inference error from new Tuple / Vararg types

[vtjnash]

julia> f() = _apply(call, tuple, (f(x)::Vararg,), (f(y)::Vararg,))
f (generic function with 1 method)

julia> code_typed(f,())
ERROR: Vararg type in non-final position
 in abstract_call at ./inference.jl:871
 in abstract_apply at ./inference.jl:766
 in abstract_call at ./inference.jl:814
 in abstract_eval_call at ./inference.jl:901
 in abstract_eval at ./inference.jl:928
 in typeinf_uncached at ./inference.jl:1588
 in typeinf at ./inference.jl:1304
 in code_typed at inference.jl:3256

---

this is a reduced test case from a situation that comes up at the end of building the sysimg with --compile=all when trying to precompile the following definition:

function promote(x, y, zs...)
    # promotion.jl:139
    (convert(promote_typeof(x,y,zs...), x), 
     convert(promote_typeof(x,y,zs...), y), 
     convert(Tuple{Vararg{promote_typeof(x,y,zs...)}}, zs)...)
end

I suspect that issue may come from inferring that the return values of convert(Tuple{Vararg}, zs)...) is Vararg (rather than Any), although the stacktrace shows that this results from attempting to infer the result type of the following expression:

Base.cnvt_all(::Type{_<:Vararg{T<:Any}}, ::Any, ::Vararg{Any}) =

Expr(:call1, top(:_apply), :call, :tuple,
  Expr(:call1, top(:tuple),
    Expr(:call1, :convert, :T, :x)::Vararg{T<:Any}
  )::Tuple{Vararg{T<:Any}},
  Expr(:call1, top(:_apply), :call, :cnvt_all,
    Expr(:call1, top(:tuple), :T)::Tuple{Type{_<:Vararg{T<:Any}}},
    :rest
  )::Tuple{Vararg{T<:Any}}
)::Tuple{Vararg{T<:Any}}

this in turn came from:

Base.convert{T}(::Type{Tuple{_<:Vararg{T}}}, ::Tuple}) =
Expr(:call1, top(:_apply), :call, :cnvt_all, Expr(:call1, top(:tuple), :T)::Tuple{Type{_<:Vararg{T<:Any}}}, :x)::Any

with T=_<:Vararg

note, these are defined in base as:

convert{T}(::Type{Tuple{Vararg{T}}}, x::Tuple) = cnvt_all(T, x...)
cnvt_all(T, x, rest...) = tuple(convert(T,x), cnvt_all(T, rest...)...)

finally, that in turn came from part of our original expression:

Expr(:call, :convert, Expr(:call1, top(:apply_type), :Tuple, Expr(:call1, top(:apply_type), :Vararg, Expr(:call1, top(:_apply), :call, :promote_typeof, Expr(:call1, top(:tuple), :x, :y)::Tuple{Any, Any}, :zs)::Type)::Type{_<:Vararg{T<:Any}})::Type{_<:Tuple{_<:Vararg{T<:Any}}}, :zs)::Any

---

edit: I realized this can also be triggered directly:

julia> code_typed(promote,(Any,Any,Vararg{Any}))
ERROR: Vararg type in non-final position
 in abstract_call at ./inference.jl:871
 in abstract_apply at ./inference.jl:766
 in abstract_call at ./inference.jl:814
 in abstract_eval_call at ./inference.jl:901
 in abstract_eval at ./inference.jl:928
 in typeinf_uncached at ./inference.jl:1588
 in typeinf at ./inference.jl:1304
 in typeinf at ./inference.jl:1254
 in abstract_call_gf at ./inference.jl:693
 in abstract_call at ./inference.jl:837
 in abstract_apply at ./inference.jl:766
 in abstract_call at ./inference.jl:814
 in abstract_eval_call at ./inference.jl:901
 in abstract_eval at ./inference.jl:928
 in typeinf_uncached at ./inference.jl:1588
 in typeinf at ./inference.jl:1304
 in typeinf at ./inference.jl:1254
 in abstract_call_gf at ./inference.jl:693
 in abstract_call at ./inference.jl:837
 in abstract_eval_call at ./inference.jl:901
 in abstract_eval at ./inference.jl:928
 in abstract_eval_call at ./inference.jl:878
 in abstract_eval at ./inference.jl:928
 in typeinf_uncached at ./inference.jl:1588
 in typeinf at ./inference.jl:1304
 in code_typed at inference.jl:3256

[mauro3]

I also stumbled across this. Here's another test-cases in case that helps:

find_tvar{T<:Tuple}(sig::Type{T}) = 1
function find_tvar(arg)
    if arg<:Tuple
        find_tvar(arg[random_var_name])
    end
    return 1
end
find_tvar(Vararg{Int}) # errors with above error

Note that this does not errror:

#find_tvar{T<:Tuple}(sig::Type{T}) = 1
function find_tvar(arg)
    if arg<:Tuple
        find_tvar(arg[random_var_name])
    end
    return 1
end
find_tvar(Vararg{Int})

and this neither

find_tvar{T<:Tuple}(sig::Type{T}) = 1
function find_tvar(arg)
    if arg<:Tuple
        find_tvar(arg[1])
    end
    return 1
end
find_tvar(Vararg{Int})