Scripting: Allow basic pointer following

include/mgba/script/types.h

@@ -304,6 +304,8 @@ void mScriptValueWrap(struct mScriptValue* val, struct mScriptValue* out);
 struct mScriptValue* mScriptValueUnwrap(struct mScriptValue* val);
 const struct mScriptValue* mScriptValueUnwrapConst(const struct mScriptValue* val);
 
+void mScriptValueFollowPointer(struct mScriptValue* ptr, struct mScriptValue* out);
+
 struct mScriptValue* mScriptStringCreateEmpty(size_t size);
 struct mScriptValue* mScriptStringCreateFromBytes(const void* string, size_t size);
 struct mScriptValue* mScriptStringCreateFromUTF8(const char* string);

src/script/engines/lua.c

@@ -693,6 +693,31 @@ bool _luaWrap(struct mScriptEngineContextLua* luaContext, struct mScriptValue* v
 			return true;
 		}
 	}
+	struct mScriptValue derefPtr;
+	if (value->type->base == mSCRIPT_TYPE_OPAQUE) {
+		if (!value->type->details.type) {
+			return false;
+		}
+		mScriptValueFollowPointer(value, &derefPtr);
+		switch (derefPtr.type->base) {
+		case mSCRIPT_TYPE_VOID:
+		case mSCRIPT_TYPE_SINT:
+		case mSCRIPT_TYPE_UINT:
+		case mSCRIPT_TYPE_FLOAT:
+			value = &derefPtr;
+			break;
+		case mSCRIPT_TYPE_OBJECT:
+			value = mScriptValueAlloc(derefPtr.type);
+			value->value.opaque = derefPtr.value.opaque;
+			weakref = mScriptContextSetWeakref(luaContext->d.context, value);
+			needsWeakref = true;
+			mScriptContextDisownWeakref(luaContext->d.context, weakref);
+			mScriptValueDeref(value);
+			break;
+		default:
+			return false;
+		}
+	}
 	if (value->type == mSCRIPT_TYPE_MS_WEAKREF) {
 		weakref = value->value.u32;
 		value = mScriptContextAccessWeakref(luaContext->d.context, value);

src/script/test/lua.c

@@ -22,6 +22,7 @@ struct Test {
 	void (*vfn0)(struct Test*);
 	void (*vfn1)(struct Test*, int);
 	int32_t (*icfn0)(const struct Test*);
+	struct Test* next;
 };
 
 static int identityInt(int in) {
@@ -83,6 +84,7 @@ mSCRIPT_DECLARE_STRUCT_VOID_METHOD(Test, v1, testV1, 1, S32, b);
 
 mSCRIPT_DEFINE_STRUCT(Test)
 	mSCRIPT_DEFINE_STRUCT_MEMBER(Test, S32, i)
+	mSCRIPT_DEFINE_STRUCT_MEMBER(Test, PS(Test), next)
 	mSCRIPT_DEFINE_STRUCT_METHOD(Test, ifn0)
 	mSCRIPT_DEFINE_STRUCT_METHOD(Test, ifn1)
 	mSCRIPT_DEFINE_STRUCT_METHOD(Test, icfn0)
@@ -726,6 +728,42 @@ M_TEST_DEFINE(callList) {
 	mScriptContextDeinit(&context);
 }
 
+M_TEST_DEFINE(linkedList) {
+	SETUP_LUA;
+
+	struct Test first = {
+		.i = 1
+	};
+	struct Test second = {
+		.i = 2
+	};
+	struct mScriptValue a = mSCRIPT_MAKE_S(Test, &first);
+
+	assert_true(lua->setGlobal(lua, "l", &a));
+	TEST_PROGRAM("assert(l)");
+	TEST_PROGRAM("assert(l.i == 1)");
+	TEST_PROGRAM("assert(not l.next)");
+
+	first.next = &second;
+	TEST_PROGRAM("assert(l)");
+	TEST_PROGRAM("assert(l.i == 1)");
+	TEST_PROGRAM("assert(l.next)");
+	TEST_PROGRAM("assert(l.next.i == 2)");
+	TEST_PROGRAM("assert(not l.next.next)");
+
+	TEST_PROGRAM(
+		"n = l.next\n"
+		"function readN()\n"
+		"	assert(n)\n"
+		"	assert(n.i or not n.i)\n"
+		"end\n"
+		"assert(pcall(readN))\n");
+	// The weakref stored in `n` gets pruned between executions to avoid stale pointers
+	TEST_PROGRAM("assert(not pcall(readN))");
+
+	mScriptContextDeinit(&context);
+}
+
 M_TEST_SUITE_DEFINE_SETUP_TEARDOWN(mScriptLua,
 	cmocka_unit_test(create),
 	cmocka_unit_test(loadGood),
@@ -744,4 +782,5 @@ M_TEST_SUITE_DEFINE_SETUP_TEARDOWN(mScriptLua,
 	cmocka_unit_test(tableLookup),
 	cmocka_unit_test(tableIterate),
 	cmocka_unit_test(callList),
+	cmocka_unit_test(linkedList)
 )

src/script/types.c

@@ -853,6 +853,21 @@ const struct mScriptValue* mScriptValueUnwrapConst(const struct mScriptValue* va
 	return NULL;
 }
 
+void mScriptValueFollowPointer(struct mScriptValue* ptr, struct mScriptValue* out) {
+	if (ptr->type->base != mSCRIPT_TYPE_OPAQUE || !ptr->type->details.type) {
+		return;
+	}
+
+	out->value.opaque = *(void**) ptr->value.opaque;
+	if (out->value.opaque) {
+		out->type = ptr->type->details.type;
+	} else {
+		out->type = mSCRIPT_TYPE_MS_VOID;
+	}
+	out->refs = mSCRIPT_VALUE_UNREF;
+	out->flags = 0;
+}
+
 struct mScriptValue* mScriptStringCreateEmpty(size_t size) {
 	struct mScriptValue* val = mScriptValueAlloc(mSCRIPT_TYPE_MS_STR);
 	struct mScriptString* internal = val->value.opaque;