What does skipping ancestral prediction mean when using graft?

Question

I use the graft command to pull 4 change sets from BranchA to BranchB. When I do this, some are vaccinated and some are not:

 PS D:\Dev\ProjectAlpha> hg graft 5f403abb2b24 skipping ancestor revision 15911 PS D:\Dev\ProjectAlpha> hg graft 535ff712c5a3 grafting revision 15925 PS D:\Dev\ProjectAlpha> hg graft cf42b7113e02 grafting revision 15931 PS D:\Dev\ProjectAlpha> hg graft 6920922ee602 skipping ancestor revision 15910 

I can not find anything documented to explain this. I can find the source, but perhaps it would be useful to someone else if someone could come and explain it.

Is there a transplant procedure I need to keep in mind? Am I doing it wrong?

Answer 1

From hg help glossary :

 Ancestor Any changeset that can be reached by an unbroken chain of parent changesets from a given changeset. More precisely, the ancestors of a changeset can be defined by two properties: a parent of a changeset is an ancestor, and a parent of an ancestor is an ancestor. See also: 'Descendant'. 

therefore, the transplant refuses to make these changes the descendants of your current set of changes, because they are already the ancestors of your current set of changes, and the presence of your ancestors - your descendants, as shown, does not work in the films "Back to the Future" .;)