Re: Question about merge & cherry pick

From: Johannes Sixt <j6t@kdbg.org>
Date: Nov 7, 2024, 06:37 UTC
Message-ID: <eb367098-0c88-4bc6-b824-32ee6e6d273e@kdbg.org>
In-Reply-To: <711a0faa-6d82-48b6-819d-9ddbeda03f6a@maurel.me>

Am 06.11.24 um 21:24 schrieb Julien Maurel:

> From my point of view, after these operations, content on branch master
> and dev should be same with "zZz" on second line and "eDe" on last one.
> But it's not the case on second line...

The behavior that you observe is as intended and not a bug.

You have this (consider each letter on its own line):

          A Z Q E       initial commit
         /       \
     A Y Q E      |     dev: Z -> Y
        |         |
        |     A Y Q E   master: cherry-pick Z -> Y
        |         |
     A Z Q D      |     dev: revert Y -> Z and change E -> D
         \        /
          A Y Q D       merge

Your expectation that the merge result is "A Z Q D" is wrong. Consider what happened on the dev branch (left) since the branches diverged: Since the change from Z to Y was reverted to Z, the only change that the dev side contributes to the merge is that of E to D. The master side, on the other hand, contributes the change of Z to Y. So the total of the merge must be Z to Y from the master side and E to D from the dev side, and that is what you get.

A merge does not consider the individual changes on the branches, but only the differences since the merge base. For the merge operation, the change from Z to Y never happened on the dev side. The reversal of Y to Z is not visible for the merge and cannot contribute to the result.

-- Hannes