 stdlib).