Re: How to revert to a specific commit?

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 3, 2024, 00:57 UTC
Message-ID: <xmqqser5h9c6.fsf@gitster.g>
In-Reply-To: <CAPx1Gve_dCRux9_cF7NTspomS4K=Hp_y74d94S-Hm0amuovUqQ@mail.gmail.com>

Chris Torek <chris.torek@gmail.com> writes:

Show 23 quoted lines

> On Mon, Dec 2, 2024 at 4:15 AM tao lv <thebookofunknowable@gmail.com> wrote:
>> I want to revert the code to a specific commit. ...
>
> OK, first some background:
>
>  * A commit _is_ a full snapshot of every file, as of the state
>    it had at the time you (or whoever) made that particular
>    commit. Hence, if you want the particular files from a
>    particular commit, you simply check out that (historical)
>    commit.
>
> Now:
>
>> I don't want to revert each individual commit; I just want to restore
>> the code to this specific commit while retaining all the current
>> history commits.
>>
>> How can I achieve this? Is there a better way than using the revert function?
>
>     git checkout [--detach] <hash>   # or git switch --detach <hash>
>     git reset --soft <branch-name>
>
>     git restore --no-overlay -S -W <hash>

While that would _work_ in the sense that you can revert the effect of what the discarded commits did, I would not recommend any of the above since it does not leave any record of what you discarded.

Imagine that I regret doing everything since we tagged, say, v2.47.0 release and want to discard everythig on 'master' newer than that commit. If I want to "keep" the history of failed commits that I regret having made since v2.47.0, here is a way to do it:

 $ git checkout master
 $ git reset --hard v2.47.0
 $ git merge -s ours --no-ff -m 'Discard everything since v2.47.0' master@{1}

The first two steps just discard the unwanted commits. The third step is a trick to

 - Keep the tree contents of the current commit (i.e. -s ours) as
   the result,

 - Make sure the result is recorded as a merge commit (i.e.
   --no-ff), not "fast-forward" to the tip of the history I am
   discarding, and

 - Record the discarded history (i.e. master@{1}) as the side branch
   of the resulting history.

The last part would help if I later need to merge changes that were based on 'master' I am discarding. The presense of the side branch makes sure that only the effects from the new work done on the discarded history, and not from the commits such a new work was based on (which are the commits I regret having made and I am discarding), are taken into account when computing further merges.