hgeditor

setup: refactor the version string to a subset of tag+tagdist-hash+date

Here is an array summarizing the mercurial version string:
      [A]       [B]   [C]           [D]
[1] clone      tag   clean  =>  tag
[2] clone      hash  clean  =>  latesttag+latesttagdistance-hash
[3] clone      tag   dirty  =>  tag+date
[4] clone      hash  dirty  =>  latesttag+latesttagdistance-hash+date
[5] archive    tag   clean  =>  tag
[6] archive    hash  clean  =>  latesttag+latesttagdistance-hash

Column [A]: Mercurial built from an hg *archive* or hg *clone* working directory
Column [B]: revision built has a *tag* or else default to the SHA1 *hash*
Column [C]: working tree *clean* or *dirty*
Column [D]: Mercurial version string

Over the previous version:
- row [5] did return just the node hash, now it returns the tag
- prepend the latest tag and the distance to it to rows [2][4][6]
- append also the date to row [3]; previously, it was just the tag
- the version string is with an empty string to avoid possible TypeError
  exceptions during string manipulations
- factorize the function to run hg commands; remove the error message as it is
  no more specific to the function.

This scheme enables to have first part of the version strings that can be
compared, whether it has been built from a tagged or untagged revision.
The second part of the version adds a hash for untagged revisions and today's
date if the working tree has local modifications.
As the version string does not contain spaces or special characters, it should
not break script parsing the 'hg version' command and should be usable for use
in file names.

The new code also ensure that the version string has exactly the same version
string, whether it has been built from an archive or from a clone.

#!/bin/sh
#
# This is an example of using HGEDITOR to create of diff to review the
# changes while commiting.

# If you want to pass your favourite editor some other parameters
# only for Mercurial, modify this:
case "${EDITOR}" in
    "")
        EDITOR="vi"
        ;;
    emacs)
        EDITOR="$EDITOR -nw"
        ;;
    gvim|vim)
        EDITOR="$EDITOR -f -o"
        ;;
esac


HGTMP=""
cleanup_exit() {
    rm -rf "$HGTMP"
}

# Remove temporary files even if we get interrupted
trap "cleanup_exit" 0 # normal exit
trap "exit 255" 1 2 3 6 15 # HUP INT QUIT ABRT TERM

HGTMP="${TMPDIR-/tmp}/hgeditor.$RANDOM.$RANDOM.$RANDOM.$$"
(umask 077 && mkdir "$HGTMP") || {
    echo "Could not create temporary directory! Exiting." 1>&2
    exit 1
}

(
    grep '^HG: changed' "$1" | cut -b 13- | while read changed; do
        "$HG" diff "$changed" >> "$HGTMP/diff"
    done
)

cat "$1" > "$HGTMP/msg"

MD5=$(which md5sum 2>/dev/null) || \
    MD5=$(which md5 2>/dev/null)
[ -x "${MD5}" ] && CHECKSUM=`${MD5} "$HGTMP/msg"`
if [ -s "$HGTMP/diff" ]; then
    $EDITOR "$HGTMP/msg" "$HGTMP/diff" || exit $?
else
    $EDITOR "$HGTMP/msg" || exit $?
fi
[ -x "${MD5}" ] && (echo "$CHECKSUM" | ${MD5} -c >/dev/null 2>&1 && exit 13)

mv "$HGTMP/msg" "$1"

exit $?