contrib/showstack.py

run-tests: add --with-python3 to define a Python 3 interpreter

Currently, very few parts of Mercurial run under Python 3, notably the
test harness.

We want to write tests that run Python 3. For example, we want to
extend test-check-py3-compat.t to parse and load Python files.
However, we have a problem: finding appropriate files requires
running `hg files` and this requires Python 2 until `hg` works
with Python 3.

As a temporary workaround, we add --with-python3 to the test harness
to allow us to define the path to a Python 3 interpreter. This
interpreter is made available to the test environment via $PYTHON3 so
tests can run things with Python 3 while the test harness and `hg`
invocations continue to run from Python 2. To round out the feature,
a "py3exe" hghave check has been added.

# showstack.py - extension to dump a Python stack trace on signal
#
# binds to both 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