Saveload: Fix SlNullPointers with upstream chunks

src/saveload/saveload.cpp

@@ -184,7 +184,7 @@ void SlNullPointers()
 	/* We don't want any savegame conversion code to run
 	 * during NULLing; especially those that try to get
 	 * pointers from other pools. */
-	_sl_version = SAVEGAME_VERSION;
+	_sl_version = MAX_LOAD_SAVEGAME_VERSION;
 
 	for (const ChunkHandler &ch : ChunkHandlers()) {
 		DEBUG(sl, 3, "Nulling pointers for %c%c%c%c", ch.id >> 24, ch.id >> 16, ch.id >> 8, ch.id);
@@ -2038,12 +2038,24 @@ void SlFixPointers()
 
 void SlFixPointerChunkByID(uint32_t id)
 {
+	_sl.action = SLA_PTRS;
+
 	const ChunkHandler *ch = SlFindChunkHandler(id);
 	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
 	DEBUG(sl, 3, "Fixing pointers for %c%c%c%c", ch->id >> 24, ch->id >> 16, ch->id >> 8, ch->id);
 	ch->FixPointers();
 }
 
+void SlNullPointerChunkByID(uint32_t id)
+{
+	_sl.action = SLA_NULL;
+
+	const ChunkHandler *ch = SlFindChunkHandler(id);
+	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
+	DEBUG(sl, 3, "Nulling pointers for %c%c%c%c", ch->id >> 24, ch->id >> 16, ch->id >> 8, ch->id);
+	ch->FixPointers();
+}
+
 /**
  * Save a chunk of data (eg. vehicles, stations, etc.). Each chunk is
  * prefixed by an ID identifying it, followed by data, and terminator where appropriate

src/sl/saveload.cpp

@@ -91,6 +91,7 @@ extern bool _sl_upstream_mode;
 
 namespace upstream_sl {
 	void SlNullPointers();
+	void SlNullPointerChunkByID(uint32_t);
 	void SlLoadChunks();
 	void SlLoadChunkByID(uint32_t id);
 	void SlLoadCheckChunks();
@@ -380,6 +381,14 @@ static void SlNullPointers()
 
 	_sl.action = SLA_NULL;
 
+	/* Do upstream chunk tests before clearing version data */
+	ring_buffer<uint32_t> upstream_null_chunks;
+	for (auto &ch : ChunkHandlers()) {
+		if (ch.special_proc != nullptr && ch.special_proc(ch.id, CSLSO_PRE_NULL_PTRS) == CSLSOR_UPSTREAM_NULL_PTRS) {
+			upstream_null_chunks.push_back(ch.id);
+		}
+	}
+
 	/* We don't want any savegame conversion code to run
 	 * during NULLing; especially those that try to get
 	 * pointers from other pools. */
@@ -387,9 +396,14 @@ static void SlNullPointers()
 	SlXvSetCurrentState();
 
 	for (auto &ch : ChunkHandlers()) {
-		if (ch.special_proc != nullptr) {
+		if (!upstream_null_chunks.empty() && upstream_null_chunks.front() == ch.id) {
-			if (ch.special_proc(ch.id, CSLSO_PRE_PTRS) == CSLSOR_LOAD_CHUNK_CONSUMED) continue;
+			upstream_null_chunks.pop_front();
+			SlExecWithSlVersion(MAX_LOAD_SAVEGAME_VERSION, [&]() {
+				upstream_sl::SlNullPointerChunkByID(ch.id);
+			});
+			continue;
 		}
+
 		if (ch.ptrs_proc != nullptr) {
 			DEBUG(sl, 3, "Nulling pointers for %c%c%c%c", ch.id >> 24, ch.id >> 16, ch.id >> 8, ch.id);
 			ch.ptrs_proc();

src/sl/saveload.h

@@ -90,6 +90,7 @@ enum ChunkSaveLoadSpecialOp {
 	CSLSO_PRE_LOAD,
 	CSLSO_PRE_LOADCHECK,
 	CSLSO_PRE_PTRS,
+	CSLSO_PRE_NULL_PTRS,
 	CSLSO_SHOULD_SAVE_CHUNK,
 };
 enum ChunkSaveLoadSpecialOpResult {
@@ -97,6 +98,7 @@ enum ChunkSaveLoadSpecialOpResult {
 	CSLSOR_LOAD_CHUNK_CONSUMED,
 	CSLSOR_DONT_SAVE_CHUNK,
 	CSLSOR_UPSTREAM_SAVE_CHUNK,
+	CSLSOR_UPSTREAM_NULL_PTRS,
 };
 typedef ChunkSaveLoadSpecialOpResult ChunkSaveLoadSpecialProc(uint32_t, ChunkSaveLoadSpecialOp);
 
@@ -189,6 +191,8 @@ namespace upstream_sl {
 						SlFixPointerChunkByID(id);
 					});
 					return CSLSOR_LOAD_CHUNK_CONSUMED;
+				case CSLSO_PRE_NULL_PTRS:
+					return CSLSOR_UPSTREAM_NULL_PTRS;
 				case CSLSO_SHOULD_SAVE_CHUNK:
 					return CSLSOR_UPSTREAM_SAVE_CHUNK;
 				default:
@@ -234,6 +238,9 @@ namespace upstream_sl {
 						SlFixPointerChunkByID(id);
 					});
 					return CSLSOR_LOAD_CHUNK_CONSUMED;
+				case CSLSO_PRE_NULL_PTRS:
+					if (!F::LoadUpstream()) return CSLSOR_NONE;
+					return CSLSOR_UPSTREAM_NULL_PTRS;
 				case CSLSO_SHOULD_SAVE_CHUNK:
 					return F::SaveUpstream() ? CSLSOR_UPSTREAM_SAVE_CHUNK : CSLSOR_NONE;
 				default: