From: Elijah Newren <newren@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>,
Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH 2/2] merge: avoid searching for strategies with fewer than 0 conflicts
Date: Mon, 22 Aug 2022 08:00:00 -0700 [thread overview]
Message-ID: <CABPp-BHy-Xs0S1-9kL7X4mi6JNfd420-vpVsswXNuXsc5C7AtA@mail.gmail.com> (raw)
In-Reply-To: <xmqqwnb1fp5n.fsf@gitster.g>
On Sun, Aug 21, 2022 at 11:05 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> "Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: Elijah Newren <newren@gmail.com>
> >
> > builtin/merge.c has a loop over the specified strategies, where if
> > they all fail with conflicts, it picks the one with the least number
> > of conflicts.
> >
> > In the codepath that finds a successful merge, if an automatic commit
> > was wanted, the code breaks out of the above loop, which makes sense.
> > However, if the user requested there be no automatic commit, the loop
> > would continue looking for a "better" strategy. Since it had just
> > found a strategy with 0 conflicts though, and it is not possible to
> > have fewer than 0 conflicts, the continuing search is guaranteed to be
> > futile.
>
> Let's imagine "git merge -s ours -s ort X", both of which resolve
> the merge cleanly but differently.
>
> The "best_cnt" thing tries to find the last strategy with the lowest
> score from evaluate_result(), so strictly speaking I think this
> changes the behaviour. Am I mistaken?
Yes, you are.
Though, to be fair, my commit message is wrong too.
I'll explain below...
> When two strategies 'ours' and 'ort' resolved a given merge cleanly
> (but differently), we would have taken the result from 'ort' in the
> original code, but now we stop at seeing that 'ours' resolved the
> merge cleanly and use its result.
>
> > cnt = (use_strategies_nr > 1) ? evaluate_result() : 0;
> > if (best_cnt <= 0 || cnt <= best_cnt) {
No, the original code would not have taken 'ort'. You have overlooked
the part of the code immediately above these two lines:
if (ret < 2) {
if (!ret) {
if (option_commit) {
/* Automerge succeeded. */
automerge_was_ok = 1;
break;
}
merge_was_ok = 1;
}
In particular, the "break" is key. If the first strategy succeeds
(and the user did not specify --no-commit), then the loop will hit
that break statement and bail out of the loop, preventing any other
merge strategy from being tried. In contrast, if the user did specify
--no-commit and the previous strategy succeeded, then we will continue
the loop. That seems rather inconsistent, since --no-commit should
not affect the choice of strategy.
However, I missed two things in my reading. You are correct that I
missed the "<=" as opposed to "<" when I wrote my commit message,
though that turns out to not matter much due to the second thing. The
second thing I missed was part of the code at the beginning of the
loop:
for (i = 0; !merge_was_ok && i < use_strategies_nr; i++) {
In particular, that "!merge_was_ok" check means that the code would
bail early whenever ret was 0, regardless of whether --no-commit was
passed. So, my code turns out to not only leave behavior alone, but
also doesn't count as an optimization either -- it's simply a
half-baked cleanup. If I also get rid of the now-redundant
"!merge_was_ok" check in the for loop and fix my commit message, then
I think it'd be a fully-baked code cleanup.
I'll submit an update.
next prev parent reply other threads:[~2022-08-22 15:01 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-21 4:38 [PATCH 0/2] Miscellaneous merge fixes Elijah Newren via GitGitGadget
2022-08-21 4:38 ` [PATCH 1/2] merge: only apply autostash when appropriate Elijah Newren via GitGitGadget
2022-08-21 4:52 ` Eric Sunshine
2022-08-21 5:18 ` Elijah Newren
2022-08-21 4:38 ` [PATCH 2/2] merge: avoid searching for strategies with fewer than 0 conflicts Elijah Newren via GitGitGadget
2022-08-21 18:05 ` Junio C Hamano
2022-08-22 15:00 ` Elijah Newren [this message]
2022-08-22 16:19 ` Junio C Hamano
2022-08-23 1:18 ` Elijah Newren
2022-08-23 2:42 ` [PATCH v2 0/3] Miscellaneous merge fixes Elijah Newren via GitGitGadget
2022-08-23 2:42 ` [PATCH v2 1/3] merge: only apply autostash when appropriate Elijah Newren via GitGitGadget
2022-08-23 2:42 ` [PATCH v2 2/3] merge: cleanup confusing logic for handling successful merges Elijah Newren via GitGitGadget
2022-08-23 2:42 ` [PATCH v2 3/3] merge: small code readability improvement Elijah Newren via GitGitGadget
2022-08-23 3:03 ` [PATCH v2 0/3] Miscellaneous merge fixes Elijah Newren
2022-08-24 21:09 ` Junio C Hamano
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CABPp-BHy-Xs0S1-9kL7X4mi6JNfd420-vpVsswXNuXsc5C7AtA@mail.gmail.com \
--to=newren@gmail.com \
--cc=git@vger.kernel.org \
--cc=gitgitgadget@gmail.com \
--cc=gitster@pobox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).