manifest: define and implement rev() on manifestlog

Various code is accessing repo.manifestlog._revlog - a private
attribute. This bypasses our interface and makes it difficult to
implement non-revlog manifest storage.

This commit adds a rev() method to the manifestlog interface and
class and teaches callers to use it.

Ideally this method wouldn't exist, as very few consumers should
need to resolve the revision number of a manifest. Again, the
primary goal of interface work is to establish and use interfaces
first and to improve them later.

Differential Revision: https://phab.mercurial-scm.org/D3882

mercurial/logcmdutil.py

@@ -228,7 +228,7 b' class changesetprinter(object):'
 
         if self.ui.debugflag and rev is not None:
             mnode = ctx.manifestnode()
-            mrev = self.repo.manifestlog._revlog.rev(mnode)
+            mrev = self.repo.manifestlog.rev(mnode)
             self.ui.write(columns['manifest']
                           % scmutil.formatrevnode(self.ui, mrev, mnode),
                           label='ui.debug log.manifest')

mercurial/manifest.py

@@ -1348,6 +1348,9 b' class manifestlog(object):'
         self._dirmancache.clear()
         self._revlog.clearcaches()
 
+    def rev(self, node):
+        return self._revlog.rev(node)
+
 @interfaceutil.implementer(repository.imanifestrevisionwritable)
 class memmanifestctx(object):
     def __init__(self, manifestlog):

mercurial/repository.py

@@ -922,6 +922,12 b' class imanifestlog(interfaceutil.Interfa'
     def clearcaches():
         """Clear caches associated with this collection."""
 
+    def rev(node):
+        """Obtain the revision number for a binary node.
+
+        Raises ``error.LookupError`` if the node is not known.
+        """
+
 class completelocalrepository(interfaceutil.Interface):
     """Monolithic interface for local repositories.
 

mercurial/templatekw.py

@@ -465,7 +465,7 b' def showmanifest(context, mapping):'
     if mnode is None:
         # just avoid crash, we might want to use the 'ff...' hash in future
         return
-    mrev = repo.manifestlog._revlog.rev(mnode)
+    mrev = repo.manifestlog.rev(mnode)
     mhex = hex(mnode)
     mapping = context.overlaymap(mapping, {'rev': mrev, 'node': mhex})
     f = context.process('manifest', mapping)