tests are failing due to ComponentArrays

[CarloLucibello]

on a recent CI run
https://github.com/FluxML/Flux.jl/actions/runs/8411429678/job/23031003428?pr=2409#step:7:561

[CarloLucibello]

It appears that recent changes in ComponentArrays.jl have broken the parameter collection.

On ComponentArrays v0.15.10 we had

julia> using Flux, ComponentArrays

julia> w = ComponentArray(a=1.0, b=[2, 1, 4], c=(a=2, b=[1, 2]))
ComponentVector{Float64}(a = 1.0, b = [2.0, 1.0, 4.0], c = (a = 2.0, b = [1.0, 2.0]))

julia> ps = Flux.params(w)
Params([(a = 1.0, b = [2.0, 1.0, 4.0], c = (a = 2.0, b = [1.0, 2.0]))])

julia> ps[1]
ComponentVector{Float64}(a = 1.0, b = [2.0, 1.0, 4.0], c = (a = 2.0, b = [1.0, 2.0]))

julia> gs = gradient(() -> sum(w.a) + sum(w.c.b), ps)
Grads(...)

julia> gradient(() -> sum(w.a) + sum(w.c.b), ps)[ps[1]]
ComponentVector{Float64}(a = 1.0, b = [0.0, 0.0, 0.0], c = (a = 0.0, b = [1.0, 1.0]))

On ComponentArrays v0.15.11 instead

julia> w = ComponentArray(a=1.0, b=[2, 1, 4], c=(a=2, b=[1, 2]))
ComponentVector{Float64}(a = 1.0, b = [2.0, 1.0, 4.0], c = (a = 2.0, b = [1.0, 2.0]))

julia> ps = Flux.params(w)
Params([[2.0, 1.0, 4.0], [1.0, 2.0]])

julia> ps[1]
3-element Vector{Float64}:
 2.0
 1.0
 4.0

julia> gs = gradient(() -> sum(w.a) + sum(w.c.b), ps)
Grads(...)

julia> gradient(() -> sum(w.a) + sum(w.c.b), ps)[ps[1]] # nothing

Could jonniedie/ComponentArrays.jl#252 be the responsible? cc @avik-pal

[avik-pal]

https://github.com/jonniedie/ComponentArrays.jl/blob/main/src%2Fcompat%2Ffunctors.jl was added.