Index: src/info.c
==================================================================
--- src/info.c
+++ src/info.c
@@ -674,10 +674,12 @@
       @   <td>
       @     %z(href("%R/tree?ci=%S",zUuid))files</a>
       @   | %z(href("%R/fileage?name=%S",zUuid))file ages</a>
       @   | %z(href("%R/tree?nofiles&type=tree&ci=%S",zUuid))folders</a>
       @   | %z(href("%R/artifact/%S",zUuid))manifest</a>
+      @   | %z(href("%R/vdiff?from=pbranch:%S&to=%S",zUuid,zUuid))
+      @           branch diff</a>
       if( g.perm.Write ){
         @   | %z(href("%R/ci_edit?r=%S",zUuid))edit</a>
       }
       @   </td>
       @ </tr>

Index: src/name.c
==================================================================
--- src/name.c
+++ src/name.c
@@ -181,10 +181,19 @@
       " WHERE mtime<=julianday('%qz') AND type GLOB '%q'"
       " ORDER BY mtime DESC LIMIT 1",
       &zTag[4], zType);
     return rid;
   }
+
+  /* "pbranch:", as for parent branch.  It returns the checkin of
+     the last checkin of the parent branch that has been merged in. */
+  if( memcmp(zTag, "pbranch:", 8)==0 ){
+    rid = symbolic_name_to_rid(&zTag[8], zType);
+    if( rid==0 ) return 0; /* TODO: Negative rid allowed here? */
+    rid = get_parent_branch_rid(rid);
+    return rid;
+  }
 
   /* "tag:" + symbolic-name */
   if( memcmp(zTag, "tag:", 4)==0 ){
     rid = db_int(0,
        "SELECT event.objid, max(event.mtime)"
@@ -1058,5 +1067,108 @@
 */
 void test_phatoms_cmd(void){
   db_find_and_open_repository(0,0);
   describe_artifacts_to_stdout("IN (SELECT rid FROM blob WHERE size<0)", 0);
 }
+
+/*
+** Returns the rid for the last checkin where the parent branch was merged.
+*/
+int get_parent_branch_rid(
+  int branchRid /* The rid to find parent branch for. */
+){
+  Stmt s;
+  char *branchName = 0;       /* Name of the branch at rid */
+  char *parentBranchName = 0; /* Name of the parent branch */
+  int rid;
+
+  /* Get the name of the current branch */
+  branchName = db_text(0,
+    "SELECT value FROM tagxref"
+    " WHERE tagid=%d"
+    "   AND tagxref.tagtype>0"
+    "   AND rid=%d",
+    TAG_BRANCH, branchRid
+  );
+
+  if( !branchName )
+    return 0;
+
+  /* Find the name of the branch this was forked from */
+  db_prepare(&s,
+    "SELECT pid, tagxref.value FROM plink JOIN tagxref"
+    " WHERE cid=:rid"
+    "   AND isprim=1"
+    "   AND tagxref.tagid=%d"
+    "   AND tagxref.tagtype>0"
+    "   AND tagxref.rid=pid",
+    TAG_BRANCH
+  );
+  rid = branchRid;
+  while( rid>0 ){
+    db_bind_int(&s, ":rid", rid);
+    if( db_step(&s)==SQLITE_ROW ){
+      const char *zValue; /* Branch name of the pid */
+      rid = db_column_int(&s, 0);
+      zValue = db_column_text(&s, 1);
+      if( !zValue ){
+        rid = 0;
+        break;
+      }
+      if( fossil_strcmp(zValue,branchName) ){
+        parentBranchName = fossil_strdup(zValue);
+        break;
+      }
+    }else{
+      rid = 0;
+      break;
+    }
+    db_reset(&s);
+  }
+  db_finalize(&s);
+
+  if( rid==0 ){
+    fossil_free(branchName);
+    fossil_free(parentBranchName);
+    return 0;
+  }
+
+  /* Find the last checkin coming from the parent branch */
+  db_prepare(&s,
+    "SELECT pid, tagxref.value FROM plink JOIN tagxref"
+    " WHERE cid=:rid"
+    "   AND tagxref.tagid=%d"
+    "   AND tagxref.tagtype>0"
+    "   AND tagxref.rid=pid ORDER BY isprim ASC",
+    TAG_BRANCH
+  );
+  rid = branchRid;
+  while( rid>0 ){
+    db_bind_int(&s, ":rid", rid);
+    int found = 0;
+    while( db_step(&s)==SQLITE_ROW ){
+      const char *zValue; /* Branch name of the pid */
+      found++;
+      rid = db_column_int(&s, 0);
+      zValue = db_column_text(&s, 1);
+      if( !zValue ){
+        break;
+      }
+      if( fossil_strcmp(parentBranchName,zValue)==0 ){
+        /* Found the last merge from the parent branch */
+        db_finalize(&s);
+        fossil_free(branchName);
+        fossil_free(parentBranchName);
+        return rid;
+      }
+    }
+    if( found==0 ){
+      break;
+    }
+    db_reset(&s);
+  }
+  db_finalize(&s);
+
+  fossil_free(branchName);
+  fossil_free(parentBranchName);
+  return 0;
+}