Add a missing dispatch (#204)

Author: ChrisRackauckas

Project.toml

@@ -8,6 +8,7 @@ ArrayInterface = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+Functors = "d9f16b24-f501-4c13-a1f2-28368ffc5196"
 GPUArrays = "0c68f7d7-f131-5f86-a1c3-88cf8149b2d7"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 RecursiveArrayTools = "731186ca-8d62-57ce-b412-fbd966d074cd"
@@ -23,6 +24,7 @@ ChainRulesCore = "0.8, 0.9, 0.10, 1"
 ConstructionBase = "1"
 GPUArrays = "8"
 ForwardDiff = "0.10"
+Functors = "0.4.4"
 Requires = "1"
 ReverseDiff = "1"
 RecursiveArrayTools = "2"

src/ComponentArrays.jl

@@ -1,7 +1,7 @@
 module ComponentArrays
 
 import ChainRulesCore
-import StaticArrayInterface, ArrayInterface
+import StaticArrayInterface, ArrayInterface, Functors
 
 using LinearAlgebra
 

src/compat/chainrulescore.jl

@@ -17,3 +17,8 @@ function ChainRulesCore.ProjectTo(ca::ComponentArray)
 end
 
 (p::ChainRulesCore.ProjectTo{ComponentArray})(dx::AbstractArray) = ComponentArray(p.project(dx), p.axes)
+
+function (p::ChainRulesCore.ProjectTo{ComponentArray})(t::ChainRulesCore.Tangent{A, <:NamedTuple}) where {A}
+    nt = Functors.fmap(ChainRulesCore.backing, ChainRulesCore.backing(t))
+    return ComponentArray(nt)
+end

test/Project.toml

@@ -2,6 +2,7 @@
 ArrayInterfaceCore = "30b0a656-2188-435a-8636-2ec0e6a096e2"
 FiniteDiff = "6a86dc24-6348-571c-b903-95158fe2bd41"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+Functors = "d9f16b24-f501-4c13-a1f2-28368ffc5196"
 InvertedIndices = "41ab1584-1d38-5bbf-9106-f11c6c58b48f"
 JLArrays = "27aeb0d3-9eb9-45fb-866b-73c2ecf80fcb"
 LabelledArrays = "2ee39098-c373-598a-b85f-a56591580800"