view contrib/editmerge @ 20155:21dafd8546d1

parsers: fail fast if Python has wrong minor version (issue4110)

This change causes an informative ImportError to be raised when importing
the extension module parsers if the minor version of the currently-running
Python interpreter doesn't match that of the Python that was used when
compiling the extension module.  Here is an example of what the new error
looks like:

  Traceback (most recent call last):
    File "test.py", line 1, in <module>
      import mercurial.parsers
  ImportError: Python minor version mismatch: The Mercurial extension
  modules were compiled with Python 2.7.6, but Mercurial is currently using
  Python with sys.hexversion=33883888: Python 2.5.6
  (r256:88840, Nov 18 2012, 05:37:10)
  [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))]
   at: /opt/local/Library/Frameworks/Python.framework/Versions/2.5/Resources/
    Python.app/Contents/MacOS/Python

The reason for raising an error in this scenario is that Python's C API
is known not to be compatible from minor version to minor version, even
if sys.api_version is the same.  See for example this Python bug report
about incompatibilities between 2.5 and 2.6+:

  http://bugs.python.org/issue8118

These incompatibilities can cause Mercurial to break in mysterious,
unforeseen ways.  For example, when Mercurial compiled with Python 2.7 was
run with 2.5, the following crash occurred when running "hg status":

  http://bz.selenic.com/show_bug.cgi?id=4110

After this crash was fixed, running with Python 2.5 no longer crashes, but
the following puzzling behavior still occurs:

    $ hg status
      ...
      File ".../mercurial/changelog.py", line 123, in __init__
        revlog.revlog.__init__(self, opener, "00changelog.i")
      File ".../mercurial/revlog.py", line 251, in __init__
        d = self._io.parseindex(i, self._inline)
      File ".../mercurial/revlog.py", line 158, in parseindex
        index, cache = parsers.parse_index2(data, inline)
    TypeError: data is not a string

which can be reproduced more simply with:

    import mercurial.parsers as parsers
    parsers.parse_index2("", True)

Both the crash and the TypeError occurred because the Python C API's
PyString_Check returns the wrong value when the C header files from
Python 2.7 are run with Python 2.5.  This is an example of an
incompatibility of the sort mentioned in the Python bug report above.

Failing fast with an informative error message will result in a better
user experience in cases like the above.  The information in the ImportError
will also simplify troubleshooting for those on Mercurial mailing lists,
the bug tracker, etc.

This patch only adds the version check to parsers.c, which is sufficient
to affect command-line commands like "hg status" and "hg summary".
An idea for a future improvement is to move the version-checking C code
to a more central location, and have it run when importing all
Mercurial extension modules and not just parsers.c.

#!/bin/bash
# A simple script for opening merge conflicts in the editor.
# Use the following Mercurial settings to enable it.
#
# [ui]
# merge = editmerge
#
# [merge-tools]
# editmerge.args=$output
# editmerge.check=changed
# editmerge.premerge=keep

FILE=$1

getlines() {
  grep -n "<<<<<<" $FILE | cut -f1 -d:
}

# editor preference loosely based on http://mercurial.selenic.com/wiki/editor
# hg showconfig is at the bottom though, since it's slow to run (0.15 seconds)
ED=$HGEDITOR
if [ "$ED" = "" ] ; then
  ED=$VISUAL
fi
if [ "$ED" = "" ] ; then
  ED=$EDITOR
fi
if [ "$ED" = "" ] ; then
  ED=$(hg showconfig ui.editor)
fi
if [ "$ED" = "" ] ; then
  echo "merge failed - unable to find editor"
  exit 1
fi

if [ "$ED" = "emacs" ] || [ "$ED" = "nano" ] || [ "$ED" = "vim" ] ; then
  FIRSTLINE=$(getlines | head -n 1)
  PREVIOUSLINE=""

  # open the editor to the first conflict until there are no more
  # or the user stops editing the file
  while [ ! "$FIRSTLINE" = "" ] && [ ! "$FIRSTLINE" = "$PREVIOUSLINE" ] ; do
    $ED +$FIRSTLINE $FILE
    PREVIOUSLINE=$FIRSTLINE
    FIRSTLINE=$(getlines | head -n 1)
  done
else
  $ED $FILE
fi

# get the line numbers of the remaining conflicts
CONFLICTS=$(getlines | sed ':a;N;$!ba;s/\n/, /g')
if [ ! "$CONFLICTS" = "" ] ; then
  echo "merge failed - resolve the conflicts (line $CONFLICTS) then use 'hg resolve --mark'"
  exit 1
fi

exit 0