tests/logexceptions.py

fix: highlight the required configuration and behavior of the fixer tools

The problem is that `hg help fix` didn't mention *how* to configure the tools,
and while I knew that `{rootpath}` existed in the configuration, I missed that
the tools require reading content from stdin.  (I configured `gofmt` to use
`{rootpath}`, and that had the effect of squashing all changes in a file at `.`
into the first commit and emptying that content from its descendants.)

Basically all this does is put a pointer in the default (command level) help to
the extension level help that mentions the configuration, and moves the
extension level help that documents reading from stdin and writing to stdout to
the top to give it more prominence.  The last sentence is adjusted a bit to
reflect the new location.

# logexceptions.py - Write files containing info about Mercurial exceptions
#
# Copyright 2017 Olivia Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.


import inspect
import os
import sys
import traceback
import uuid

from mercurial import (
    dispatch,
    extensions,
)


def handleexception(orig, ui):
    res = orig(ui)

    if not ui.environ.get(b'HGEXCEPTIONSDIR'):
        return res

    dest = os.path.join(
        ui.environ[b'HGEXCEPTIONSDIR'], str(uuid.uuid4()).encode('ascii')
    )

    exc_type, exc_value, exc_tb = sys.exc_info()

    stack = []
    tb = exc_tb
    while tb:
        stack.append(tb)
        tb = tb.tb_next
    stack.reverse()

    hgframe = 'unknown'
    hgline = 'unknown'

    # Find the first Mercurial frame in the stack.
    for tb in stack:
        mod = inspect.getmodule(tb)
        if not mod.__name__.startswith(('hg', 'mercurial')):
            continue

        frame = tb.tb_frame

        try:
            with open(inspect.getsourcefile(tb), 'r') as fh:
                hgline = fh.readlines()[frame.f_lineno - 1].strip()
        except (IndexError, OSError):
            pass

        hgframe = '%s:%d' % (frame.f_code.co_filename, frame.f_lineno)
        break

    primary = traceback.extract_tb(exc_tb)[-1]
    primaryframe = '%s:%d' % (primary.filename, primary.lineno)

    with open(dest, 'wb') as fh:
        parts = [
            str(exc_value),
            primaryframe,
            hgframe,
            hgline,
            ui.environ[b'TESTNAME'].decode('utf-8', 'replace'),
        ]
        fh.write(b'\0'.join(p.encode('utf-8', 'replace') for p in parts))


def extsetup(ui):
    extensions.wrapfunction(dispatch, 'handlecommandexception', handleexception)