Merge branch 'lua_element_crash' into 'master'

Fix crash when throwing in index meta methods

Closes #7711

See merge request OpenMW/openmw!3862

apps/openmw_test_suite/lua/test_lua.cpp

@@ -51,6 +51,9 @@ return {
 }
 )X");
 
+    TestingOpenMW::VFSTestFile metaIndexErrorFile(
+        "return setmetatable({}, { __index = function(t, key) error('meta index error') end })");
+
     std::string genBigScript()
     {
         std::stringstream buf;
@@ -70,7 +73,7 @@ return {
     {
         std::unique_ptr<VFS::Manager> mVFS = TestingOpenMW::createTestVFS({ { "aaa/counter.lua", &counterFile },
             { "bbb/tests.lua", &testsFile }, { "invalid.lua", &invalidScriptFile }, { "big.lua", &bigScriptFile },
-            { "requireBig.lua", &requireBigScriptFile } });
+            { "requireBig.lua", &requireBigScriptFile }, { "metaIndexError.lua", &metaIndexErrorFile } });
 
         LuaUtil::ScriptsConfiguration mCfg;
         LuaUtil::LuaState mLua{ mVFS.get(), &mCfg };
@@ -223,4 +226,11 @@ return {
         // At this moment all instances of the script should be garbage-collected.
         EXPECT_LT(memWithoutScript, memWithScript);
     }
+
+    TEST_F(LuaStateTest, SafeIndexMetamethod)
+    {
+        sol::table t = mLua.runInNewSandbox("metaIndexError.lua");
+        // without safe get we crash here
+        EXPECT_ERROR(LuaUtil::safeGet(t, "any key"), "meta index error");
+    }
 }

components/lua/luastate.cpp

@@ -376,7 +376,7 @@ namespace LuaUtil
 
     sol::protected_function_result LuaState::throwIfError(sol::protected_function_result&& res)
     {
-        if (!res.valid() && static_cast<int>(res.get_type()) == LUA_TSTRING)
+        if (!res.valid())
             throw std::runtime_error(std::string("Lua error: ") += res.get<sol::error>().what());
         else
             return std::move(res);
@@ -397,7 +397,7 @@ namespace LuaUtil
         std::string fileContent(std::istreambuf_iterator<char>(*mVFS->get(path)), {});
         sol::load_result res = mSol.load(fileContent, path, sol::load_mode::text);
         if (!res.valid())
-            throw std::runtime_error("Lua error: " + res.get<std::string>());
+            throw std::runtime_error(std::string("Lua error: ") += res.get<sol::error>().what());
         return res;
     }
 

components/lua/luastate.hpp

@@ -232,16 +232,36 @@ namespace LuaUtil
         }
     }
 
+    // work around for a (likely) sol3 bug
+    // when the index meta method throws, simply calling table.get crashes instead of re-throwing the error
+    template <class Key>
+    sol::object safeGet(const sol::table& table, const Key& key)
+    {
+        auto index = table.traverse_raw_get<sol::optional<sol::main_protected_function>>(
+            sol::metatable_key, sol::meta_function::index);
+        if (index)
+        {
+            sol::protected_function_result result = index.value()(table, key);
+            if (result.valid())
+                return result.get<sol::object>();
+            else
+                throw result.get<sol::error>();
+        }
+        else
+            return table.raw_get<sol::object>(key);
+    }
+
     // getFieldOrNil(table, "a", "b", "c") returns table["a"]["b"]["c"] or nil if some of the fields doesn't exist.
     template <class... Str>
     sol::object getFieldOrNil(const sol::object& table, std::string_view first, const Str&... str)
     {
         if (!table.is<sol::table>())
             return sol::nil;
+        sol::object value = safeGet(table.as<sol::table>(), first);
         if constexpr (sizeof...(str) == 0)
-            return table.as<sol::table>()[first];
+            return value;
         else
-            return getFieldOrNil(table.as<sol::table>()[first], str...);
+            return getFieldOrNil(value, str...);
     }
 
     // String representation of a Lua object. Should be used for debugging/logging purposes only.