# 
# 
# patch "automate.cc"
#  from [2d83f22200a3999fe8416b301f0bbbca0d90723c]
#    to [22bdca832e8d3725dca929762efbc9c9cce0267d]
# 
# patch "cmd_ws_commit.cc"
#  from [5c4576edd5b77a135b612ca40f93c963f778a755]
#    to [72c210276c196dd83a6ffc907d41b1ea3563d2c3]
# 
# patch "database.cc"
#  from [3e65a0b3f6e71edd464d6dc18e8ac46652a44cb1]
#    to [efb940d44464df55a352614fc5ac4db38d5c5945]
# 
# patch "database.hh"
#  from [5d5f3613e3c091f1dc75eb734b86fa4559b03969]
#    to [caaab3649c6ca7d9d6e0be33dd062427a3b5c477]
# 
============================================================
--- automate.cc	2d83f22200a3999fe8416b301f0bbbca0d90723c
+++ automate.cc	22bdca832e8d3725dca929762efbc9c9cce0267d
@@ -1205,49 +1205,18 @@ AUTOMATE(common_ancestors, N_("REV1 [REV
   N(args.size() > 0,
     F("wrong argument count"));
 
-  set<revision_id> ancestors, common_ancestors;
-  vector<revision_id> frontier;
+  set<revision_id> revs, common_ancestors;
   for (vector<utf8>::const_iterator i = args.begin(); i != args.end(); ++i)
     {
       revision_id rid((*i)());
       N(app.db.revision_exists(rid), F("No such revision %s") % rid);
-      ancestors.clear();
-      ancestors.insert(rid);
-      frontier.push_back(rid);
-      while (!frontier.empty())
-        {
-          revision_id rid = frontier.back();
-          frontier.pop_back();
-          if(!null_id(rid))
-            {
-              set<revision_id> parents;
-              app.db.get_revision_parents(rid, parents);
-              for (set<revision_id>::const_iterator i = parents.begin();
-                   i != parents.end(); ++i)
-                {
-                  if (ancestors.find(*i) == ancestors.end())
-                    {
-                      frontier.push_back(*i);
-                      ancestors.insert(*i);
-                    }
-                }
-            }
-        }
-      if (common_ancestors.empty())
-        common_ancestors = ancestors;
-      else
-        {
-          set<revision_id> common;
-          set_intersection(ancestors.begin(), ancestors.end(),
-                         common_ancestors.begin(), common_ancestors.end(),
-                         inserter(common, common.begin()));
-          common_ancestors = common;
-        }
+      revs.insert(rid);
     }
 
+  app.db.get_common_ancestors(revs, common_ancestors);
+
   for (set<revision_id>::const_iterator i = common_ancestors.begin();
        i != common_ancestors.end(); ++i)
-    if (!null_id(*i))
       output << (*i).inner()() << "\n";
 }
 
============================================================
--- cmd_ws_commit.cc	5c4576edd5b77a135b612ca40f93c963f778a755
+++ cmd_ws_commit.cc	72c210276c196dd83a6ffc907d41b1ea3563d2c3
@@ -687,14 +687,63 @@ CMD(branch, N_("workspace"), N_("BRANCHN
   
   branch_name branch(idx(args, 0)());
   
-  // check if the branch cert is already known and refuse if this is right
-  // TODO!!
+  app.require_workspace();
   
+  E(branch != app.opts.branchname,
+    F("branch of the current workspace is already set to %s") % branch);
+
+  std::set<branch_name> branches;
+  app.get_project().get_branch_list(branches);
+  
+  bool existing_branch = false;
+  for (set<branch_name>::const_iterator i = branches.begin();
+    i != branches.end(); ++i)
+    {
+        if (branch == *i)
+          {
+              existing_branch = true;
+              break;
+          }
+    }
+
+  // if this is an existing branch, check if this branch's head revs and
+  // the current workspace parent share any common ancestors, if not warn
+  // the user about it
+  if (existing_branch)
+    {
+        set<revision_id> revs, common_ancestors;
+        app.get_project().get_branch_heads(branch, revs);
+        
+        // FIXME: is there an easier way to just get the revids of the parent(s)
+        // of the current workspace?
+        revision_t work_rev;
+        app.work.get_work_rev(work_rev);
+        for (edge_map::iterator i = work_rev.edges.begin();
+            i != work_rev.edges.end(); i++)
+          {
+              revs.insert(i->first);
+          }
+        
+        app.db.get_common_ancestors(revs, common_ancestors);
+        
+        if (common_ancestors.size() == 0)
+          {
+            W(F("the new branch has no common ancestors with the current branch;\n"
+                "any next commit could therefor create two unmergable heads in\n"
+                "%s") % branch);
+          }
+    }
+  
   // leave the other parameters empty so they won't get changed
   system_path path;
   rsa_keypair_id key;
   
   app.work.set_ws_options(path, branch, key, path);
+  
+  if (existing_branch)
+    P(F("next commit will use the existing branch %s") % branch);
+  else
+    P(F("next commit will use the new branch %s") % branch);
 }
 
 CMD(commit, N_("workspace"), N_("[PATH]..."),
============================================================
--- database.cc	3e65a0b3f6e71edd464d6dc18e8ac46652a44cb1
+++ database.cc	efb940d44464df55a352614fc5ac4db38d5c5945
@@ -1824,6 +1824,59 @@ void
 }
 
 void
+database::get_common_ancestors(std::set<revision_id> const & revs,
+                               std::set<revision_id> & common_ancestors)
+{
+  set<revision_id> ancestors, all_common_ancestors;
+  vector<revision_id> frontier;
+  for (set<revision_id>::const_iterator i = revs.begin(); 
+       i != revs.end(); ++i)
+    {
+      I(revision_exists(*i));
+      ancestors.clear();
+      ancestors.insert(*i);
+      frontier.push_back(*i);
+      while (!frontier.empty())
+        {
+          revision_id rid = frontier.back();
+          frontier.pop_back();
+          if(!null_id(rid))
+            {
+              set<revision_id> parents;
+              get_revision_parents(rid, parents);
+              for (set<revision_id>::const_iterator i = parents.begin();
+                   i != parents.end(); ++i)
+                {
+                  if (ancestors.find(*i) == ancestors.end())
+                    {
+                      frontier.push_back(*i);
+                      ancestors.insert(*i);
+                    }
+                }
+            }
+        }
+      if (all_common_ancestors.empty())
+        all_common_ancestors = ancestors;
+      else
+        {
+          set<revision_id> common;
+          set_intersection(ancestors.begin(), ancestors.end(),
+                         all_common_ancestors.begin(), all_common_ancestors.end(),
+                         inserter(common, common.begin()));
+          all_common_ancestors = common;
+        }
+    }
+    
+  for (set<revision_id>::const_iterator i = all_common_ancestors.begin();
+       i != all_common_ancestors.end(); ++i)
+    {
+      // FIXME: where do these null'ed IDs come from?
+      if (null_id(*i)) continue;
+      common_ancestors.insert(*i);
+    }
+}
+
+void
 database::get_revision(revision_id const & id,
                        revision_t & rev)
 {
============================================================
--- database.hh	5d5f3613e3c091f1dc75eb734b86fa4559b03969
+++ database.hh	caaab3649c6ca7d9d6e0be33dd062427a3b5c477
@@ -296,6 +296,10 @@ public:
 
   void get_revision_manifest(revision_id const & cid,
                              manifest_id & mid);
+
+  void get_common_ancestors(std::set<revision_id> const & revs,
+                            std::set<revision_id> & common_ancestors);
+
 private:
   // helper
   void get_ids(std::string const & table, std::set< hexenc<id> > & ids);