diff: pass contexts to status

Allow status() to take contexts as well as nodes. This lets us avoid
unpacking manifests multiple times and intelligently unpack manifests
in revision order. Also, we can avoid unpacking manifests at all when
there are no changes in the working directory.

mercurial/localrepo.py

@@ -965,13 +965,24 b' class localrepository(repo.repository):'
                     del mf[fn]
             return mf
 
-        ctx1 = self[node1]
-        ctx2 = self[node2]
+        if isinstance(node1, context.changectx):
+            ctx1 = node1
+        else:
+            ctx1 = self[node1]
+        if isinstance(node2, context.changectx):
+            ctx2 = node2
+        else:
+            ctx2 = self[node2]
+
         working = ctx2 == self[None]
         parentworking = working and ctx1 == self['.']
         match = match or match_.always(self.root, self.getcwd())
         listignored, listclean, listunknown = ignored, clean, unknown
 
+        # load earliest manifest first for caching reasons
+        if not working and ctx2.rev() < ctx1.rev():
+            ctx2.manifest()
+
         if not parentworking:
             def bad(f, msg):
                 if f not in ctx1:

mercurial/patch.py

@@ -1174,21 +1174,18 b' def diff(repo, node1=None, node2=None, m'
             flcache[f] = flctx._filelog
         return flctx
 
-    # reading the data for node1 early allows it to play nicely
-    # with repo.status and the revlog cache.
     ctx1 = repo[node1]
-    # force manifest reading
-    man1 = ctx1.manifest()
-    date1 = util.datestr(ctx1.date())
+    ctx2 = repo[node2]
 
     if not changes:
-        changes = repo.status(node1, node2, match=match)
+        changes = repo.status(ctx1, ctx2, match=match)
     modified, added, removed = changes[:3]
 
     if not modified and not added and not removed:
         return
 
-    ctx2 = repo[node2]
+    date1 = util.datestr(ctx1.date())
+    man1 = ctx1.manifest()
 
     if repo.ui.quiet:
         r = None