# 
# patch "commands.cc"
#  from [e1dec5c24b9716e26504b76091f7954d68985f40]
#    to [af9078ec98297982cd41e7a8b0cea758e9a9df6c]
# 
# patch "merge.cc"
#  from [635075b4158cb7a383660663cd9347d667d658f5]
#    to [b0b447f677a2e152f0d9cf15afeee01ee23c88c4]
# 
# patch "revision.cc"
#  from [e0469a524455b86a3867af582fd4e7149553374c]
#    to [660a3bf2779b462955c45cc154e37639e23eb6a3]
# 
# patch "revision.hh"
#  from [a0449ad6861f9f989c1baab0aae2dfe9d47e9466]
#    to [3bd95a5f0eeee3f31b8e6f835046d757b4b63488]
# 
========================================================================
--- commands.cc	e1dec5c24b9716e26504b76091f7954d68985f40
+++ commands.cc	af9078ec98297982cd41e7a8b0cea758e9a9df6c
@@ -2285,9 +2285,7 @@
   get_working_revision_and_rosters(app, args, rs, old_roster, new_roster, excluded_work);
   calculate_ident(rs, rid);
 
-  N(!(rs.edges.size() == 0 || 
-      edge_changes(rs.edges.begin()).empty()), 
-    F("no changes to commit\n"));
+  N(rs.is_nontrivial(), F("no changes to commit\n"));
     
   cert_value branchname;
   I(rs.edges.size() == 1);
========================================================================
--- merge.cc	635075b4158cb7a383660663cd9347d667d658f5
+++ merge.cc	b0b447f677a2e152f0d9cf15afeee01ee23c88c4
@@ -10,6 +10,7 @@
 #include "merge.hh"
 #include "roster_merge.hh"
 #include "packet.hh"
+#include "safe_map.hh"
 
 void
 interactive_merge_and_store(revision_id const & left_rid,
========================================================================
--- revision.cc	e0469a524455b86a3867af582fd4e7149553374c
+++ revision.cc	660a3bf2779b462955c45cc154e37639e23eb6a3
@@ -40,36 +40,33 @@
 
 void revision_set::check_sane() const
 {
-/*
-// FIXME_ROSTERS: disabled until rewritten to use rosters
   I(!null_id(new_manifest));
-
-  manifest_map fragment;
-  for (edge_map::const_iterator i = edges.begin(); i != edges.end(); ++i)
+  if (edges.size() == 1)
     {
-      change_set const & cs = edge_changes(i);
-      cs.check_sane();
-      if (!global_sanity.relaxed)
+      // null revision is allowed iff there is a null manifest
+      I(null_id(edge_old_revision(edges.begin()))
+        == null_id(edge_old_manifest(edges.begin())));
+    }
+  else if (edges.size() == 2)
+    {
+      // merge nodes cannot have null revisions or null manifests, ever
+      for (edge_map::const_iterator i = edges.begin(); i != edges.end(); ++i)
         {
-          // null old revisions come with null old manifests
-          I(!null_id(edge_old_revision(i)) || null_id(edge_old_manifest(i)));
+          I(!null_id(edge_old_revision(i)));
+          I(!null_id(edge_old_manifest(i)));
+          if (!(new_manifest == edge_old_manifest(i)))
+            I(!edge_changes(i).empty());
         }
-      for (change_set::delta_map::const_iterator j = cs.deltas.begin(); j != cs.deltas.end(); ++j)
-        {
-          manifest_map::const_iterator k = fragment.find(delta_entry_path(j));
-          if (k == fragment.end())
-            fragment.insert(std::make_pair(delta_entry_path(j),
-                                           delta_entry_dst(j)));
-          else
-            {
-              if (!global_sanity.relaxed)
-                {                  
-                  I(delta_entry_dst(j) == manifest_entry_id(k));
-                }
-            }
-        }
     }
-*/
+  else
+    // revisions must always have either 1 or 2 edges
+    I(false);
+
+  // we used to also check that if there were multiple edges that had patches
+  // for the same file, then the new hashes on each edge matched each other.
+  // this is not ported over to roster-style revisions because it's an
+  // inadequate check, and the real check, that the new manifest id is correct
+  // (done in put_revision, for instance) covers this case automatically.
 }
 
 bool 
@@ -78,6 +75,19 @@
   return edges.size() > 1; 
 }
 
+bool
+revision_set::is_nontrivial() const
+{
+  check_sane();
+  // merge revisions are never trivial, because even if the resulting node
+  // happens to be identical to both parents, the merge is still recording
+  // that fact.
+  if (is_merge_node())
+    return true;
+  else
+    return !edge_changes(edges.begin()).empty();
+}
+
 revision_set::revision_set(revision_set const & other)
 {
   /* behave like normal constructor if other is empty */
========================================================================
--- revision.hh	a0449ad6861f9f989c1baab0aae2dfe9d47e9466
+++ revision.hh	3bd95a5f0eeee3f31b8e6f835046d757b4b63488
@@ -56,6 +56,9 @@
 {
   void check_sane() const;
   bool is_merge_node() const;
+  // trivial revisions are ones that have no effect -- e.g., commit should
+  // refuse to commit them, saying that there are no changes to commit.
+  bool is_nontrivial() const;
   revision_set() {}
   revision_set(revision_set const & other);
   revision_set const & operator=(revision_set const & other);
@@ -164,10 +167,10 @@
 // frontier set of shared_ptr<roster_t>s, while traversing history.
 void
 select_nodes_modified_by_rev(revision_id const & rid,
-			     revision_set const & rev,
-			     std::set<node_id> & nodes_changed,
-			     std::set<node_id> & nodes_born,
-			     app_state & app);
+                             revision_set const & rev,
+                             std::set<node_id> & nodes_changed,
+                             std::set<node_id> & nodes_born,
+                             app_state & app);
 
 /*
 void