hgeditor

tags-fnode-cache: do not repeatedly open the filelog in a loop

While getting multiple hgtagsfnodecache entries, we were opening (and closing)
the `.hgtags` filelog for each iteration. The meant repeatedly reading and
parsing the version same information from disk. A quite costly operation.

We no longer do this, leading to a sizable improvement in `hg debugupdatecache`
run for an already warm repositories.

### data-env-vars.name           = mercurial-2018-08-01-zstd-sparse-revlog
  # benchmark.name               = debug-update-cache
  # benchmark.variants.pre-state = warm
before:  1.711778 seconds
after:   0.213229 seconds  (-87.54%)
  # data-env-vars.name           = pypy-2018-08-01-zstd-sparse-revlog
before:  4.010817 seconds
after:   0.381141 seconds  (-90.50%)
  # data-env-vars.name           = netbeans-2018-08-01-zstd-sparse-revlog
before: 13.574141
after:   1.023007 seconds  (-92.46%)
  # data-env-vars.name           = mozilla-central-2018-08-01-zstd-sparse-revlog
before: 18.884656
after:   1.465735 seconds  (-92.24%)
  # data-env-vars.name           = mozilla-try-2019-02-18-zstd-sparse-revlog
before: 88.924823
after:   6.511771 seconds  (-92.68%)

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

# 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" HUP INT QUIT ABRT TERM

HGTMP=$(mktemp -d ${TMPDIR-/tmp}/hgeditor.XXXXXX)
[ x$HGTMP != x -a -d $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 $?