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fix: handle ZeroTangent/AbstractZero in RecursiveArrayToolsZygoteExt adjoint #606

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Merged
ChrisRackauckas merged 1 commit into from
Jun 6, 2026
Merged

fix: handle ZeroTangent/AbstractZero in RecursiveArrayToolsZygoteExt adjoint #606

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7 changes: 4 additions & 3 deletions ext/RecursiveArrayToolsZygoteExt.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ using RecursiveArrayTools

using Zygote
using Zygote: FillArrays, ChainRulesCore, literal_getproperty, @adjoint
using Zygote.ChainRulesCore: AbstractZero

function ChainRulesCore.rrule(
T::Type{<:RecursiveArrayTools.GPUArraysCore.AbstractGPUArray},
Expand Down Expand Up @@ -90,23 +91,23 @@ end

function vofa_u_adjoint(d, A::RecursiveArrayTools.AbstractVectorOfArray)
m = map(enumerate(d)) do (idx, d_i)
isnothing(d_i) && return zero(A.u[idx])
(isnothing(d_i) || d_i isa AbstractZero) && return zero(A.u[idx])
d_i
end
return VectorOfArray(m)
end

function vofa_u_adjoint(d, A::RecursiveArrayTools.AbstractDiffEqArray)
m = map(enumerate(d)) do (idx, d_i)
isnothing(d_i) && return zero(A.u[idx])
(isnothing(d_i) || d_i isa AbstractZero) && return zero(A.u[idx])
d_i
end
return DiffEqArray(m, A.t)
end

@adjoint function literal_getproperty(A::ArrayPartition, ::Val{:x})
function literal_ArrayPartition_x_adjoint(d)
(ArrayPartition((isnothing(d[i]) ? zero(A.x[i]) : d[i] for i in 1:length(d))...),)
(ArrayPartition((isnothing(d[i]) || d[i] isa AbstractZero ? zero(A.x[i]) : d[i] for i in 1:length(d))...),)
end
A.x, literal_ArrayPartition_x_adjoint
end
Expand Down
19 changes: 19 additions & 0 deletions test/adjoints.jl
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
using RecursiveArrayTools, Zygote, ForwardDiff, ReverseDiff, Test
using Zygote: ChainRulesCore

function loss(x)
return sum(abs2, Array(VectorOfArray([x .* i for i in 1:5])))
Expand Down Expand Up @@ -99,3 +100,21 @@ end
let g = ReverseDiff.gradient(x -> sum(VectorOfArray([VectorOfArray([x])])), float.(1:3))
@test g ≈ ones(3)
end

# A `ZeroTangent`/`AbstractZero` slice in the cotangent (structural zero gradient)
# must be treated like an absent gradient instead of erroring on `size(::ZeroTangent)`.
let ext = Base.get_extension(RecursiveArrayTools, :RecursiveArrayToolsZygoteExt)
voa = VectorOfArray([Float64[i, i, i] for i in 1:3])
dea = DiffEqArray([Float64[i, i, i] for i in 1:3], 1:3)
d = Any[Float64[1, 1, 1], ChainRulesCore.ZeroTangent(), Float64[3, 3, 3]]
expected = [Float64[1, 1, 1], Float64[0, 0, 0], Float64[3, 3, 3]]

g_voa = ext.vofa_u_adjoint(d, voa)
@test g_voa isa VectorOfArray
@test g_voa.u == expected

g_dea = ext.vofa_u_adjoint(d, dea)
@test g_dea isa DiffEqArray
@test g_dea.u == expected
@test g_dea.t == dea.t
end
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