Add a World::GetPersistentData version that auto-adds if not found.

library/include/DataFuncs.h

@@ -32,6 +32,10 @@ distribution.
 #include "DataIdentity.h"
 #include "LuaWrapper.h"
 
+#ifndef BUILD_DFHACK_LIB
+#error Due to export issues this header is internal to the main library.
+#endif
+
 namespace df {
     // A very simple and stupid implementation of some stuff from boost
     template<class U, class V> struct is_same_type { static const bool value = false; };

library/include/DataIdentity.h

@@ -160,6 +160,8 @@ namespace DFHack
     };
 }
 
+// Due to export issues, this stuff can only work in the main dll
+#ifdef BUILD_DFHACK_LIB
 namespace df
 {
     using DFHack::function_identity_base;
@@ -575,4 +577,4 @@ namespace df
         return &identity;
     }
 }
-
+#endif

library/include/modules/World.h

@@ -139,8 +139,16 @@ namespace DFHack
         PersistentDataItem AddPersistentData(const std::string &key);
         PersistentDataItem GetPersistentData(const std::string &key);
         PersistentDataItem GetPersistentData(int entry_id);
+        // Calls GetPersistentData(key); if not found, adds and sets added to true.
+        // The result can still be not isValid() e.g. if the world is not loaded.
+        PersistentDataItem GetPersistentData(const std::string &key, bool *added);
+        // Lists all items with the given key.
+        // If prefix is true, search for keys starting with key+"/".
+        // GetPersistentData(&vec,"",true) returns all items.
+        // Items have alphabetic order by key; same key ordering is undefined.
         void GetPersistentData(std::vector<PersistentDataItem> *vec,
                                const std::string &key, bool prefix = false);
+        // Deletes the item; returns true if success.
         bool DeletePersistentData(const PersistentDataItem &item);
 
         void ClearPersistentCache();

library/modules/World.cpp

@@ -300,6 +300,21 @@ PersistentDataItem World::GetPersistentData(int entry_id)
     return PersistentDataItem();
 }
 
+PersistentDataItem World::GetPersistentData(const std::string &key, bool *added)
+{
+    *added = false;
+
+    PersistentDataItem rv = GetPersistentData(key);
+
+    if (!rv.isValid())
+    {
+        *added = true;
+        rv = AddPersistentData(key);
+    }
+
+    return rv;
+}
+
 void World::GetPersistentData(std::vector<PersistentDataItem> *vec, const std::string &key, bool prefix)
 {
     if (!BuildPersistentCache())