Add "MINETEST_MOD_PATH" environment variable (#11515)

This adds an environment variable MINETEST_MOD_PATH.
When it exists, Minetest will look there for mods in addition to ~/.minetest/mods/.

12 files changed, 74 insertions, 6 deletions

diff --git a/builtin/mainmenu/pkgmgr.lua b/builtin/mainmenu/pkgmgr.lua
index 787936e31..76d4a4123 100644
--- a/builtin/mainmenu/pkgmgr.lua
+++ b/builtin/mainmenu/pkgmgr.lua
@@ -682,11 +682,9 @@ function pkgmgr.preparemodlist(data)
 	local game_mods = {}
 
 	--read global mods
-	local modpath = core.get_modpath()
-
-	if modpath ~= nil and
-		modpath ~= "" then
-		get_mods(modpath,global_mods)
+	local modpaths = core.get_modpaths()
+	for _, modpath in ipairs(modpaths) do
+		get_mods(modpath, global_mods)
 	end
 
 	for i=1,#global_mods,1 do
diff --git a/doc/menu_lua_api.txt b/doc/menu_lua_api.txt
index f4dfff261..b4b6eaba2 100644
--- a/doc/menu_lua_api.txt
+++ b/doc/menu_lua_api.txt
@@ -219,7 +219,13 @@ Package - content which is downloadable from the content db, may or may not be i
     * returns path to global user data,
       the directory that contains user-provided mods, worlds, games, and texture packs.
 * core.get_modpath() (possible in async calls)
-    * returns path to global modpath
+    * returns path to global modpath, where mods can be installed
+* core.get_modpaths() (possible in async calls)
+    * returns list of paths to global modpaths, where mods have been installed
+
+      The difference with "core.get_modpath" is that no mods should be installed in these
+      directories by Minetest -- they might be read-only.
+
 * core.get_clientmodpath() (possible in async calls)
     * returns path to global client-side modpath
 * core.get_gamepath() (possible in async calls)
diff --git a/doc/minetest.6 b/doc/minetest.6
index bac70fe1a..42ed1a45f 100644
--- a/doc/minetest.6
+++ b/doc/minetest.6
@@ -119,6 +119,9 @@ Display an interactive terminal over ncurses during execution.
 .TP
 .B MINETEST_SUBGAME_PATH
 Colon delimited list of directories to search for games.
+.TP
+.B MINETEST_MOD_PATH
+Colon delimited list of directories to search for mods.
 
 .SH BUGS
 Please report all bugs at https://github.com/minetest/minetest/issues.
diff --git a/src/content/subgames.cpp b/src/content/subgames.cpp
index e9dc609b0..30447c838 100644
--- a/src/content/subgames.cpp
+++ b/src/content/subgames.cpp
@@ -113,6 +113,10 @@ SubgameSpec findSubgame(const std::string &id)
 	if (user != share || user_game)
 		mods_paths.insert(user + DIR_DELIM + "mods");
 
+	for (const std::string &mod_path : getEnvModPaths()) {
+		mods_paths.insert(mod_path);
+	}
+
 	// Get meta
 	std::string conf_path = game_path + DIR_DELIM + "game.conf";
 	Settings conf;
@@ -384,3 +388,13 @@ void loadGameConfAndInitWorld(const std::string &path, const std::string &name,
 	if (new_game_settings)
 		delete game_settings;
 }
+
+std::vector<std::string> getEnvModPaths()
+{
+	const char *c_mod_path = getenv("MINETEST_MOD_PATH");
+	std::vector<std::string> paths;
+	Strfnd search_paths(c_mod_path ? c_mod_path : "");
+	while (!search_paths.at_end())
+		paths.push_back(search_paths.next(PATH_DELIM));
+	return paths;
+}
diff --git a/src/content/subgames.h b/src/content/subgames.h
index 60392639b..4a50803e8 100644
--- a/src/content/subgames.h
+++ b/src/content/subgames.h
@@ -58,6 +58,8 @@ SubgameSpec findWorldSubgame(const std::string &world_path);
 
 std::set<std::string> getAvailableGameIds();
 std::vector<SubgameSpec> getAvailableGames();
+// Get the list of paths to mods in the environment variable $MINETEST_MOD_PATH
+std::vector<std::string> getEnvModPaths();
 
 bool getWorldExists(const std::string &world_path);
 //! Try to get the displayed name of a world
diff --git a/src/script/lua_api/l_mainmenu.cpp b/src/script/lua_api/l_mainmenu.cpp
index 6e9a5c34f..57fddc0be 100644
--- a/src/script/lua_api/l_mainmenu.cpp
+++ b/src/script/lua_api/l_mainmenu.cpp
@@ -503,6 +503,21 @@ int ModApiMainMenu::l_get_modpath(lua_State *L)
 }
 
 /******************************************************************************/
+int ModApiMainMenu::l_get_modpaths(lua_State *L)
+{
+	int index = 1;
+	lua_newtable(L);
+	ModApiMainMenu::l_get_modpath(L);
+	lua_rawseti(L, -2, index);
+	for (const std::string &component : getEnvModPaths()) {
+		index++;
+		lua_pushstring(L, component.c_str());
+		lua_rawseti(L, -2, index);
+	}
+	return 1;
+}
+
+/******************************************************************************/
 int ModApiMainMenu::l_get_clientmodpath(lua_State *L)
 {
 	std::string modpath = fs::RemoveRelativePathComponents(
@@ -856,6 +871,7 @@ void ModApiMainMenu::Initialize(lua_State *L, int top)
 	API_FCT(get_mapgen_names);
 	API_FCT(get_user_path);
 	API_FCT(get_modpath);
+	API_FCT(get_modpaths);
 	API_FCT(get_clientmodpath);
 	API_FCT(get_gamepath);
 	API_FCT(get_texturepath);
@@ -889,6 +905,7 @@ void ModApiMainMenu::InitializeAsync(lua_State *L, int top)
 	API_FCT(get_mapgen_names);
 	API_FCT(get_user_path);
 	API_FCT(get_modpath);
+	API_FCT(get_modpaths);
 	API_FCT(get_clientmodpath);
 	API_FCT(get_gamepath);
 	API_FCT(get_texturepath);
diff --git a/src/script/lua_api/l_mainmenu.h b/src/script/lua_api/l_mainmenu.h
index ec2d20da2..781185425 100644
--- a/src/script/lua_api/l_mainmenu.h
+++ b/src/script/lua_api/l_mainmenu.h
@@ -112,6 +112,8 @@ private:
 
 	static int l_get_modpath(lua_State *L);
 
+	static int l_get_modpaths(lua_State *L);
+
 	static int l_get_clientmodpath(lua_State *L);
 
 	static int l_get_gamepath(lua_State *L);
diff --git a/src/unittest/CMakeLists.txt b/src/unittest/CMakeLists.txt
index 5703b8906..52f870901 100644
--- a/src/unittest/CMakeLists.txt
+++ b/src/unittest/CMakeLists.txt
@@ -44,6 +44,7 @@ set (UNITTEST_CLIENT_SRCS
 
 set (TEST_WORLDDIR ${CMAKE_CURRENT_SOURCE_DIR}/test_world)
 set (TEST_SUBGAME_PATH ${CMAKE_CURRENT_SOURCE_DIR}/../../games/devtest)
+set (TEST_MOD_PATH ${CMAKE_CURRENT_SOURCE_DIR}/test_mod)
 
 configure_file(
 	"${CMAKE_CURRENT_SOURCE_DIR}/test_config.h.in"
diff --git a/src/unittest/test_config.h.in b/src/unittest/test_config.h.in
index 36850b00d..50d2398e4 100644
--- a/src/unittest/test_config.h.in
+++ b/src/unittest/test_config.h.in
@@ -4,3 +4,4 @@
 
 #define TEST_WORLDDIR "@TEST_WORLDDIR@"
 #define TEST_SUBGAME_PATH "@TEST_SUBGAME_PATH@"
+#define TEST_MOD_PATH "@TEST_MOD_PATH@"
diff --git a/src/unittest/test_mod/test_mod/init.lua b/src/unittest/test_mod/test_mod/init.lua
new file mode 100644
index 000000000..724a863f5
--- /dev/null
+++ b/src/unittest/test_mod/test_mod/init.lua
@@ -0,0 +1 @@
+-- deliberately empty
diff --git a/src/unittest/test_mod/test_mod/mod.conf b/src/unittest/test_mod/test_mod/mod.conf
new file mode 100644
index 000000000..56c64b2d8
--- /dev/null
+++ b/src/unittest/test_mod/test_mod/mod.conf
@@ -0,0 +1,2 @@
+name = test_mod
+description = A mod doing nothing, to test if MINETEST_MOD_PATH is recognised
diff --git a/src/unittest/test_servermodmanager.cpp b/src/unittest/test_servermodmanager.cpp
index e3edb0c32..4c473d8b5 100644
--- a/src/unittest/test_servermodmanager.cpp
+++ b/src/unittest/test_servermodmanager.cpp
@@ -48,14 +48,20 @@ static TestServerModManager g_test_instance;
 void TestServerModManager::runTests(IGameDef *gamedef)
 {
 	const char *saved_env_mt_subgame_path = getenv("MINETEST_SUBGAME_PATH");
+	const char *saved_env_mt_mod_path = getenv("MINETEST_MOD_PATH");
 #ifdef WIN32
 	{
 		std::string subgame_path("MINETEST_SUBGAME_PATH=");
 		subgame_path.append(TEST_SUBGAME_PATH);
 		_putenv(subgame_path.c_str());
+
+		std::string mod_path("MINETEST_MOD_PATH=");
+		mod_path.append(TEST_MOD_PATH);
+		_putenv(mod_path.c_str());
 	}
 #else
 	setenv("MINETEST_SUBGAME_PATH", TEST_SUBGAME_PATH, 1);
+	setenv("MINETEST_MOD_PATH", TEST_MOD_PATH, 1);
 #endif
 
 	TEST(testCreation);
@@ -75,12 +81,21 @@ void TestServerModManager::runTests(IGameDef *gamedef)
 		if (saved_env_mt_subgame_path)
 			subgame_path.append(saved_env_mt_subgame_path);
 		_putenv(subgame_path.c_str());
+
+		std::string mod_path("MINETEST_MOD_PATH=");
+		if (saved_env_mt_mod_path)
+			mod_path.append(saved_env_mt_mod_path);
+		_putenv(mod_path.c_str());
 	}
 #else
 	if (saved_env_mt_subgame_path)
 		setenv("MINETEST_SUBGAME_PATH", saved_env_mt_subgame_path, 1);
 	else
 		unsetenv("MINETEST_SUBGAME_PATH");
+	if (saved_env_mt_mod_path)
+		setenv("MINETEST_MOD_PATH", saved_env_mt_mod_path, 1);
+	else
+		unsetenv("MINETEST_MOD_PATH");
 #endif
 }
 
@@ -89,6 +104,7 @@ void TestServerModManager::testCreation()
 	std::string path = std::string(TEST_WORLDDIR) + DIR_DELIM + "world.mt";
 	Settings world_config;
 	world_config.set("gameid", "devtest");
+	world_config.set("load_mod_test_mod", "true");
 	UASSERTEQ(bool, world_config.updateConfigFile(path.c_str()), true);
 	ServerModManager sm(TEST_WORLDDIR);
 }
@@ -119,16 +135,21 @@ void TestServerModManager::testGetMods()
 	UASSERTEQ(bool, mods.empty(), false);
 
 	// Ensure we found basenodes mod (part of devtest)
+	// and test_mod (for testing MINETEST_MOD_PATH).
 	bool default_found = false;
+	bool test_mod_found = false;
 	for (const auto &m : mods) {
 		if (m.name == "basenodes")
 			default_found = true;
+		if (m.name == "test_mod")
+			test_mod_found = true;
 
 		// Verify if paths are not empty
 		UASSERTEQ(bool, m.path.empty(), false);
 	}
 
 	UASSERTEQ(bool, default_found, true);
+	UASSERTEQ(bool, test_mod_found, true);
 }
 
 void TestServerModManager::testGetModspec()