Julia: Inference failure when splatting a number

[dpsanders]

Minimal reproducible example:

julia> immutable MyFunc{F}
               func::F
          end

julia> (f::MyFunc{F}){F}(x) = f.func(x...)

julia> f = MyFunc(x -> 1 + x)
MyFunc{##15#16}(#15)

julia> f((1,))
2

julia> g(f, x) = f(x...)
g (generic function with 1 method)


julia> @code_warntype g(f, (1,))
Variables:
  #self#::#g
  f::MyFunc{##15#16}
  x::Tuple{Int64}

Body:
  begin
      return (Core._apply)((Core.getfield)(f::MyFunc{##15#16},:func)::##15#16,(Core.getfield)(x::Tuple{Int64},1)::Int64)::Any
  end::Any

cc @jrevels

[yuyichao]

It's due to splatting of a number and not a tuple.

julia> f(x) = (x...)
f (generic function with 1 method)

julia> @code_warntype f(1)
Variables:
  #self#::#f
  x::Int64

Body:
  begin 
      return (Core._apply)(Core.tuple,x::Int64)::Tuple
  end::Tuple

julia> f(1)
(1,)

[yuyichao]

And this seems to be caused by the special handling of Core._apply not being able to handle scalar input (or generic iterables). Handling of generic iterables with compile time known size might be useful although it seems non-trivial....

[vtjnash]

would be fixed by https://github.com/JuliaLang/julia/pull/12579 then?

[yuyichao]

Sort of. Although it doesn't infer the length?

[JeffBezanson]

As long as numbers are iterable (which, most likely, they will continue to be) it's worth adding handling for this to _apply inference.

[dpsanders]

This has now been fixed:

julia> @code_warntype g(f, (1,))
Variables:
  #self#::#g
  f::#f
  x::Tuple{Int64}

Body:
  begin
      return (Core.tuple)((Core.getfield)(x::Tuple{Int64}, 1)::Int64, 1)::Tuple{Int64,Int64}
  end::Tuple{Int64,Int64}

[tkelman]

could use a test

[dpsanders]

Good point.

[tkelman]

a partial related test was added in #20343, but it looks a bit different?

[mbauman]

Does this really just need a test in order to close it?

[StefanKarpinski]