hgext/rebase.py

23731:ccbaa2ed11a4

        base = None
    elif not repo[rev].p2():
        # Case (2) detaching the node with a single parent, use this parent
        base = repo[rev].p1().rev()
    else:
        # In case of merge, we need to pick the right parent as merge base.
        #
        # Imagine we have:
        # - M: currently rebase revision in this step
        # - A: one parent of M
        # - B: second parent of M
        # - D: destination of this merge step (p1 var)
        #
        # If we are rebasing on D, D is the successors of A or B. The right
        # merge base is the one D succeed to. We pretend it is B for the rest
        # of this comment
        #
        # If we pick B as the base, the merge involves:
        # - changes from B to M (actual changeset payload)
        # - changes from B to D (induced by rebase) as D is a rebased
        #   version of B)
        # Which exactly represent the rebase operation.
        #
        # If we pick the A as the base, the merge involves
        # - changes from A to M (actual changeset payload)
        # - changes from A to D (with include changes between unrelated A and B
        #   plus changes induced by rebase)
        # Which does not represent anything sensible and creates a lot of
        # conflicts.
        for p in repo[rev].parents():
            if state.get(p.rev()) == p1:
                base = p.rev()
                break
        else: # fallback when base not found

23732:c51d6c043bb1

        base = None
    elif not repo[rev].p2():
        # Case (2) detaching the node with a single parent, use this parent
        base = repo[rev].p1().rev()
    else:
        # Assuming there is a p1, this is the case where there also is a p2.
        # We are thus rebasing a merge and need to pick the right merge base.
        #
        # Imagine we have:
        # - M: current rebase revision in this step
        # - A: one parent of M
        # - B: other parent of M
        # - D: destination of this merge step (p1 var)
        #
        # Consider the case where D is a descendant of A or B and the other is
        # 'outside'. In this case, the right merge base is the D ancestor.
        #
        # An informal proof, assuming A is 'outside' and B is the D ancestor:
        #
        # If we pick B as the base, the merge involves:
        # - changes from B to M (actual changeset payload)
        # - changes from B to D (induced by rebase) as D is a rebased
        #   version of B)
        # Which exactly represent the rebase operation.
        #
        # If we pick A as the base, the merge involves:
        # - changes from A to M (actual changeset payload)
        # - changes from A to D (with include changes between unrelated A and B
        #   plus changes induced by rebase)
        # Which does not represent anything sensible and creates a lot of
        # conflicts. A is thus not the right choice - B is.
        #
        # Note: The base found in this 'proof' is only correct in the specified
        # case. This base does not make sense if is not D a descendant of A or B
        # or if the other is not parent 'outside' (especially not if the other
        # parent has been rebased). The current implementation does not
        # make it feasible to consider different cases separately. In these
        # other cases we currently just leave it to the user to correctly
        # resolve an impossible merge using a wrong ancestor.
        for p in repo[rev].parents():
            if state.get(p.rev()) == p1:
                base = p.rev()
                break
        else: # fallback when base not found