dagop: use heap to compute max rev in filectxancestors()

dagop: add smartset interface to filectxancestors() The original filectx API is kept public since we'll need it to walk ancestor (rev, match) pairs efficiently. The current implementation scans ancestors twice for 'hg log -fp FILE'.

overlayworkingctx: add `_checkexist(path)` This is in preparation to switch this class to inheriting (and being based off a) `commitctx` instead of a `workingctx`. `filectx` has no `exists` function, so this is how we'll fall back in that case. Differential Revision: https://phab.mercurial-scm.org/D1237

overlayworkingctx: fix a bad reference to `self._path` Differential Revision: https://phab.mercurial-scm.org/D1236

overlayworkingctx: track copy information in the context We can no longer do so in the dirstate, so add the functions to do so here. Differential Revision: https://phab.mercurial-scm.org/D1235

rebaseruntime: raise InMemoryMergeConflictsError on merge conflicts Differential Revision: https://phab.mercurial-scm.org/D1234

rebase: do not bail on uncomitted changes if rebasing in-memory Differential Revision: https://phab.mercurial-scm.org/D1233

rebase: add the --inmemory option flag; assign a wctx object for the rebase In the future, the --inmemory flag might be deprecated in favor of something more intelligent (for example, always rebasing in-memory if the working copy parent isn't in the rebaseset). But we might keep it as a way to explicitly force IMM on or off. Differential Revision: https://phab.mercurial-scm.org/D1232

overlayworkingctx: move _wrappedctx out of the constructor With rebase, we will be setting the _wrappedctx at a different point from the wctx construction (somewhat later, and possibly several times). Move it to a public function. Differential Revision: https://phab.mercurial-scm.org/D1231

merge: don't check for unknown files in IMM Differential Revision: https://phab.mercurial-scm.org/D1214

rebase: enable multidest by default This was intended to be done by D470. But there was a minor documentation issue. The feature is quite usable now so it gets formally documented and enabled. There is no behavior change for people not using the `SRC` or `ALLSRC` in rebase destination revset. .. feature:: Rebase with different destination per source revision Previously, rebase only supports one unique destination. Now ``SRC`` and ``ALLSRC`` can be used in rebase destination revset to precisely define destination per each individual source revision. For example, the following command could move some orphaned changesets to reasonable new places so they become no longer orphaned:: hg rebase -r 'orphan()-obsolete()' -d 'max((successors(max(roots(ALLSRC) & ::SRC)^)-obsolete())::)' Differential Revision: https://phab.mercurial-scm.org/D1063

overlayworkingctx: make clean() public It will be called directly by rebase after concluding a node. Differential Revision: https://phab.mercurial-scm.org/D1230

overlayworkingctx: remove flushall() Differential Revision: https://phab.mercurial-scm.org/D1216

merge: skip subrepo state, update hooks, and updating the dirstate in IMM Differential Revision: https://phab.mercurial-scm.org/D1215

merge: remove calls to flushall() Since D1105, these are unnecessary since IMM will now never use workers. Differential Revision: https://phab.mercurial-scm.org/D1213

filemerge: raise InMemoryMergeConflictsError if we hit merge conflicts in IMM Merge conflicts might be supported in the future, but for now are kept out of scope. Any places where we used to call `flushall()` should be replaced with some kind of exception. At this point, IMM M1 is no longer supported. Differential Revision: https://phab.mercurial-scm.org/D1212