Re: [PATCH 1/5] git-cherry-pick.txt: do not use 'ORIG_HEAD' in example

[Philippe Blain <levraiphilippeblain@gmail.com>]

Hi Junio,

Le 2023-01-07 à 21:05, Junio C Hamano a écrit :
> "Philippe Blain via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> The command used in the example to abort the cherry-pick is 'git reset
>> --merge ORIG_HEAD', but cherry-pick does not write 'ORIG_HEAD' before
>> starting its operation.
> 
> Sorry, but I am confused.  Doesn't <1> update ORIG_HEAD used by <3>?
> 
>>  $ git cherry-pick topic^             <1>
>>  $ git diff                           <2>
>> -$ git reset --merge ORIG_HEAD        <3>
>> +$ git cherry-pick --abort            <3>
>>  $ git cherry-pick -Xpatience topic^  <4>
>>  ------------
>>  <1> apply the change that would be shown by `git show topic^`.
> 

No, as far as I was able to test and from my reading of the code,
cherry-pick does not write ORIG_HEAD.

Here is a little script that demonstrates this:

```
#!/bin/sh

rm -rf test
git -c init.defaultBranch=master init test
(

cd test
echo hello>file
git add file
git commit -m initial
git branch other
echo two>>file
git commit -am two
git checkout other
echo three >>file
git commit -am three
git checkout master
# This writes ORIG_HEAD as 'two'
git reset HEAD^
git commit -a -m two-redone
# This does not
git cherry-pick other
# This shows ORIG_HEAD written by reset:
echo ORIG_HEAD is:
git log --oneline -1 ORIG_HEAD
# Whereas HEAD is 'two-redone':
echo HEAD is:
git log --oneline -1 HEAD
)
```

Looking at the code, 'git grep -p ORIG_HEAD \*.c'
reveals the only builtin that write ORIG_HEAD are 
am, merge, rebase and reset, and the only library code
that involves ORIG_HEAD is reset.c::reset_head.

Moreover, 'git grep -p [^a-z_]reset_head \*.c'
reveals that the only non-builtin user of reset.c::reset_head
is sequencer.c::create_autostash, in which the RESET_ORIG_HEAD 
flag of 'struct reset_head_opts ropts' is not set.

That is what convinced me that cherry-pick does not write ORIG_HEAD.

Thanks,

Philippe.