For example, with this topology:
- o---o---o---B
- /
+ o---o---o---B
+ /
---o---1---o---o---o---A
the merge base between 'A' and 'B' is '1'.
When the history involves criss-cross merges, there can be more than one
'best' common ancestor for two commits. For example, with this topology:
- ---1---o---A
- \ /
- X
- / \
- ---2---o---o---B
+ ---1---o---A
+ \ /
+ X
+ / \
+ ---2---o---o---B
both '1' and '2' are merge-bases of A and B. Neither one is better than
the other (both are 'best' merge bases). When the `--all` option is not given,
`origin/master` may have been rewound and rebuilt, leading to a
history of this shape:
- o---B1
- /
+ o---B1
+ /
---o---o---B2--o---o---o---B (origin/master)
- \
- B3
- \
- Derived (topic)
+ \
+ B3
+ \
+ Derived (topic)
where `origin/master` used to point at commits B3, B2, B1 and now it
points at B, and your `topic` branch was started on top of it back
this:
---o---o---o---M---x---x---W
- /
+ /
---A---B
where A and B are on the side development that was not so good, M is the
may look like this:
---o---o---o---M---x---x---W---x
- /
+ /
---A---B-------------------C---D
where C and D are to fix what was broken in A and B, and you may already
which would make the history look like this:
---o---o---o---M---x---x---W---x---Y
- /
+ /
---A---B-------------------C---D
where Y is the revert of W. Such a "revert of the revert" can be done
changed) be equivalent to not having W or Y at all in the history:
---o---o---o---M---x---x-------x----
- /
+ /
---A---B-------------------C---D
and merging the side branch again will not have conflict arising from an
earlier revert and revert of the revert.
---o---o---o---M---x---x-------x-------*
- / /
+ / /
---A---B-------------------C---D
Of course the changes made in C and D still can conflict with what was
after the revert, the history would have looked like this:
---o---o---o---M---x---x---W---x---x
- / \
+ / \
---A---B A'--B'--C'
If you reverted the revert in such a case as in the previous example:
---o---o---o---M---x---x---W---x---x---Y---*
- / \ /
+ / \ /
---A---B A'--B'--C'
where Y is the revert of W, A' and B' are rerolled A and B, and there may
of revert" blindly without thinking..
---o---o---o---M---x---x---W---x---x
- / \
+ / \
---A---B A'--B'--C'
In the history with rebased side branch, W (and M) are behind the merge