Re: Question about merge & cherry pick

[Johannes Sixt <j6t@kdbg.org>]

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