Add core.compare_block_status function (#11247)

Makes it possible to check the status of the mapblock in a future-extensible way.

Author: SmallJoker

doc/lua_api.txt

@@ -5863,6 +5863,19 @@ Misc.
     * If `transient` is `false` or absent, frees a persistent forceload.
       If `true`, frees a transient forceload.
 
+* `minetest.compare_block_status(pos, condition)`
+    * Checks whether the mapblock at positition `pos` is in the wanted condition.
+    * `condition` may be one of the following values:
+        * `"unknown"`: not in memory
+        * `"emerging"`: in the queue for loading from disk or generating
+        * `"loaded"`: in memory but inactive (no ABMs are executed)
+        * `"active"`: in memory and active
+        * Other values are reserved for future functionality extensions
+    * Return value, the comparison status:
+        * `false`: Mapblock does not fulfil the wanted condition
+        * `true`: Mapblock meets the requirement
+        * `nil`: Unsupported `condition` value
+
 * `minetest.request_insecure_environment()`: returns an environment containing
   insecure functions if the calling mod has been listed as trusted in the
   `secure.trusted_mods` setting or security is disabled, otherwise returns

src/emerge.cpp

@@ -358,6 +358,13 @@ bool EmergeManager::enqueueBlockEmergeEx(
 }
 
 
+bool EmergeManager::isBlockInQueue(v3s16 pos)
+{
+	MutexAutoLock queuelock(m_queue_mutex);
+	return m_blocks_enqueued.find(pos) != m_blocks_enqueued.end();
+}
+
+
 //
 // Mapgen-related helper functions
 //

src/emerge.h

@@ -174,6 +174,8 @@ class EmergeManager {
 		EmergeCompletionCallback callback,
 		void *callback_param);
 
+	bool isBlockInQueue(v3s16 pos);
+
 	v3s16 getContainingChunk(v3s16 blockpos);
 
 	Mapgen *getCurrentMapgen();

src/map.cpp

@@ -1549,6 +1549,11 @@ MapBlock *ServerMap::getBlockOrEmerge(v3s16 p3d)
 	return block;
 }
 
+bool ServerMap::isBlockInQueue(v3s16 pos)
+{
+	return m_emerge && m_emerge->isBlockInQueue(pos);
+}
+
 // N.B.  This requires no synchronization, since data will not be modified unless
 // the VoxelManipulator being updated belongs to the same thread.
 void ServerMap::updateVManip(v3s16 pos)

src/map.h

@@ -365,6 +365,8 @@ class ServerMap : public Map
 	*/
 	MapBlock *getBlockOrEmerge(v3s16 p3d);
 
+	bool isBlockInQueue(v3s16 pos);
+
 	/*
 		Database functions
 	*/

src/mapblock.h

@@ -140,7 +140,7 @@ class MapBlock
 	//// Flags
 	////
 
-	inline bool isDummy()
+	inline bool isDummy() const
 	{
 		return !data;
 	}

src/script/lua_api/l_env.cpp

@@ -46,13 +46,22 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "client/client.h"
 #endif
 
-struct EnumString ModApiEnvMod::es_ClearObjectsMode[] =
+const EnumString ModApiEnvMod::es_ClearObjectsMode[] =
 {
 	{CLEAR_OBJECTS_MODE_FULL,  "full"},
 	{CLEAR_OBJECTS_MODE_QUICK, "quick"},
 	{0, NULL},
 };
 
+const EnumString ModApiEnvMod::es_BlockStatusType[] =
+{
+	{ServerEnvironment::BS_UNKNOWN, "unknown"},
+	{ServerEnvironment::BS_EMERGING, "emerging"},
+	{ServerEnvironment::BS_LOADED,  "loaded"},
+	{ServerEnvironment::BS_ACTIVE,  "active"},
+	{0, NULL},
+};
+
 ///////////////////////////////////////////////////////////////////////////////
 
 
@@ -1389,6 +1398,24 @@ int ModApiEnvMod::l_forceload_block(lua_State *L)
 	return 0;
 }
 
+// compare_block_status(nodepos)
+int ModApiEnvMod::l_compare_block_status(lua_State *L)
+{
+	GET_ENV_PTR;
+
+	v3s16 nodepos = check_v3s16(L, 1);
+	std::string condition_s = luaL_checkstring(L, 2);
+	auto status = env->getBlockStatus(getNodeBlockPos(nodepos));
+	
+	int condition_i = -1;
+	if (!string_to_enum(es_BlockStatusType, condition_i, condition_s))
+		return 0; // Unsupported
+
+	lua_pushboolean(L, status >= condition_i);
+	return 1;
+}
+
+
 // forceload_free_block(blockpos)
 // blockpos = {x=num, y=num, z=num}
 int ModApiEnvMod::l_forceload_free_block(lua_State *L)
@@ -1462,6 +1489,7 @@ void ModApiEnvMod::Initialize(lua_State *L, int top)
 	API_FCT(transforming_liquid_add);
 	API_FCT(forceload_block);
 	API_FCT(forceload_free_block);
+	API_FCT(compare_block_status);
 	API_FCT(get_translated_string);
 }
 

src/script/lua_api/l_env.h

@@ -195,6 +195,9 @@ class ModApiEnvMod : public ModApiBase {
 	// stops forceloading a position
 	static int l_forceload_free_block(lua_State *L);
 
+	// compare_block_status(nodepos)
+	static int l_compare_block_status(lua_State *L);
+
 	// Get a string translated server side
 	static int l_get_translated_string(lua_State * L);
 
@@ -207,7 +210,8 @@ class ModApiEnvMod : public ModApiBase {
 	static void Initialize(lua_State *L, int top);
 	static void InitializeClient(lua_State *L, int top);
 
-	static struct EnumString es_ClearObjectsMode[];
+	static const EnumString es_ClearObjectsMode[];
+	static const EnumString es_BlockStatusType[];
 };
 
 class LuaABM : public ActiveBlockModifier {

src/serverenvironment.cpp

@@ -1542,6 +1542,21 @@ void ServerEnvironment::step(float dtime)
 	m_server->sendDetachedInventories(PEER_ID_INEXISTENT, true);
 }
 
+ServerEnvironment::BlockStatus ServerEnvironment::getBlockStatus(v3s16 blockpos)
+{
+	if (m_active_blocks.contains(blockpos))
+		return BS_ACTIVE;
+
+	const MapBlock *block = m_map->getBlockNoCreateNoEx(blockpos);
+	if (block && !block->isDummy())
+		return BS_LOADED;
+
+	if (m_map->isBlockInQueue(blockpos))
+		return BS_EMERGING;
+
+	return BS_UNKNOWN;
+}
+
 u32 ServerEnvironment::addParticleSpawner(float exptime)
 {
 	// Timers with lifetime 0 do not expire

src/serverenvironment.h

@@ -342,7 +342,16 @@ class ServerEnvironment : public Environment
 	void reportMaxLagEstimate(float f) { m_max_lag_estimate = f; }
 	float getMaxLagEstimate() { return m_max_lag_estimate; }
 
-	std::set<v3s16>* getForceloadedBlocks() { return &m_active_blocks.m_forceloaded_list; };
+	std::set<v3s16>* getForceloadedBlocks() { return &m_active_blocks.m_forceloaded_list; }
+
+	// Sorted by how ready a mapblock is
+	enum BlockStatus {
+		BS_UNKNOWN,
+		BS_EMERGING,
+		BS_LOADED,
+		BS_ACTIVE // always highest value
+	};
+	BlockStatus getBlockStatus(v3s16 blockpos);
 
 	// Sets the static object status all the active objects in the specified block
 	// This is only really needed for deleting blocks from the map