> Note that the second argument must be present. It is not marked as optional.
This semantics is incompatible with section 3.4.11, which says:
When a function is called, the list of arguments is adjusted to the length of the list of parameters, unless the function is a vararg function, which is indicated by three dots ('...') at the end of its parameter list.
Several lines further in the text, we have an example:
function f(a, b) end
[...]
CALL PARAMETERS
f(3) a=3, b=nil
This, per the manual, a non-vararg argument, if omitted, is nil. This implies that the call setmetatable(t), which is not vararg, shall be equivalent to setmetabable(t, nil), which has a specified meaning.
I should say that the TNONE vs TNIL difference is very arcane and confusing. And this difference only exists for C functions, and one can make a C function conform with the documented behaviour (3.4.11), or not.
