Off by one error with api_update_top in lua_rawiter #2053
Description
Luau's api_update_top macro asserts that the new top is less than ci->top, but the comparison should be less-or-equal instead. This macro is currently only used by lua_rawiter.
This results in an error when lua_rawiter is called with a stack size one greater than is needed, e.g. lua_rawiter calls api_update_top(L, top + 2) but this will fail if the stack can increase by exactly only 2.
Example repro:
// Assuming stack size hasn't grown and is still default 20
// Add a table with one item in it (so rawiter does something):
lua_settop(L, 18);
lua_createtable(L, 1, 0);
lua_pushnumber(L, 0);
lua_rawseti(L, -2, 1);
printf("top: %d\n", lua_gettop(L)); // "top: 19"
luaL_checkstack(L, 2, "resize failed"); // We should have a capacity of 21 now
// Throws an error from `api_update_top`:
lua_rawiter(L, -1, 0);Fixing this should be as easy as changing < to <= in the api_check assertion.
Currently:
#define api_update_top(L, p) \
{ \
api_check(L, p >= L->base && p < L->ci->top); \
L->top = p; \
}Proposed api_check fix:
// ...
api_check(L, p >= L->base && p <= L->ci->top); \