Re: [PATCH v2 2/2] rebase: Implement --merge via git-rebase--interactive
Hi Dscho,
On Mon, Nov 12, 2018 at 8:21 AM Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
Show 7 quoted lines
> > t3425: topology linearization was inconsistent across flavors of rebase,
> > as already noted in a TODO comment in the testcase. This was not
> > considered a bug before, so getting a different linearization due
> > to switching out backends should not be considered a bug now.
>
> Ideally, the test would be fixed, then. If it fails for other reasons than
> a real regression, it is not a very good regression test, is it.
I agree, it's not the best regression test. It'd be better if it defined and tested for "the correct behavior", but I suspect it has some value in that it's is guaranteeing that the rebase flavors at least give a "somewhat reasonable" result. Sadly, It just allowed all three rebase types to have slightly different "somewhat reasonable" answers.
Show 19 quoted lines
>
> > t5407: different rebase types varied slightly in how many times checkout
> > or commit or equivalents were called based on a quick comparison
> > of this tests and previous ones which covered different rebase
> > flavors. I think this is just attributable to this difference.
>
> This concerns me.
>
> In bigger repositories (no, I am not talking about Linux kernel sized
> ones, I consider those small-ish) there are a ton of files, and checkout
> and commit (and even more so reset) sadly do not have a runtime complexity
> growing with the number of modified files, but with the number of tracked
> files (and some commands even with the number of worktree files).
>
> So a larger number of commit/checkout operations makes me expect
> performance regressions.
>
> In this light, could you elaborate a bit on the differences you see
> between rebase -i and rebase -m?
I wrote this comment months ago and don't remember the full details. From the wording and as best I remember, I suspect I was at least partially annoyed by the fact that these and other regression tests for rebase seemed to not be testing for "correct" behavior, but "existing" behavior. That wouldn't be so bad, except that existing behavior differed on the exact same test setup for different rebase backends and the differences in behavior were checked and enforced in the regression tests. So, it became a matter of taste as to how much things should be made identical and to which backend, or whether it was more important to at least just consolidate the code first and keep the results at least reasonable. At the time, I figured getting fewer backends, all with reasonable behavior was a bit more important, but since this difference is worrisome to you, I will try to dig further into it.
Show 6 quoted lines
> > t9903: --merge uses the interactive backend so the prompt expected is
> > now REBASE-i.
>
> We should be able to make that test pass, still, by writing out a special
> file (e.g. $state_dir/opt_m) and testing for that. Users are oddly upset
> when their expectations are broken... (and I actually agree with them.)
I agree users are upset when expectations are broken, but why would they expect REBASE-m? In fact, I thought the prompt was a reflection of what backend was in use, so that if someone reported an issue to the git mailing list or a power user wanted to know where the control files were located, they could look for them. As such, I thought that switching the prompt to REBASE-i was the right thing to do so that it would match user expectations. Yes, the backend changed; that's part of the release notes.
Is there documentation somewhere that specifies the meaning of this prompt differently than the expectations I had somehow built up?
Show 19 quoted lines
> > diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
> > index 3407d835bd..35084f5681 100644
> > --- a/Documentation/git-rebase.txt
> > +++ b/Documentation/git-rebase.txt
> > @@ -504,15 +504,7 @@ See also INCOMPATIBLE OPTIONS below.
> > INCOMPATIBLE OPTIONS
> > --------------------
> >
> > -git-rebase has many flags that are incompatible with each other,
> > -predominantly due to the fact that it has three different underlying
> > -implementations:
> > -
> > - * one based on linkgit:git-am[1] (the default)
> > - * one based on git-merge-recursive (merge backend)
> > - * one based on linkgit:git-cherry-pick[1] (interactive backend)
> > -
>
> Could we retain this part, with `s/three/two/` and `/git-merge/d`? *Maybe*
> `s/interactive backend/interactive\/merge backend/`
Removing this was actually a suggestion by Phillip back in June at the end of https://public-inbox.org/git/13ccb4d9-582b-d26b-f595-59cb0b7037ab@talktalk.net/, for the purpose of removing an implementation details that users don't need to know about. As noted elsewhere in the thread, between you and Phillip, I'll add some comments to the commit message about this.
Show 9 quoted lines
> > -if test -n "$git_am_opt"; then
> > - incompatible_opts=$(echo " $git_am_opt " | \
> > - sed -e 's/ -q / /g' -e 's/^ \(.*\) $/\1/')
> > - if test -n "$interactive_rebase"
> > +incompatible_opts=$(echo " $git_am_opt " | \
> > + sed -e 's/ -q / /g' -e 's/^ \(.*\) $/\1/')
>
> Why are we no longer guarding this behind the condition that the user
> specified *any* option intended for the `am` backend?
The code is still correctly guarding, the diff is just confusing. Sorry about that. To explain, the code previously was basically:
if git_am_opt:
if interactive:
if incompatible_opts:
show_error_about_interactive_and_am_incompatibilities
if rebase-merge:
if incompatible_opts
show_error_about_merge_and_am_incompatibilitieswhich was a triply nested if, and the first (git_am_opt) and third (incompatible_opts) were slightly redundant; the latter being a subset of the former. Perhaps I should have done a separate cleanup patch before this that changed it to:
if incomptable_opts:
if interactive:
show_error_about_interactive_and_am_incompatibilities
if rebase-merge:
show_error_about_merge_and_am_incompatibilitiesBefore then having this patch coalesce that down to:
if incomptable_opts:
if interactive:
show_error_about_incompatible_optionsSince it tripped up both you and Phillip, I'll add this preliminary cleanup as a separate commit with accompanying explanation in my next re-roll.
Show 58 quoted lines
> > @@ -672,7 +664,7 @@ require_clean_work_tree "rebase" "$(gettext "Please commit or stash them.")"
> > # but this should be done only when upstream and onto are the same
> > # and if this is not an interactive rebase.
> > mb=$(git merge-base "$onto" "$orig_head")
> > -if test -z "$interactive_rebase" && test "$upstream" = "$onto" &&
> > +if test -z "$actually_interactive" && test "$upstream" = "$onto" &&
> > test "$mb" = "$onto" && test -z "$restrict_revision" &&
> > # linear history?
> > ! (git rev-list --parents "$onto".."$orig_head" | sane_grep " .* ") > /dev/null
> > @@ -716,6 +708,19 @@ then
> > GIT_PAGER='' git diff --stat --summary "$mb" "$onto"
> > fi
> >
> > +if test -z "$actually_interactive" && test "$mb" = "$orig_head"
> > +then
> > + # If the $onto is a proper descendant of the tip of the branch, then
> > + # we just fast-forwarded.
>
> This comment is misleading if it comes before, rather than after, the
> actual `checkout -q` command.
>
> > + say "$(eval_gettext "Fast-forwarded \$branch_name to \$onto_name.")"
> > + GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name" \
> > + git checkout -q "$onto^0" || die "could not detach HEAD"
> > + git update-ref ORIG_HEAD $orig_head
> > + move_to_original_branch
> > + finish_rebase
> > + exit 0
> > +fi
> > +
> > test -n "$interactive_rebase" && run_specific_rebase
> >
> > # Detach HEAD and reset the tree
> > @@ -725,16 +730,6 @@ GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name" \
> > git checkout -q "$onto^0" || die "could not detach HEAD"
> > git update-ref ORIG_HEAD $orig_head
>
> It is a pity that this hunk header hides the lines that you copied into
> the following conditional before moving it before the "if interactive, run
> it" line:
>
> >
> > -# If the $onto is a proper descendant of the tip of the branch, then
> > -# we just fast-forwarded.
> > -if test "$mb" = "$orig_head"
> > -then
> > - say "$(eval_gettext "Fast-forwarded \$branch_name to \$onto_name.")"
> > - move_to_original_branch
> > - finish_rebase
> > - exit 0
> > -fi
> > -
> > if test -n "$rebase_root"
> > then
> > revisions="$onto..$orig_head"
>
> What you did is correct, if duplicating code, and definitely the easiest
> way to do it. Just move the comment, and we're good here.
Show 6 quoted lines
>
> > diff --git a/git-rebase--merge.sh b/git-rebase--merge.sh
> > deleted file mode 100644
> > [... snip ...]
>
> Nice. Really nice!
Show 27 quoted lines
> > diff --git a/t/t3406-rebase-message.sh b/t/t3406-rebase-message.sh
> > index 0392e36d23..04d6c71899 100755
> > --- a/t/t3406-rebase-message.sh
> > +++ b/t/t3406-rebase-message.sh
> > @@ -17,14 +17,9 @@ test_expect_success 'setup' '
> > git tag start
> > '
> >
> > -cat >expect <<\EOF
> > -Already applied: 0001 A
> > -Already applied: 0002 B
> > -Committed: 0003 Z
> > -EOF
> > -
>
> As I had mentioned in the previous round: I think we can retain these
> messages for the `--merge` mode. And I think we should: users of --merge
> have most likely become to expect them.
>
> The most elegant way would probably be by adding code to the sequencer
> that outputs these lines if in "merge" mode (and add a flag to say that we
> *are* in "merge" mode).
>
> To that end, the `make_script()` function would not generate `# pick` but
> `drop` lines, I think, so that the sequencer can see those and print the
> `Already applied: <message>` lines. And a successful `TODO_PICK` would
> write out `Committed: <message>`.
I'll take a look, but is this a case where you want it only when rebase previously showed them, or should it also affect other cases such as --rebase-merges or --exec or general --interactive?
I'm hoping the latter, or that there's a good UI-level explanation for why certain rebase flags would actually mean that users should expect different output. rebase seems to be loaded with cases where slight variations on options yield very different side output and perhaps even results mostly based on which backend it historically was implemented on top of. Those gratuitous inconsistencies drive this particular user crazy.
Show 121 quoted lines
> > test_expect_success 'rebase -m' '
> > git rebase -m master >report &&
> > + >expect &&
> > sed -n -e "/^Already applied: /p" \
> > -e "/^Committed: /p" report >actual &&
> > test_cmp expect actual
> > diff --git a/t/t3420-rebase-autostash.sh b/t/t3420-rebase-autostash.sh
> > index f355c6825a..49077200c5 100755
> > --- a/t/t3420-rebase-autostash.sh
> > +++ b/t/t3420-rebase-autostash.sh
> > @@ -53,41 +53,6 @@ create_expected_success_interactive () {
> > EOF
> > }
> >
> > -create_expected_success_merge () {
> > - cat >expected <<-EOF
> > - $(grep "^Created autostash: [0-9a-f][0-9a-f]*\$" actual)
> > - HEAD is now at $(git rev-parse --short feature-branch) third commit
> > - First, rewinding head to replay your work on top of it...
> > - Merging unrelated-onto-branch with HEAD~1
> > - Merging:
> > - $(git rev-parse --short unrelated-onto-branch) unrelated commit
> > - $(git rev-parse --short feature-branch^) second commit
> > - found 1 common ancestor:
> > - $(git rev-parse --short feature-branch~2) initial commit
> > - [detached HEAD $(git rev-parse --short rebased-feature-branch~1)] second commit
> > - Author: A U Thor <author@example.com>
> > - Date: Thu Apr 7 15:14:13 2005 -0700
> > - 2 files changed, 2 insertions(+)
> > - create mode 100644 file1
> > - create mode 100644 file2
> > - Committed: 0001 second commit
> > - Merging unrelated-onto-branch with HEAD~0
> > - Merging:
> > - $(git rev-parse --short rebased-feature-branch~1) second commit
> > - $(git rev-parse --short feature-branch) third commit
> > - found 1 common ancestor:
> > - $(git rev-parse --short feature-branch~1) second commit
> > - [detached HEAD $(git rev-parse --short rebased-feature-branch)] third commit
> > - Author: A U Thor <author@example.com>
> > - Date: Thu Apr 7 15:15:13 2005 -0700
> > - 1 file changed, 1 insertion(+)
> > - create mode 100644 file3
> > - Committed: 0002 third commit
> > - All done.
> > - Applied autostash.
> > - EOF
> > -}
> > -
> > create_expected_failure_am () {
> > cat >expected <<-EOF
> > $(grep "^Created autostash: [0-9a-f][0-9a-f]*\$" actual)
> > @@ -112,43 +77,6 @@ create_expected_failure_interactive () {
> > EOF
> > }
> >
> > -create_expected_failure_merge () {
> > - cat >expected <<-EOF
> > - $(grep "^Created autostash: [0-9a-f][0-9a-f]*\$" actual)
> > - HEAD is now at $(git rev-parse --short feature-branch) third commit
> > - First, rewinding head to replay your work on top of it...
> > - Merging unrelated-onto-branch with HEAD~1
> > - Merging:
> > - $(git rev-parse --short unrelated-onto-branch) unrelated commit
> > - $(git rev-parse --short feature-branch^) second commit
> > - found 1 common ancestor:
> > - $(git rev-parse --short feature-branch~2) initial commit
> > - [detached HEAD $(git rev-parse --short rebased-feature-branch~1)] second commit
> > - Author: A U Thor <author@example.com>
> > - Date: Thu Apr 7 15:14:13 2005 -0700
> > - 2 files changed, 2 insertions(+)
> > - create mode 100644 file1
> > - create mode 100644 file2
> > - Committed: 0001 second commit
> > - Merging unrelated-onto-branch with HEAD~0
> > - Merging:
> > - $(git rev-parse --short rebased-feature-branch~1) second commit
> > - $(git rev-parse --short feature-branch) third commit
> > - found 1 common ancestor:
> > - $(git rev-parse --short feature-branch~1) second commit
> > - [detached HEAD $(git rev-parse --short rebased-feature-branch)] third commit
> > - Author: A U Thor <author@example.com>
> > - Date: Thu Apr 7 15:15:13 2005 -0700
> > - 1 file changed, 1 insertion(+)
> > - create mode 100644 file3
> > - Committed: 0002 third commit
> > - All done.
> > - Applying autostash resulted in conflicts.
> > - Your changes are safe in the stash.
> > - You can run "git stash pop" or "git stash drop" at any time.
> > - EOF
> > -}
> > -
> > testrebase () {
> > type=$1
> > dotest=$2
> > @@ -177,6 +105,9 @@ testrebase () {
> > test_expect_success "rebase$type --autostash: check output" '
> > test_when_finished git branch -D rebased-feature-branch &&
> > suffix=${type#\ --} && suffix=${suffix:-am} &&
> > + if test ${suffix} = "merge"; then
> > + suffix=interactive
> > + fi &&
> > create_expected_success_$suffix &&
> > test_i18ncmp expected actual
> > '
> > @@ -274,6 +205,9 @@ testrebase () {
> > test_expect_success "rebase$type: check output with conflicting stash" '
> > test_when_finished git branch -D rebased-feature-branch &&
> > suffix=${type#\ --} && suffix=${suffix:-am} &&
> > + if test ${suffix} = "merge"; then
> > + suffix=interactive
> > + fi &&
> > create_expected_failure_$suffix &&
> > test_i18ncmp expected actual
> > '
>
> As I stated earlier, I am uncomfortable with this solution. We change
> behavior rather noticeably, and the regression test tells us the same. We
> need to either try to deprecate `git rebase --merge`, or we need to at
> least attempt to recreate the old behavior with the sequencer.Yes, I understand not wanting to confuse users. But, serious question, are you (unintentionally) enforcing that we continue confusing users? I may be totally misunderstanding you or the problem space -- you know a lot more here than I do -- but to me your comments sound like enforcing bug compatibility over correctness.
As stated in the git-2.19 release notes (relative to my previous series),
"git rebase" behaved slightly differently depending on which one of
the three backends gets used; this has been documented and an
effort to make them more uniform has begun.
If we aren't trying to make the behavior more uniform and don't have
good UI rationale for things being different, then my motivation to
work on the affected aspects of rebase plummets.Perhaps this is attributable to a difference of worldview we have, or perhaps I'm just missing something totally obvious. I'm hoping it's the latter. But if it helps, here's the angle I viewed it from: These regression tests showed us that even when identical operations were being performed from the user perspective, we got very different results with the only difference being what backend happened to be selected (and the backends had significant overlap in the area they could all handle, as evidenced by the same testcase being run with each). That seems to me like pretty obvious proof that one or more backends was buggy. Said another way, it looks to me like this is another example of regression tests enforcing "one semi-reasonable behavior" instead of "the correct behavior".
I fully admit I don't have good UI rationale for why the output from the interactive backend is correct. It may not be. I also don't have good UI rationale for why the output from the traditional merge backend would be correct. (And it could be that both are wrong.) It'd be better to figure out what is correct and make the code and the tests implement and check for that. However, while I don't know what correct output to show the user is in these cases, I don't see how it's possible that both backends could have previously been correct. If someone could clearly enunciate a reason for different options to yield different output, I'd happily go and implement it. One obvious explanation could be "--interactive implies user-interactivity, which should thus have different output" -- but that doesn't explain the past because we have several interactive_rebase=implied cases which then should have matched --merge's output rather than --interactive's. Absent any such UI rationale, I'd rather at least make all the backends implement the same semi-reasonable behavior so it's at least consistent. Then when someone figures out what correct is, they can fix it all in one place.
I'm curious to hear if someone has a good reason for which messages should be preferred and when. I'm also curious if perhaps people think that I'm focusing too much on consistency and not enough on "backward compatibility".
Show 51 quoted lines
> > diff --git a/t/t3421-rebase-topology-linear.sh b/t/t3421-rebase-topology-linear.sh
> > index 99b2aac921..911ef49f70 100755
> > --- a/t/t3421-rebase-topology-linear.sh
> > +++ b/t/t3421-rebase-topology-linear.sh
> > @@ -111,7 +111,7 @@ test_run_rebase () {
> > "
> > }
> > test_run_rebase success ''
> > -test_run_rebase failure -m
> > +test_run_rebase success -m
> > test_run_rebase success -i
> > test_run_rebase success -p
> >
> > @@ -126,7 +126,7 @@ test_run_rebase () {
> > "
> > }
> > test_run_rebase success ''
> > -test_run_rebase failure -m
> > +test_run_rebase success -m
> > test_run_rebase success -i
> > test_run_rebase success -p
> >
> > @@ -141,7 +141,7 @@ test_run_rebase () {
> > "
> > }
> > test_run_rebase success ''
> > -test_run_rebase failure -m
> > +test_run_rebase success -m
> > test_run_rebase success -i
> > test_run_rebase success -p
> >
> > @@ -284,7 +284,7 @@ test_run_rebase () {
> > "
> > }
> > test_run_rebase success ''
> > -test_run_rebase failure -m
> > +test_run_rebase success -m
> > test_run_rebase success -i
> > test_run_rebase success -p
> >
> > @@ -315,7 +315,7 @@ test_run_rebase () {
> > "
> > }
> > test_run_rebase success ''
> > -test_run_rebase failure -m
> > +test_run_rebase success -m
> > test_run_rebase success -i
> > test_run_rebase failure -p
> >
>
> Nice.Show 53 quoted lines
> > diff --git a/t/t3425-rebase-topology-merges.sh b/t/t3425-rebase-topology-merges.sh
> > index 846f85c27e..cd505c0711 100755
> > --- a/t/t3425-rebase-topology-merges.sh
> > +++ b/t/t3425-rebase-topology-merges.sh
> > @@ -72,7 +72,7 @@ test_run_rebase () {
> > }
> > #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' -m
> > test_run_rebase success 'n o e' -i
> >
> > test_run_rebase () {
> > @@ -89,7 +89,7 @@ test_run_rebase () {
> > }
> > #TODO: make order consistent across all flavors of rebase
> > test_run_rebase success 'd e n o' ''
> > -test_run_rebase success 'd e n o' -m
> > +test_run_rebase success 'd n o e' -m
> > test_run_rebase success 'd n o e' -i
> >
> > test_run_rebase () {
> > @@ -106,7 +106,7 @@ test_run_rebase () {
> > }
> > #TODO: make order consistent across all flavors of rebase
> > test_run_rebase success 'd e n o' ''
> > -test_run_rebase success 'd e n o' -m
> > +test_run_rebase success 'd n o e' -m
> > test_run_rebase success 'd n o e' -i
> >
> > test_expect_success "rebase -p is no-op in non-linear history" "
>
> This is a bit unfortunate. I wonder if we could do something like this, to
> retain the current behavior:
>
> -- snip --
> diff --git a/sequencer.c b/sequencer.c
> index 9e1ab3a2a7..5018957e49 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -4394,7 +4394,8 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
> revs.reverse = 1;
> revs.right_only = 1;
> revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
> - revs.topo_order = 1;
> + if (!(flags & TODO_LIST_NO_TOPO_ORDER))
> + revs.topo_order = 1;
>
> revs.pretty_given = 1;
> git_config_get_string("rebase.instructionFormat", &format);
> -- snap -
>
> (and then pass TODO_LIST_NO_TOPO_ORDER if in "merge" mode)?Oh, sweet, we can make these consistent? I tried to look at this a little bit didn't dig too far. I love it; I'll definitely give it a try.
...but...why only in merge mode?? am, interactive, and merge backends gave different results, and the regression test even pointed out that whoever wrote these tests thought it was a bug (the several TODO comments). You knew where to fix it, but want to match previous behavior instead of fixing the inconsistency?
<Snipped a couple things that we already discussed since they were brought up in the commit message>
> Thank you for this pleasant read. I think there is still quite a bit of
> work to do, but you already did most of it.
Thanks for the detailed review and the pointers. Much appreciated. We may still have a disconnect of some sort (backwards/bug compatibility vs. correctness/consistency), or perhaps I'm just misunderstanding something for part of the review. However, I can definitely get to work on the other parts of your review comments, and hopefully we can talk through the other bits.
> Out of curiosity, do you have a public repository with these patches in a
> branch? (I might have an hour to play with it tonight...)
So, yesterday I pointed you at my rebase-new-default branch, but since it has other cruft as well, I just pushed this to a new branch with just the stuff in this patch series. I'll keep it up at
https://github.com/newren/git/tree/rebase-merge-on-sequencer
Thanks! Elijah
Elijah Newren
