sum with a function where that function returns a tuple

[oxinabox]

MWE:

julia> using Zygote;

julia> function foo(xs)
       sum(xs) do x
           (2*x, 3*x)
       end
       end
foo (generic function with 1 method)

julia> Zygote.pullback(foo, [1.0, 2.0, 3.0])
ERROR: MethodError: no method matching +(::Tuple{Float64, Float64}, ::Tuple{Float64, Float64})
The function `+` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  +(::Any, ::Any, ::Any, ::Any...)
   @ Base operators.jl:596
  +(::ChainRulesCore.ZeroTangent, ::Any)
   @ ChainRulesCore ~/.julia/packages/ChainRulesCore/U6wNx/src/tangent_arithmetic.jl:99
  +(::Any, ::ChainRulesCore.NotImplemented)
   @ ChainRulesCore ~/.julia/packages/ChainRulesCore/U6wNx/src/tangent_arithmetic.jl:25
  ...

Stacktrace:
  [1] add_sum(x::Tuple{Float64, Float64}, y::Tuple{Float64, Float64})
    @ Base ./reduce.jl:24
  [2] _mapreduce
    @ ./reduce.jl:437 [inlined]
  [3] _mapreduce_dim
    @ ./reducedim.jl:337 [inlined]
  [4] mapreduce
    @ ./reducedim.jl:329 [inlined]
  [5] _sum
    @ ./reducedim.jl:987 [inlined]
  [6] sum
    @ ./reducedim.jl:983 [inlined]
  [7] #rrule#725
    @ ~/.julia/packages/ChainRules/sm2ny/src/rulesets/Base/mapreduce.jl:103 [inlined]
  [8] rrule
    @ ~/.julia/packages/ChainRules/sm2ny/src/rulesets/Base/mapreduce.jl:76 [inlined]
  [9] chain_rrule
    @ ~/.julia/packages/Zygote/3To5I/src/compiler/chainrules.jl:233 [inlined]
 [10] macro expansion
    @ ~/.julia/packages/Zygote/3To5I/src/compiler/interface2.jl:0 [inlined]
 [11] _pullback
    @ ~/.julia/packages/Zygote/3To5I/src/compiler/interface2.jl:91 [inlined]
 [12] foo
    @ ./REPL[6]:2 [inlined]
 [13] _pullback(ctx::Zygote.Context{false}, f::typeof(foo), args::Vector{Float64})
    @ Zygote ~/.julia/packages/Zygote/3To5I/src/compiler/interface2.jl:0
 [14] pullback(f::Function, cx::Zygote.Context{false}, args::Vector{Float64})
    @ Zygote ~/.julia/packages/Zygote/3To5I/src/compiler/interface.jl:96
 [15] pullback(f::Function, args::Vector{Float64})
    @ Zygote ~/.julia/packages/Zygote/3To5I/src/compiler/interface.jl:94
 [16] top-level scope
    @ REPL[7]:1

So it seems like the problem is the tuple type should be a Tangent{Tuple{...}, ...}
So Zygote isn't wrapping stuff up right before giving it to chainrules?

[ToucheSir]

The primal doesn't work either, and throws an almost identical error.

julia> foo([1., 2., 3.])
ERROR: MethodError: no method matching +(::Tuple{Float64, Float64}, ::Tuple{Float64, Float64})
The function `+` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  +(::Any, ::Any, ::Any, ::Any...)
   @ Base operators.jl:596
  +(::BitMatrix, ::LinearAlgebra.UniformScaling)
   @ LinearAlgebra .julia/juliaup/julia-1.11.3+0.x64.linux.gnu/share/julia/stdlib/v1.11/LinearAlgebra/src/uniformscaling.jl:151
  +(::Bool, ::Complex{Bool})
   @ Base complex.jl:308
  ...