[PATCH 3 of 5 V2] manifest: introduce manifestlog and manifestctx classes

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1471465513 25200
#      Wed Aug 17 13:25:13 2016 -0700
# Node ID 00f8d3832aad368660c69eff4be3e03a5568aebe
# Parent  8ddbe86953023c40beb7be9dcb8025d1055813c5
manifest: introduce manifestlog and manifestctx classes

This is the start of a large refactoring of the manifest class. It introduces
the new manifestlog and manifestctx classes which will represent the collection
of all manifests and individual instances, respectively.

Future patches will begin to convert usages of repo.manifest to
repo.manifestlog, adding the necessary functionality to manifestlog and instance
as they are needed.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -504,6 +504,10 @@ class localrepository(object):
     def manifest(self):
         return manifest.manifest(self.svfs)
 
+    @storecache('00manifest.i')
+    def manifestlog(self):
+        return manifest.manifestlog(self.svfs, self.manifest)
+
     @repofilecache('dirstate')
     def dirstate(self):
         return dirstate.dirstate(self.vfs, self.ui, self.root,
diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -914,6 +914,70 @@ class manifestrevlog(revlog.revlog):
         super(manifestrevlog, self).clearcaches()
         self._fulltextcache.clear()
 
+class manifestlog(object):
+    """A collection class representing the collection of manifest snapshots
+    referenced by commits in the repository.
+
+    In this situation, 'manifest' refers to the abstract concept of a snapshot
+    of the list of files in the given commit. Consumers of the output of this
+    class do not care about the implementation details of the actual manifests
+    they receive (i.e. tree or flat or lazily loaded, etc)."""
+    def __init__(self, opener, oldmanifest):
+        self._revlog = oldmanifest
+
+        # We'll separate this into it's own cache once oldmanifest is no longer
+        # used
+        self._mancache = oldmanifest._mancache
+
+        # _revlog is the same as _oldmanifest right now, but we eventually want
+        # to delete _oldmanifest while still allowing manifestlog to access the
+        # revlog specific apis.
+        self._oldmanifest = oldmanifest
+
+    def __getitem__(self, node):
+        """Retrieves the manifest instance for the given node. Throws a KeyError
+        if not found.
+        """
+        if (self._oldmanifest._treeondisk
+            or self._oldmanifest._treeinmem):
+            # TODO: come back and support tree manifests directly
+            return self._oldmanifest.read(node)
+
+        if node == revlog.nullid:
+            return manifestdict()
+        if node in self._mancache:
+            cachemf = self._mancache[node]
+            # The old manifest may put non-ctx manifests in the cache, so skip
+            # those since they don't implement the full api.
+            if isinstance(cachemf, manifestctx):
+                return cachemf
+
+        m = manifestctx(self._revlog, node)
+        self._mancache[node] = m
+        return m
+
+class manifestctx(manifestdict):
+    """A class representing a single revision of a manifest, including its
+    contents, its parent revs, and its linkrev.
+    """
+    def __init__(self, revlog, node):
+        self._revlog = revlog
+
+        self._node = node
+        self.p1, self.p2 = revlog.parents(node)
+        rev = revlog.rev(node)
+        self.linkrev = revlog.linkrev(rev)
+
+        # This should eventually be made lazy loaded, so consumers can access
+        # the node/p1/linkrev data without having to parse the whole manifest.
+        data = revlog.revision(node)
+        arraytext = array.array('c', data)
+        revlog._fulltextcache[node] = arraytext
+        super(manifestctx, self).__init__(data)
+
+    def node(self):
+        return self._node
+
 class manifest(manifestrevlog):
     def __init__(self, opener, dir='', dirlogcache=None):
         '''The 'dir' and 'dirlogcache' arguments are for internal use by