absorb: aborting if another operation is in progress This increases safety of using absorb by both aborting when another operation is in progress (since the absorption could confuse any other command a lot) and holding the locks throughout the reading of the working directory (for which changes to absorb) and the reading of the repo (for which changes to absorb into). Differential Revision: https://phab.mercurial-scm.org/D6237

repoview: keep the branchmap cache for the `served.hidden` view warm For the same reason we want to keep the cache for the `served` view up to date, we want to also keep the `served.hidden` view up to date. If some processes with a readonly access to the repo needs to access it, we better have the cache warm to avoid computing the same data over and over and over. In most case (no secret changesets), the "served" and "served.hidden" set will be identical and no cache will actually have to be updated.

repoview: introduce a filter for serving hidden changesets There are multiple usecase for being able to explicitly view or pull obsolete from a server. We need to be able to do so without exposing the secret changesets. We introduces a dedicated repository "view" to do so. Way to expose this "view" to the user will come later. To keep a behavior consistent with expected client/server behavior, the general idea is for the obsolete access to be explicitly requested by the code generating the request. In addition, the will be server side configuration to restrict the access to this feature.