compare: backout 51c4d2e74898 to fix ancestor calculation to empty repository This case can not just be simplified as I thought it could. Mercurial 3.4 has d2de20e1451f 'revset: extend fullreposet to make "null" revision magically appears in set' Which makes ancestor(id(0000000000),1) 'correctly' return the null revision as ancestor. We can however not rely on that when supporting Mercurial 3.3.