treemanifest: create treemanifest class There are a number of problems with large and flat manifests. Copying from http://mercurial.selenic.com/wiki/ManifestShardingPlan: * manifest too large for RAM * manifest resolution too much CPU (long delta chains) * committing is slow because entire manifest has to be hashed * impossible for narrow clone to leave out part of manifest as all is needed to calculate new hash * diffing two revisions involves traversing entire subdirectories even if identical This is a first step in a series introducing a manifest revlog per directory. This change adds a new manifest class: treemanifest, which is a tree where each node has a dict of files (nodeids), a dict of flags, and a dict of subdirectories (treemanifests). So far, it behaves just like manifestdict, but it will later help us write one manifest revlog per directory. The new class is still unused; it will be used after the next change. The code is not yet optimized. Running with it (see below) makes most or all operations slower. Once we start storing manifest revlogs for every directory, it should be possible to make many of these operations much faster. The fastdelta() optimization has been intentionally not implemented for the treemanifests. We can implement it later if necessary. All tests pass when run with the following patch (and without, of couse): --- a/mercurial/manifest.py Thu Mar 19 11:08:42 2015 -0700 +++ b/mercurial/manifest.py Thu Mar 19 11:15:50 2015 -0700 @@ -596,7 +596,7 @@ class manifest(revlog.revlog): return None, None def add(self, m, transaction, link, p1, p2, added, removed): - if p1 in self._mancache: + if False and p1 in self._mancache: # If our first parent is in the manifest cache, we can # compute a delta here using properties we know about the # manifest up-front, which may save time later for the @@ -626,3 +626,5 @@ class manifest(revlog.revlog): self._mancache[n] = (m, arraytext) return n + +manifestdict = treemanifest