add a regression test for #5450

library/LuaTools.test.cpp

@@ -0,0 +1,74 @@
+// Regression test for https://github.com/DFHack/dfhack/issues/5450
+// (fixed by https://github.com/DFHack/dfhack/pull/5451)
+//
+// df::identity_traits<T>::get() returns a pointer to a *const* instance of
+// a type_identity subclass for most types. When the df_object constraint
+// required a pointer to non-const type_identity, Lua::Push rejected those
+// types and fell back to the bool overload, so e.g. a pointer to a vector
+// arrived in Lua as a boolean.
+
+#include "LuaTools.h"
+#include "LuaWrapper.h"
+
+#include <gtest/gtest.h>
+#include <lualib.h>
+
+#include <cstdint>
+#include <vector>
+
+// The constraint must accept types whose identity is exposed through a
+// pointer-to-const. This is the compile-time half of the regression check:
+// it fails to build if df_object ever becomes too strict again.
+static_assert(DFHack::Lua::df_object<std::vector<int32_t>>);
+static_assert(DFHack::Lua::df_object<int32_t>);
+static_assert(DFHack::Lua::df_object<df::coord>);
+
+class LuaPushTest : public testing::Test {
+protected:
+    lua_State *L = nullptr;
+
+    void SetUp() override
+    {
+        L = luaL_newstate();
+        ASSERT_NE(nullptr, L);
+        luaL_openlibs(L);
+        DFHack::LuaWrapper::AttachDFGlobals(L);
+    }
+
+    void TearDown() override
+    {
+        if (L)
+            lua_close(L);
+    }
+};
+
+TEST_F(LuaPushTest, PushVectorPointer)
+{
+    std::vector<int32_t> vec{ 7, 42 };
+
+    // NB: intentionally avoids df_object-constrained calls below so that
+    // this test still compiles if the constraint regresses - in that case
+    // Push() falls back to the bool overload and the checks fail at runtime
+    DFHack::Lua::Push(L, &vec);
+
+    // the pointer must arrive as a wrapped DF object, not a boolean
+    ASSERT_EQ(LUA_TUSERDATA, lua_type(L, -1));
+    ASSERT_EQ(DFHack::Lua::OBJ_REF, DFHack::Lua::IsDFObject(L, -1));
+
+    // the same pointer must round-trip back out of Lua
+    EXPECT_EQ(static_cast<void*>(&vec),
+        DFHack::Lua::GetDFObject(L, df::identity_traits<std::vector<int32_t>>::get(), -1));
+
+    // and the pushed object must behave like the vector it wraps
+    lua_len(L, -1);
+    EXPECT_EQ(lua_Integer(vec.size()), lua_tointeger(L, -1));
+    lua_pop(L, 1);
+
+    lua_geti(L, -1, 0);
+    EXPECT_EQ(7, lua_tointeger(L, -1));
+    lua_pop(L, 1);
+
+    lua_geti(L, -1, 1);
+    EXPECT_EQ(42, lua_tointeger(L, -1));
+    lua_pop(L, 1);
+}

library/include/LuaWrapper.h

@@ -236,7 +236,7 @@ namespace LuaWrapper {
 
     void IndexStatics(lua_State *state, int meta_idx, int ftable_idx, struct_identity *pstruct);
 
-    void AttachDFGlobals(lua_State *state);
+    DFHACK_EXPORT void AttachDFGlobals(lua_State *state);
 
     DFHACK_EXPORT void notify_deprecated(lua_State* state, std::string_view name, std::string_view message);
 }}