hgdemandimport/tracing.py

node: stop converting binascii.Error to TypeError in bin()

Changeset f574cc00831a introduced the wrapper, to make bin() behave like on
Python 2, where it raised TypeError in many cases. Another previous approach,
changing callers to catch binascii.Error in addition to TypeError, was backed
out after negative review feedback [1].

However, I think it’s worth reconsidering the approach. Now that we’re on
Python 3 only, callers have to catch only binascii.Error instead of both.
Catching binascii.Error instead of TypeError has the advantage that it’s less
likely to cover a programming error (e.g. passing an int to bin() raises
TypeError). Also, raising TypeError never made sense semantically when bin()
got an argument of valid type.

As a side-effect, this fixed an exception in test-http-bad-server.t. The TODO
was outdated: it was not an uncaught ValueError in batch.results() but uncaught
TypeError from the now removed wrapper. Now that bin() raises binascii.Error
instead of TypeError, it gets converted to a proper error in
wirepeer.heads.<locals>.decode() that catches ValueError (superclass of
binascii.Error). This is a good example of why this changeset is a good idea.
Catching TypeError instead of ValueError there would not make much sense.

[1] https://phab.mercurial-scm.org/D2244

# Support code for event tracing in Mercurial. Lives in demandimport
# so it can also be used in demandimport.
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import contextlib
import os

_pipe = None
_checked = False
_session = 'none'


def _isactive():
    global _pipe, _session, _checked
    if _pipe is None:
        if _checked:
            return False
        _checked = True
        if 'HGCATAPULTSERVERPIPE' not in os.environ:
            return False
        _pipe = open(os.environ['HGCATAPULTSERVERPIPE'], 'w', 1)
        _session = os.environ.get('HGCATAPULTSESSION', 'none')
    return True


@contextlib.contextmanager
def log(whencefmt, *whenceargs):
    if not _isactive():
        yield
        return
    whence = whencefmt % whenceargs
    try:
        # Both writes to the pipe are wrapped in try/except to ignore
        # errors, as we can see mysterious errors in here if the pager
        # is active. Presumably other conditions could trigger
        # problems too.
        try:
            _pipe.write('START %s %s\n' % (_session, whence))
        except IOError:
            pass
        yield
    finally:
        try:
            _pipe.write('END %s %s\n' % (_session, whence))
        except IOError:
            pass


def counter(label, amount, *labelargs):
    if not _isactive():
        return
    l = label % labelargs
    # See above in log() for why this is in a try/except.
    try:
        _pipe.write('COUNTER %s %d %s\n' % (_session, amount, l))
    except IOError:
        pass