contrib/showstack.py

repo: look up nullrev context by revnum, not symbolic name

I think lookup of the 'null' symbol should be done via
scmutil.revsymbol() and repo['null'] is only supported for historical
reasons. However, repo[nullrev] is fine, so we can switch to that
instead of switching to scmutil.revsymbol('null').

Differential Revision: https://phab.mercurial-scm.org/D4780

# showstack.py - extension to dump a Python stack trace on signal
#
# binds to both SIGQUIT (Ctrl-\) and SIGINFO (Ctrl-T on BSDs)
"""dump stack trace when receiving SIGQUIT (Ctrl-\) and SIGINFO (Ctrl-T on BSDs)
"""

from __future__ import absolute_import
import signal
import sys
import traceback

def sigshow(*args):
    sys.stderr.write("\n")
    traceback.print_stack(args[1], limit=10, file=sys.stderr)
    sys.stderr.write("----\n")

def extsetup(ui):
    signal.signal(signal.SIGQUIT, sigshow)
    try:
        signal.signal(signal.SIGINFO, sigshow)
    except AttributeError:
        pass