[LUA] Add custom Lua require loader to resolve modules via the engine file system.

src/xrScriptEngine/script_engine.cpp

@@ -781,6 +781,79 @@ struct luajit
     }
 };
 
+// Custom `require` loader resolving modules through the engine file system.
+// Unlike the default package.path loader, it also finds scripts packed inside game archives,
+// with loose gamedata files taking priority over archived ones,
+// consistently with how the engine resolves every other game asset.
+//
+// Example:
+// `local example = require("scripts.folder.file")` imports `gamedata\scripts\folder\file.script`
+static int gamedata_module_loader(lua_State* L)
+{
+    pcstr moduleName = lua_tostring(L, 1);
+
+    string_path fileName;
+    xr_strcpy(fileName, moduleName);
+    for (char* c = fileName; *c; ++c)
+    {
+        if (*c == '.')
+            *c = _DELIMITER;
+    }
+    xr_strcat(fileName, ".script");
+
+    string_path filePath;
+    FS.update_path(filePath, "$game_data$", fileName);
+
+    IReader* reader = FS.r_open(filePath);
+    if (!reader)
+    {
+        // Not an error: report the candidate path and let the remaining searchers try
+        lua_pushfstring(L, "\n\tno file '%s' in engine file system", filePath);
+        return 1;
+    }
+
+    string_path chunkName;
+    strconcat(sizeof(chunkName), chunkName, "@", filePath);
+
+    const int errorCode = luaL_loadbuffer(L, static_cast<LPCSTR>(reader->pointer()), reader->length(), chunkName);
+    FS.r_close(reader);
+
+    if (errorCode)
+    {
+        return lua_error(L);
+    }
+
+    return 1;
+}
+
+// Adds gamedata folder as module root for lua `require` and allows usage of built-in lua module system.
+//
+// Example:
+// `local example = require("scripts.folder.file")` tries to import `gamedata\scripts\folder\file.script`
+static void setup_gamedata_module_loading(lua_State* L)
+{
+    // Engine file system loader, resolves modules packed inside game archives as well.
+    // Registered after package.preload (index 1), before the default package.path loader:
+    // table.insert(package.loaders, 2, gamedata_module_loader)
+    lua_getglobal(L, "table");
+    lua_getfield(L, -1, "insert");
+    lua_remove(L, -2);
+    lua_getglobal(L, "package");
+    lua_getfield(L, -1, "loaders");
+    lua_remove(L, -2);
+    lua_pushinteger(L, 2);
+    lua_pushcfunction(L, gamedata_module_loader);
+    lua_call(L, 3, 0);
+
+    string_path gamedataPath;
+    string_path packagePath;
+
+    FS.update_path(gamedataPath, "$game_data$", "?.script;");
+    xr_sprintf(packagePath, "package.path = package.path .. [[%s]]", gamedataPath);
+
+    luaL_dostring(L, packagePath);
+}
+
 void CScriptEngine::init(export_func exporter, bool loadGlobalNamespace)
 {
     ZoneScoped;
@@ -851,20 +924,7 @@ void CScriptEngine::init(export_func exporter, bool loadGlobalNamespace)
             luaL_dostring(lua(), mathRandom);
     }
 
-    // Adds gamedata folder as module root for lua `require` and allows usage of built-in lua module system.
-    // Notes:
-    // - Does not resolve files inside archived game files
-    // Example:
-    // `local example = require("scripts.folder.file")` tries to import `gamedata\scripts\folder\file.script`
-    {
-        string_path gamedataPath;
-        string_path packagePath;
-
-        FS.update_path(gamedataPath, "$game_data$", "?.script;");
-        xr_sprintf(packagePath, "package.path = package.path .. [[%s]]", gamedataPath);
-
-        luaL_dostring(lua(), packagePath);
-     }
+    setup_gamedata_module_loading(lua());
 
     // XXX nitrocaster: with vanilla scripts, '-nojit' option requires script profiler to be disabled. The reason
     // is that lua hooks somehow make 'super' global unavailable (is's used all over the vanilla scripts).