convert: keep branch switching merges with ancestors (issue3340) When running convert with a filemap, merge parents which are ancestors of other parents are ignored. This is hardly a problem when parents belong to the same branch, but the result could be confusing when named branches are involved. With: -o-a1-a2-a3... <- A \ \ b1-b2-b3...-m- <- B If all b* revisions are discarded, it is useful to preserve 'm' even if it is empty after filtering to record the branch switch. This patch makes filemap preserve "ancestor parents" if there is no "non-ancestor parent" on the same branch than the merge revision. Remarks: - I am not completely convinced by the reasons given above and those detailed by Matt in this thread: http://selenic.com/pipermail/mercurial-devel/2012-May/040627.html The properties we try to preserve are not clearly defined. That said, I know this patch already helped someone on IRC and the tests output look reasonable. - This is a new version of the original "convert: filemap must preserve fast-forward merges" patch. It has exactly the same output for 2 parents merges, the additional complexity is here to handle more than two parents.