rebase -r: support merge strategies other than recursive

[dscho]

This is the most notable shortcoming that --rebase-merges has, still, relative to --preserve-merges' capabilities: it does not support passing custom merge strategies or custom merge strategy options.

Let's fix this.

While working on this patch series, of course I tried to copy-edit the test cases we have, to cover --preserve-merges' support for merge strategies. Oh my, did I regret this decision as soon as my eyes set sight on t3427-rebase-subtree.sh!

At first I tried my best to make heads or tails of t3427, for way too long. In the end the only way to understand what the heck it tries to do was to actually fix it. That's why this patch series looks as if it focuses on t3427 rather than on adding support for custom merge strategies to the --rebase-merges mode.

As a consolation to myself, this work was actually worth it, surprising as that may look. Not only is t3427 now really easy to understand, adding that test case for --rebase-merges -Xsubtree tickled the sequencer enough to reveal a long-standing bug: the --onto option was simply ignored when passed together with --rebase-merges and --root. For good measure, this patch series addresses this bug, too.

Changes since v1:

• Rebased to the current js/rebase-cleanup: that branch itself was rebased, and as a consequence, one already-applied patch was dropped from this patch series.
• Forward-fixed the fakesha handling, just in case that anybody wants to use it with a regular pick command in the future (thanks, brian).

Cc: brian m. carlson sandals@crustytoothpaste.net

[dscho]

/submit

[gitgitgadget]

Submitted as pull.294.git.gitgitgadget@gmail.com

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This branch is now known as js/rebase-r-strategy.

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On the Git mailing list, Elijah Newren wrote (reply to this):

fast-export and fast-import can easily handle the simple rewrite that
was being done by filter-branch, and should be faster on systems with a
slow fork.  Measuring the overall time taken for all of t3427 (not just
the difference between filter-branch and fast-export/fast-import) shows
a speedup of about 5% on Linux and 11% on Mac.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
This patch is meant to be added onto the end of js/rebase-r-strategy; an
earlier version of this patch conflicted js/rebase-r-strategy so now I'm
basing on top of that series.  The speedup is also less impressive now
that there is only one filter-branch invocation being replaced instead of
a handful.  Still a nice speedup, though.

 t/t3427-rebase-subtree.sh | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/t/t3427-rebase-subtree.sh b/t/t3427-rebase-subtree.sh
index 39e348de16..bec48e6a1f 100755
--- a/t/t3427-rebase-subtree.sh
+++ b/t/t3427-rebase-subtree.sh
@@ -59,7 +59,10 @@ test_expect_success 'setup' '
 	test_commit files_subtree/master5 &&
 
 	git checkout -b to-rebase &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
+	git fast-export --no-data HEAD -- files_subtree/ |
+		sed -e "s%\([0-9a-f]\{40\} \)files_subtree/%\1%" |
+		git fast-import --force --quiet &&
+	git reset --hard &&
 	git commit -m "Empty commit" --allow-empty
 '
 
-- 
2.22.0.19.ga495766805

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On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Elijah,

On Wed, 4 Sep 2019, Elijah Newren wrote:

> fast-export and fast-import can easily handle the simple rewrite that
> was being done by filter-branch, and should be faster on systems with a
> slow fork.  Measuring the overall time taken for all of t3427 (not just
> the difference between filter-branch and fast-export/fast-import) shows
> a speedup of about 5% on Linux and 11% on Mac.
>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
> This patch is meant to be added onto the end of js/rebase-r-strategy; an
> earlier version of this patch conflicted js/rebase-r-strategy so now I'm
> basing on top of that series.  The speedup is also less impressive now
> that there is only one filter-branch invocation being replaced instead o=
f
> a handful.  Still a nice speedup, though.

ACK!

Thanks,
Dscho

>
>  t/t3427-rebase-subtree.sh | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/t/t3427-rebase-subtree.sh b/t/t3427-rebase-subtree.sh
> index 39e348de16..bec48e6a1f 100755
> --- a/t/t3427-rebase-subtree.sh
> +++ b/t/t3427-rebase-subtree.sh
> @@ -59,7 +59,10 @@ test_expect_success 'setup' '
>  	test_commit files_subtree/master5 &&
>
>  	git checkout -b to-rebase &&
> -	git filter-branch --prune-empty -f --subdirectory-filter files_subtree=
 &&
> +	git fast-export --no-data HEAD -- files_subtree/ |
> +		sed -e "s%\([0-9a-f]\{40\} \)files_subtree/%\1%" |
> +		git fast-import --force --quiet &&
> +	git reset --hard &&
>  	git commit -m "Empty commit" --allow-empty
>  '
>
> --
> 2.22.0.19.ga495766805
>
>

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This patch series was integrated into pu via git@4537165.

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On the Git mailing list, Junio C Hamano wrote (reply to this):

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> Hi Elijah,
>
> On Wed, 4 Sep 2019, Elijah Newren wrote:
>
>> fast-export and fast-import can easily handle the simple rewrite that
>> was being done by filter-branch, and should be faster on systems with a
>> slow fork.  Measuring the overall time taken for all of t3427 (not just
>> the difference between filter-branch and fast-export/fast-import) shows
>> a speedup of about 5% on Linux and 11% on Mac.
>>
>> Signed-off-by: Elijah Newren <newren@gmail.com>
>> ---
>> This patch is meant to be added onto the end of js/rebase-r-strategy; an
>> earlier version of this patch conflicted js/rebase-r-strategy so now I'm
>> basing on top of that series.  The speedup is also less impressive now
>> that there is only one filter-branch invocation being replaced instead of
>> a handful.  Still a nice speedup, though.
>
> ACK!
>
> Thanks,
> Dscho

Thanks, both.  This indeed is a good update.

>
>>
>>  t/t3427-rebase-subtree.sh | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/t/t3427-rebase-subtree.sh b/t/t3427-rebase-subtree.sh
>> index 39e348de16..bec48e6a1f 100755
>> --- a/t/t3427-rebase-subtree.sh
>> +++ b/t/t3427-rebase-subtree.sh
>> @@ -59,7 +59,10 @@ test_expect_success 'setup' '
>>  	test_commit files_subtree/master5 &&
>>
>>  	git checkout -b to-rebase &&
>> -	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
>> +	git fast-export --no-data HEAD -- files_subtree/ |
>> +		sed -e "s%\([0-9a-f]\{40\} \)files_subtree/%\1%" |
>> +		git fast-import --force --quiet &&
>> +	git reset --hard &&
>>  	git commit -m "Empty commit" --allow-empty
>>  '
>>
>> --
>> 2.22.0.19.ga495766805
>>
>>

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