Fix getindex rule with AxisArrays (but break existing tests?)

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.61.0"
+version = "1.61.1"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
@@ -20,6 +20,7 @@ SuiteSparse = "4607b0f0-06f3-5cda-b6b1-a6196a1729e9"
 
 [compat]
 Adapt = "3.4.0, 4"
+AxisArrays = "0.4.7"
 ChainRulesCore = "1.20"
 ChainRulesTestUtils = "1.5"
 Compat = "3.46, 4.2"
@@ -41,6 +42,7 @@ SuiteSparse = "1"
 julia = "1.6"
 
 [extras]
+AxisArrays = "39de3d68-74b9-583c-8d2d-e117c070f3a9"
 ChainRulesTestUtils = "cdddcdb0-9152-4a09-a978-84456f9df70a"
 FiniteDifferences = "26cc04aa-876d-5657-8c51-4c34ba976000"
 JLArrays = "27aeb0d3-9eb9-45fb-866b-73c2ecf80fcb"
@@ -50,4 +52,4 @@ StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["ChainRulesTestUtils", "FiniteDifferences", "JLArrays", "JuliaInterpreter", "Random", "StaticArrays", "Test"]
+test = ["AxisArrays", "ChainRulesTestUtils", "FiniteDifferences", "JLArrays", "JuliaInterpreter", "Random", "StaticArrays", "Test"]

src/rulesets/Base/indexing.jl

@@ -125,21 +125,21 @@ Base.:(+)(oe1::OneElement, oe2::OneElement) = +(collect(oe1), oe2)
 This returns roughly `dx = zero(x)`, except that this is guaranteed to be mutable via `similar`,
 and its element type is wide enough to allow `setindex!(dx, dy, inds...)`, which is exactly what
 `∇getindex` does next.
-
-It's unfortunate to close over `x`, but `similar(typeof(x), axes(x))` doesn't
-allow `eltype(dy)`, nor does it work for many structured matrices.
 """
-_setindex_zero(x::AbstractArray{<:Number}, dy, inds::Integer...) = fill!(similar(x, typeof(dy), axes(x)), false)
-_setindex_zero(x::AbstractArray{<:Number}, dy, inds...) = fill!(similar(x, eltype(dy), axes(x)), false)
+_setindex_zero(x::AbstractArray{<:Number}, dy, inds::Integer...) =
+    fill!(similar(x, typeof(dy)), false)
+function _setindex_zero(x::AbstractArray{<:Number}, dy, inds...)
+    return fill!(similar(x, eltype(dy)), false)
+end
 function _setindex_zero(x::AbstractArray, dy, inds::Integer...)
     # This allows for types which don't define zero (like Vector) and types whose zero special (like Tangent),
     # but always makes an abstract type. TODO: make it infer concrete type for e.g. vectors of SVectors
     T = Union{typeof(dy), ZeroTangent}
-    return fill!(similar(x, T, axes(x)), ZeroTangent())
+    return fill!(similar(x, T), ZeroTangent())
 end
 function _setindex_zero(x::AbstractArray, dy, inds...)
     T = Union{eltype(dy), ZeroTangent}
-    return fill!(similar(x, T, axes(x)), ZeroTangent())
+    return fill!(similar(x, T), ZeroTangent())
 end
 ChainRules.@non_differentiable _setindex_zero(x::AbstractArray, dy::Any, inds::Any...)
 

test/rulesets/Base/indexing.jl

@@ -128,6 +128,13 @@ end
         @test dx23[3] == dxfix[3]
     end
 
+    @testset "getindex(::AxisArray{<:Number})" begin
+        X = randn((2, 3))
+        A = AxisArray(X; row=[:a, :b], col=[:x, :y, :z])
+        dA, back = rrule(getindex, A, [:a], [:x, :z])
+        unthunk(back(ones(1, 2))[2]) == [1.0 0.0 1.0; 0.0 0.0 0.0]
+    end
+
     @testset "second derivatives: ∇getindex" begin
         @eval using ChainRules: ∇getindex
         # Forward, scalar result

test/runtests.jl

@@ -3,6 +3,7 @@ using Test, ChainRulesCore, ChainRulesTestUtils
 @nospecialize
 
 using Adapt
+using AxisArrays
 using Base.Broadcast: broadcastable
 using ChainRules
 using ChainRules: stack