Interactive squash/reorder and rebase-with-history about git-imerge HOT 1 CLOSED

It's not possible. Suppose the original diagram is

o - A - B    <- master

and you want to exchange the order of commits A and B while preserving history. The resulting diagram would have to look something like this:

o - A - B
     \ /
      X
     / \
    B'- A'   <- master

(The X simply means that the lines cross, and the dependencies go upwards; e.g., B is a parent of B'.) But this is incorrect, because A is an ancestor of B' (via B), which implies that the state B' includes the changes that were originally made in commit A. But in fact, B' does not include those changes; in the rebased commits, the changes originally introduced by A are only introduced in the delta from B' to A'.

So there is no way to preserve history when reordering commits while also preserving the correct commit ancestry.

(It is possible to use incremental-merge tricks to reorder history, and I hope to write that up soon. But it is impossible to record the result of such a commit-reordering in a history-preserving way.)

from git-imerge.