git/git-rebase--merge.sh
Elijah Newren c91c944a06 rebase: define linearization ordering and enforce it
Ever since commit 3f213981e4 ("add tests for rebasing merged history",
2013-06-06), t3425 has had tests which included the rebasing of merged
history and whose order of applied commits was checked.  Unfortunately,
the tests expected different behavior depending on which backend was in
use.  Implementing these checks was the following four lines (including
the TODO message) which were repeated verbatim three times in t3425:

    #TODO: make order consistent across all flavors of rebase
    test_run_rebase success 'e n o' ''
    test_run_rebase success 'e n o' -m
    test_run_rebase success 'n o e' -i

As part of the effort to reduce differences between the rebase backends
so that users get more uniform behavior, let's define the correct
behavior and modify the different backends so they all get the right
answer.  It turns out that the difference in behavior here is entirely
due to topological sorting; since some backends require topological
sorting (particularly when --rebase-merges is specified), require it for
all modes.  Modify the am and merge backends to implement this.

Performance Considerations:

I was unable to measure any appreciable performance difference with this
change.  Trying to control the run-to-run variation was difficult; I
eventually found a headless beefy box that I could ssh into, which
seemed to help.  Using git.git, I ran the following testcase:
    $ git reset --hard v2.20.0-rc1~2
    $ time git rebase --quiet v2.20.0-rc0~16

I first ran once to warm any disk caches, then ran five subsequent runs
and recorded the times of those five.  I observed the following results
for the average time:

     Before this change:
       "real" timing: 1.340s (standard deviation: 0.040s)
       "user" timing: 1.050s (standard deviation: 0.041s)
       "sys"  timing: 0.270s (standard deviation: 0.011s)
     After  this change:
       "real" timing: 1.327s (standard deviation: 0.065s)
       "user" timing: 1.031s (standard deviation: 0.061s)
       "sys"  timing: 0.280s (standard deviation: 0.014s)

Measurements aside, I would expect the timing for walking revisions to
be dwarfed by the work involved in creating and applying patches, so
this isn't too surprising.  Further, while somewhat counter-intuitive,
it is possible that turning on topological sorting is actually a
performance improvement: by way of comparison, turning on --topo-order
made fast-export faster (see
https://public-inbox.org/git/20090211135640.GA19600@coredump.intra.peff.net/).

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-12-28 12:49:48 -08:00

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# This shell script fragment is sourced by git-rebase to implement
# its merge-based non-interactive mode that copes well with renamed
# files.
#
# Copyright (c) 2010 Junio C Hamano.
#
prec=4
read_state () {
onto_name=$(cat "$state_dir"/onto_name) &&
end=$(cat "$state_dir"/end) &&
msgnum=$(cat "$state_dir"/msgnum)
}
continue_merge () {
test -d "$state_dir" || die "$state_dir directory does not exist"
unmerged=$(git ls-files -u)
if test -n "$unmerged"
then
echo "You still have unmerged paths in your index"
echo "did you forget to use git add?"
die "$resolvemsg"
fi
cmt=$(cat "$state_dir/current")
if ! git diff-index --quiet --ignore-submodules HEAD --
then
if ! git commit ${gpg_sign_opt:+"$gpg_sign_opt"} $signoff $allow_empty_message \
--no-verify -C "$cmt"
then
echo "Commit failed, please do not call \"git commit\""
echo "directly, but instead do one of the following: "
die "$resolvemsg"
fi
if test -z "$GIT_QUIET"
then
printf "Committed: %0${prec}d " $msgnum
fi
echo "$cmt $(git rev-parse HEAD^0)" >> "$state_dir/rewritten"
else
if test -z "$GIT_QUIET"
then
printf "Already applied: %0${prec}d " $msgnum
fi
fi
test -z "$GIT_QUIET" &&
GIT_PAGER='' git log --format=%s -1 "$cmt"
# onto the next patch:
msgnum=$(($msgnum + 1))
echo "$msgnum" >"$state_dir/msgnum"
}
call_merge () {
msgnum="$1"
echo "$msgnum" >"$state_dir/msgnum"
cmt="$(cat "$state_dir/cmt.$msgnum")"
echo "$cmt" > "$state_dir/current"
git update-ref REBASE_HEAD "$cmt"
hd=$(git rev-parse --verify HEAD)
cmt_name=$(git symbolic-ref HEAD 2> /dev/null || echo HEAD)
eval GITHEAD_$cmt='"${cmt_name##refs/heads/}~$(($end - $msgnum))"'
eval GITHEAD_$hd='$onto_name'
export GITHEAD_$cmt GITHEAD_$hd
if test -n "$GIT_QUIET"
then
GIT_MERGE_VERBOSITY=1 && export GIT_MERGE_VERBOSITY
fi
test -z "$strategy" && strategy=recursive
# If cmt doesn't have a parent, don't include it as a base
base=$(git rev-parse --verify --quiet $cmt^)
eval 'git merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
rv=$?
case "$rv" in
0)
unset GITHEAD_$cmt GITHEAD_$hd
return
;;
1)
git rerere $allow_rerere_autoupdate
die "$resolvemsg"
;;
2)
echo "Strategy: $strategy failed, try another" 1>&2
die "$resolvemsg"
;;
*)
die "Unknown exit code ($rv) from command:" \
"git merge-$strategy $cmt^ -- HEAD $cmt"
;;
esac
}
finish_rb_merge () {
move_to_original_branch
if test -s "$state_dir"/rewritten
then
git notes copy --for-rewrite=rebase <"$state_dir"/rewritten
hook="$(git rev-parse --git-path hooks/post-rewrite)"
test -x "$hook" && "$hook" rebase <"$state_dir"/rewritten
fi
say All done.
}
git_rebase__merge () {
case "$action" in
continue)
read_state
continue_merge
while test "$msgnum" -le "$end"
do
call_merge "$msgnum"
continue_merge
done
finish_rb_merge
return
;;
skip)
read_state
git rerere clear
cmt="$(cat "$state_dir/cmt.$msgnum")"
echo "$cmt $(git rev-parse HEAD^0)" >> "$state_dir/rewritten"
msgnum=$(($msgnum + 1))
while test "$msgnum" -le "$end"
do
call_merge "$msgnum"
continue_merge
done
finish_rb_merge
return
;;
show-current-patch)
exec git show REBASE_HEAD --
;;
esac
mkdir -p "$state_dir"
echo "$onto_name" > "$state_dir/onto_name"
write_basic_state
rm -f "$(git rev-parse --git-path REBASE_HEAD)"
msgnum=0
for cmt in $(git rev-list --topo-order --reverse --no-merges "$revisions")
do
msgnum=$(($msgnum + 1))
echo "$cmt" > "$state_dir/cmt.$msgnum"
done
echo 1 >"$state_dir/msgnum"
echo $msgnum >"$state_dir/end"
end=$msgnum
msgnum=1
while test "$msgnum" -le "$end"
do
call_merge "$msgnum"
continue_merge
done
finish_rb_merge
}