ENH: add REMOVE_DUPLICATES subcommand to LIST command (and test). Remove duplicates from a list (keep the ordering)

Source/cmListCommand.cxx

@@ -59,6 +59,10 @@ bool cmListCommand
     {
     return this->HandleRemoveItemCommand(args);
     }
+  if(subCommand == "REMOVE_DUPLICATES")
+    {
+    return this->HandleRemoveDuplicatesCommand(args);
+    }
   if(subCommand == "SORT")
     {
     return this->HandleSortCommand(args);
@@ -392,6 +396,68 @@ bool cmListCommand
   return true;
 }
 
+//----------------------------------------------------------------------------
+bool cmListCommand
+::HandleRemoveDuplicatesCommand(std::vector<std::string> const& args)
+{
+  if(args.size() < 2)
+    {
+    this->SetError("sub-command REMOVE_DUPLICATES requires a list as an argument.");
+    return false;
+    }
+
+  const std::string& listName = args[1];
+  // expand the variable
+  std::vector<std::string> varArgsExpanded;
+  if ( !this->GetList(varArgsExpanded, listName.c_str()) )
+    {
+    this->SetError("sub-command REMOVE_DUPLICATES requires list to be present.");
+    return false;
+    }
+
+  std::string value;
+
+#if 0 
+  // Fast version, but does not keep the ordering
+
+  std::set<std::string> unique(varArgsExpanded.begin(), varArgsExpanded.end());
+  std::set<std::string>::iterator it;
+  for ( it = unique.begin(); it != unique.end(); ++ it )
+    {
+    if (value.size())
+      {
+      value += ";";
+      }
+    value += it->c_str();
+    }
+
+#else
+
+  // Slower version, keep the ordering
+
+  std::set<std::string> unique;
+  std::vector<std::string>::iterator it;
+  for ( it = varArgsExpanded.begin(); it != varArgsExpanded.end(); ++ it )
+    {
+    if (unique.find(*it) != unique.end())
+      {
+      continue;
+      }
+    unique.insert(*it);
+
+    if (value.size())
+      {
+      value += ";";
+      }
+    value += it->c_str();
+    }
+#endif
+
+
+  this->Makefile->AddDefinition(listName.c_str(), value.c_str());
+  return true;
+}
+
 //----------------------------------------------------------------------------
 bool cmListCommand
 ::HandleSortCommand(std::vector<std::string> const& args)