Is this `Test.detect_unbound_args` result valid or a bug?

A module:

module M
  f(::Tuple{}) = nothing
  f(::NTuple{n, F}) where {n, F} = F

The second method gets flagged as having an unbound argument, even though the first method protects it from ever being called in such a situation:

julia> detect_unbound_args(M)
[1] f(::Tuple{Vararg{F, n}}) where {n, F} in Main.M at REPL[2]:3

Should this be considered a bug? If not, detect_unbound_args seems useless, as this seems like a very basic false positive. Hope I’m not misunderstanding Julia 101 or something.

This happens with both Julia nightly and with 1.8.5.

It’s definitely annoying. I don’t even know how to call the second method with an empty tuple using invoke.

If you want to avoid it, instead write

f(::Tuple{F,Vararg{F,nMinus1}}) where {F,nMinus1} = ...

I do this. detect_unbound_args is useful, but less so now that you get warnings during precompilation.


Wow, I’ll definitely keep this “tuple type with minimal size” trick in mind.