rebase: allow collapsing branches in place (issue3111) We allow rebase plus collapse, but not collapse only? I imagine people would rebase first then collapse once they are sure the rebase is correct and it is the right time to finish it. I was reluctant to submit this patch for reasons detailed below, but it improves rebase --collapse usefulness so much it is worth the ugliness. The fix is ugly because we should be fixing the collapse code path rather than the merge. Collapsing by merging changesets repeatedly is inefficient compared to what commit --amend does: commitctx(), update, strip. The problem with the latter is, to generate the synthetic changeset, copy records are gathered with copies.pathcopies(). copies.pathcopies() is still implemented with merging in mind and discards information like file replaced by the copy of another, criss-cross copies and so forth. I believe this information should not be lost, even if we decide not to interpret it fully later, at merge time. The second issue with improving rebase --collapse is the option should not be there to begin with. Rebasing and collapsing are orthogonal and a dedicated command would probably enable a better, simpler ui. We should avoid advertizing rebase --collapse, but with this fix it becomes the best shipped solution to collapse changesets. And for the record, available techniques are: - revert + commit + strip: lose copies - mq/qfold: repeated patching() (mostly correct, fragile) - rebase: repeated merges (mostly correct, fragile) - collapse: revert + tag rewriting wizardry, lose copies - histedit: repeated patching() (mostly correct, fragile) - amend: copies.pathcopies() + commitctx() + update + strip