# Question: rerere preimage format

2 messages from 2023-12-16 to 2023-12-16. Participants: Mohamed Mohey, Junio C Hamano.
Thread: https://gitlist.dev/t/60621

## Mohamed Mohey, 2023-12-16 15:46

Subject: Question: rerere preimage format
Message-ID: <CAAY9aimx4X2jDaFz+jWtAj==g+J3QA8LKPQFePyGFhVvbwKNtQ@mail.gmail.com>
URL: https://gitlist.dev/e/CAAY9aimx4X2jDaFz%2BjWtAj%3D%3Dg%2BJ3QA8LKPQFePyGFhVvbwKNtQ%40mail.gmail.com

```
Hi,

I was reading the Rerere section of the Pro Git book when I came
across the following snippet:

$ git rerere diff
--- a/hello.rb
+++ b/hello.rb
@@ -1,11 +1,11 @@
 #! /usr/bin/env ruby
 def hello
-<<<<<<<
-  puts 'hello mundo'
-=======
+<<<<<<< HEAD
   puts 'hola world'
->>>>>>>
+=======
+  puts 'hello mundo'
+>>>>>>> i18n-world
 end

If I understand correctly, this is the diff between rerere's preimage
and the version in the current working directory, as explained in this
StackOverflow answer:

https://stackoverflow.com/a/27364585


What I don't understand, however, is why rerere records its initial
preimage without labels. This seems to have been rerere's behavior
ever since it was introduced as a perl script back in 2006:

https://lore.kernel.org/git/7v4q3no0v7.fsf@assigned-by-dhcp.cox.net/

+ $one = join('', @{$side[0]});
+ $two = join('', @{$side[1]});
+ if ($two le $one) {
+ ($one, $two) = ($two, $one);
+ }
+ print $out "<<<<<<<\n";
+ print $out $one;
+ print $out "=======\n";
+ print $out $two;
+ print $out ">>>>>>>\n";
+ @side = ();


So the preimage format doesn't contain any labels, and outputs the
lexicographically smaller hunk first,
while the default merge conflict output has labels and outputs the
current branch first followed by the other branch.

If rerere recorded its preimage in the same format as the default
merge conflict format,
the above rerere diff output would be empty as there would be no
difference between what we started with and what we resolved into.

The same behaviour would still occur with the diff3 style format, for
example, but at least it wouldn't occur with the default merge style
format.

My question is:

Is there a reason rerere's output is like this that I'm missing? Or is
it just there for convenience since it doesn't affect rerere's
intended functionality?


Thanks,
Mohamed Mohey

```

## Junio C Hamano, 2023-12-16 17:34

Subject: Re: Question: rerere preimage format
Message-ID: <xmqq34w2jbky.fsf@gitster.g>
URL: https://gitlist.dev/e/xmqq34w2jbky.fsf%40gitster.g
In-Reply-To: <CAAY9aimx4X2jDaFz+jWtAj==g+J3QA8LKPQFePyGFhVvbwKNtQ@mail.gmail.com>

```
Mohamed Mohey <mmi9433@gmail.com> writes:

> My question is:
>
> Is there a reason rerere's output is like this that I'm missing? Or is
> it just there for convenience since it doesn't affect rerere's
> intended functionality?
>
>
> Thanks,
> Mohamed Mohey

Documentation/technical/rerere.txt would be a good place to start.


```