Hi Alex

On 12/03/2023 20:57, Alex Henrie wrote:

On Tue, Mar 7, 2023 at 9:23 AM Phillip Wood [off-list ref] wrote:

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On 04/03/2023 23:24, Alex Henrie wrote:

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On Thu, Mar 2, 2023 at 2:37 AM Phillip Wood [off-list ref] wrote:

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On 25/02/2023 18:03, Alex Henrie wrote:

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+rebase.merges::
+     Whether and how to set the `--rebase-merges` option by default. Can
+     be `rebase-cousins`, `no-rebase-cousins`, or a boolean. Setting to
+     true is equivalent to `--rebase-merges` without an argument, setting to
+     `rebase-cousins` or `no-rebase-cousins` is equivalent to
+     `--rebase-merges` with that value as its argument, and setting to false
+     is equivalent to `--no-rebase-merges`. Passing `--rebase-merges` on the
+     command line without an argument overrides a `rebase.merges=false`
+     configuration but does not override other values of `rebase.merge`.

I'm still not clear why the commandline doesn't override the config in
all cases as is our usual practice. After all if the user has set
rebase.merges then they don't need to pass --rebase-merges unless they
want to override the config.

Given the current push to turn rebase-merges on by default, it seems
likely that rebase-cousins will also be turned on by default at some
point after that.

It is good to try and future proof things but this seems rather
hypothetical. I don't really see how the choice of whether
--rebase-merges is turned on by default is related to the choice of
whether or not to rebase cousins by default. It is worth noting that the
default was changed to from rebase-cousins to no-rebase-cousins early in
the development of --rebase-merges[1] as it was felt to be less surprising.

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[1]
https://lore.kernel.org/git/nycvar.QRO.7.76.6.1801292251240.35@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz/ (local)

Thank you for sharing that link. Even though I got the tests right, I
got confused and started thinking that rebase-cousins was a more
thorough version of rebase-merges. In fact, they do opposite things:
rebase-merges tries to preserve the graph and rebase-cousins
intentionally restructures the graph. In my opinion using the word
"rebase" in the names of both options was another unfortunate UI
decision, but I understand the difference now.

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There will be a warning about the default changing,
and we'll want to let users suppress that warning by setting
rebase.rebaseMerges=rebase-cousins. It would then be very confusing if
a --rebase-merges from some old alias continued to mean
--rebase-merges=no-rebase-cousins when the user expects it to start
behaving as though the default has already changed.

But aren't you breaking those aliases now when
rebase.rebaseMerges=rebase-cousins? That's what I'm objecting to. It
seems like we're breaking things now to avoid a hypothetical future
change breaking them which does not seem like the right trade off to me.

It also does not fit with the way other optional arguments interact with
their associated config setting. For example "git branch/checkout/switch
--track" and branch.autoSetupMerge. If the optional argument to --track
is omitted it defaults to "direct" irrespective of the config.

 >

What I really don't want is to paint ourselves into a corner.

Nor do I but we already seem to be in some kind of corner as what you're 
proposing breaks the status quo and the existing convention that command 
line options override config settings.

You're
right that it's unlikely that the default will ever change from
no-rebase-cousins to rebase-cousins; I was mistaken. However, Glen
thinks that in the future we might have some kind of
rebase-evil-merges mode as well, and that that might become the
default. If we don't let the rebase.rebaseMerges config value control
the default behavior of --rebase-merges without an argument on the
command line, we would have to introduce a separate config option for
the transition, which would be ugly.

I'm optimistic that Elijah's work on rebasing evil merges will allow us 
to improve --rebase-merges. I expect that we'll enable it by default 
once it is merged. I do not think that we should add another argument 
for --rebase-merges to disable it though as that would be orthogonal to 
"rebase-cousins" and "no-rebase-cousins" which control what commits get 
rebased not how merges are rebased. If users want to disable the better 
rebasing of merges we'll need to add a --remerge option or something 
like that.

More voices would be helpful here. Does anyone else have an opinion on
how likely it is that the default rebase-merges mode will change in
the future? Or on whether rebase.rebaseMerges should be allowed to
affect --rebase-merges in order to facilitate such a change?

Getting other's views would indeed be helpful

Best Wishes

Phillip

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+test_expect_success '--rebase-merges overrides rebase.merges=false' '
+     test_config rebase.merges false &&
+     git checkout -b override-config-merges-false E &&
+     before="$(git rev-parse --verify HEAD)" &&
+     test_tick &&
+     git rebase --rebase-merges C &&
+     test_cmp_rev HEAD $before

This test passes if the rebase does nothing, maybe pass --force and
check the graph?

The rebase is supposed to do nothing here.

It's not doing nothing though - it is rebasing the branch, it just
happens that everything fast-forwards so HEAD ends up unchanged. My
point is that this test should verify the branch has been rebased. Maybe
you could check the reflog message for HEAD@{0} is

         rebase (finish): returning to refs/heads/override-config-merges-false

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Checking that the commit
hash is the same is just a quick way to check that the entire graph is
the same. What more would be checked by checking the graph instead of
the hash?

By using --force and checking the graph you check that the rebase
actually happened.

I got the impression that people like that not checking the graph
itself (or the reflog) makes the tests more concise, but I don't care
much either way. For what it's worth, the way I did it matches the
existing tests in the file. If you can find at least one other person
who thinks that it ought to change for this patch series to be
accepted, and no one else objects, I'll change it.

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Thanks for working on this

You're welcome; hopefully we can get the remaining details ironed out quickly.

-Alex