Johan Herland <johan@xxxxxxxxxxx> writes:
> This raises the same question I recently asked Antoine: For a given
> prepackaged merge <X,Y>, do we assume that it only resolves conflicts
> between the changes introduced in commit X vs. changes introduced in
> commit Y, or do we assume that it resolves conflicts between the
> histories leading up to X and Y, respectively? In other words, does
> <X,Y> _supercede_ earlier pre-merges between the histories leading up
> to X and Y?
That is an interesting question. There are largely two cases.
When you replayed M---F to produce N---F', there may have been no
textual or semantic conflict. Which means that there were no new
reason between A--X and B--Y that necessitates an evil merge. A
later merge between a descendant of X (but not Y) and a descendant
of Y (but not X) can cherry pick the same <A,B> (M---F) on top of a
mechanical merge,
On the other hand, you may have had either a textual or a semantic
conflict when replaying <A,B> on N, and you had to fix up F' for it
to be the correct resolution of merge between X and Y.
---o---o---A---o---X
\ \
\ N---F'
\ /
o---B---o---Y
In such a case, you do want to record the fixed N---F' as the
prepackaged resolution for <X,Y>. Any time later when somebody is
on a branch that has X (but not Y) and merges a branch that has Y
(but not X), that N---F' should be the one to cherry-pick on top of
a mechanical merge O between S and T. What <A,B> (M---F) did is
superseded if you are going to replay <X,Y>.
---o---o---A---o---X----------S
\ \ \ \
\ M--F N---F' O---F''
\ / / /
o---B---o---Y----------T
You can tell that by noticing that A is an ancestor of X and B is an
ancestor of Y. As you said, this is a good way to reduce the number
of prepackaged evil merges that need to be considered.
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