Even very basic broadcasting breaks inferability

[oxinabox]

Even very simple broadcasting can't infer in Diffractor forward mode

Consider:

using Diffractor
using Diffractor: TaylorBundle, ZeroBundle, CompositeBundle
forward = Diffractor.∂☆{1}()
f(x) = 2 .* x
cb = CompositeBundle{1, Tuple{Float64, Float64}}((TaylorBundle{1}(1.0, (1.0,)), TaylorBundle{1}(1.0, (2.0,))))
@code_warntype forward(ZeroBundle{1}(f), cb)

The output is

julia> @code_warntype forward(ZeroBundle{1}(f), cb)
MethodInstance for (::Diffractor.∂☆{1})(::ZeroBundle{1, typeof(f)}, ::CompositeBundle{1, Tuple{Float64, Float64}, Tuple{Diffractor.TangentBundle{1, Float64, Diffractor.TaylorTangent{Tuple{Float64}}}, Diffractor.TangentBundle{1, Float64, Diffractor.TaylorTangent{Tuple{Float64}}}}})
  from (::Diffractor.∂☆{N})(args::Diffractor.AbstractTangentBundle{N}...) where N @ Diffractor ~/.julia/packages/Diffractor/a9mlv/src/stage1/forward.jl:148
Static Parameters
  N = 1
Arguments
  #self#::Core.Const(Diffractor.∂☆{1}())
  args::Tuple{ZeroBundle{1, typeof(f)}, CompositeBundle{1, Tuple{Float64, Float64}, Tuple{Diffractor.TangentBundle{1, Float64, Diffractor.TaylorTangent{Tuple{Float64}}}, Diffractor.TangentBundle{1, Float64, Diffractor.TaylorTangent{Tuple{Float64}}}}}}
Body::Any
1 ─ %1 = Core.apply_type(Diffractor.∂☆internal, $(Expr(:static_parameter, 1)))::Core.Const(Diffractor.∂☆internal{1})
│   %2 = (%1)()::Core.Const(Diffractor.∂☆internal{1}())
│   %3 = Core._apply_iterate(Base.iterate, %2, args)::Any
└──      return %3