Errror in accumulate when I have one argument as a tuple

[pevnak]

Errror in accumulate when I have one argument as a tuple

[nmheim]

Zygote is constructing tangents that enter the decumulate pullback via wrap_chainrules_output. in this case its hitting the method for Union{Tuple,NamedTuple} which is interesting, because I think it should be using the method for Tuple.

I think this could be fixed by making sure wrap_chainrules_output returns a StructuralTangent... or at least if in zygote I do:

@inline function wrap_chainrules_input(dxs::Union{Tuple, NamedTuple})
  xp = map(wrap_chainrules_input, dxs)
  # This produces Tangent{Any} since it does not get to see the primal, `x`.
  # ChainRulesCore.Tangent{Any, typeof(xp)}(xp) -- comment this out and replace by line below
  ChainRulesCore.StructuralTangent{typeof(xp)}(xp)
end

things seem to work out

[mcabbott]

Same error with JuliaDiff/ChainRules.jl#569, FWIW.

Not certain this is relevant, but notice the similarity to this:

julia> accumulate(=>, (1,2,3))
(1, 1 => 2, (1 => 2) => 3)

julia> accumulate(=>, [1,2,3])
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Pair{Int64, Int64}

and that this gradient works with x::Tuple:

julia> gradient(α -> sum(sum(g(α, h, Tuple(x)))), 1f0)[1]
15.059713f0

julia> gradient(α -> sum(sum(g(α, h, x))), 1f0)[1]  # with x::Vector as above
ERROR: MethodError: no method matching construct(::Type{Any}, ::Tuple{FillArrays.Fill{Float32, 1, Tuple{Base.OneTo{Int64}}}, ChainRulesCore.NoTangent})