fix nothing in mutable struct getindex/getfield

src/lib/lib.jl

@@ -107,7 +107,7 @@ using Base: tail
 @adjoint function literal_getindex(xs::NTuple{N,Any}, ::Val{i}) where {N,i}
   val = xs[i]
   function back(Δ)
-    accum_param(__context__, val, Δ) === nothing && return
+    accum_param(__context__, val, Δ)
     return ntuple(j -> i == j ? Δ : nothing, Val(N)), nothing
   end
   val, back
@@ -116,7 +116,7 @@ end
 @adjoint function getindex(xs::NTuple{N,Any}, i::Integer) where N
   val = xs[i]
   function back(Δ)
-    accum_param(__context__, val, Δ) === nothing && return
+    accum_param(__context__, val, Δ)
     return ntuple(j -> i == j ? Δ : nothing, Val(N)), nothing
   end
   return val, back
@@ -228,8 +228,8 @@ end
 
 @adjoint function literal_getfield(x, ::Val{f}) where f
   val = getfield(x, f)
-  function back(Δ)
-    accum_param(__context__, val, Δ) === nothing && return
+  function literal_getfield_back(Δ)
+    accum_param(__context__, val, Δ)
     if isimmutable(x)
       dx = (; nt_nothing(x)..., pair(Val(f), Δ, x)...)
       (_project(x, dx), nothing)
@@ -239,7 +239,7 @@ end
       return (dx,nothing)
     end
   end
-  unwrap(val), back
+  unwrap(val), literal_getfield_back
 end
 
 _pullback(cx::AContext, ::typeof(getfield), x, field_name::Symbol) =

test/features.jl

@@ -476,7 +476,7 @@ end
   @test_broken gradient(x -> abs2(x[1].x) + 7 * x[1].x.re, [Ref(1+im)]) == ([(x = 9.0 + 2.0im,)],)
   @test_broken gradient(x -> abs2(x[1].x) + 7 * real(x[1].x), [Ref(1+im)]) == ([(x = 9.0 + 2.0im,)],)  # worked on 0.6.0, 0.6.20
 
-  @test_broken gradient(x -> abs2(x[].x) + 7 * real(x[].x), Ref(Ref(1+im))) == ((x = 9.0 + 2.0im,),)  # gives nothing, same in 0.6.0
+  @test gradient(x -> abs2(x[].x) + 7 * real(x[].x), Ref(Ref(1+im))) == ((x = (x = 9.0 + 2.0im,),),)  # gave `nothing` from 0.6.0 to 0.6.41
 
   # Array of mutables:
   @test gradient(x -> sum(getindex.(x).^2), Ref.(1:3))[1] == [(;x=2i) for i in 1:3]
@@ -490,6 +490,61 @@ end
   @test gradient(x -> sum(sum, Ref(x) .* [1,2,3]), [4,5]) == ([6.0, 6.0],)
 end
 
+@testset "mutable accum_param bugs" begin
+
+  mutable struct Mut{T}; x::T; end
+  struct Imm{T}; x::T; end
+
+  # Indexing a tuple containing a mutable struct gave `nothing`
+  x1 = (Mut(3.0),)
+  x2 = (Imm(3.0),)
+  x3 = (Ref(3.0),)
+  @test gradient(x -> x[1].x^2, x1)[1] == ((x = 6.0,),)  # fails on v0.6.0 v0.6.41
+  @test gradient(x -> x[1].x^2, x2)[1] == ((x = 6.0,),)
+  @test gradient(x -> x[1].x^2, x3)[1] == ((x = 6.0,),)  # fails on v0.6.0 v0.6.41
+  i1 = 1
+  @test gradient(x -> x[i1].x^2, x1)[1] == ((x = 6.0,),)  # fails on v0.6.0 v0.6.41
+  @test gradient(x -> x[i1].x^2, x2)[1] == ((x = 6.0,),)
+  @test gradient(x -> x[i1].x^2, x3)[1] == ((x = 6.0,),)  # fails on v0.6.0 v0.6.41
+
+  @test gradient(x -> x[1][1].x^2, [x1])[1] == [((x = 6.0,),)]  # fails on v0.6.0 v0.6.41
+  @test gradient(x -> x[1][1].x^2, [x2])[1] == [((x = 6.0,),)]
+  @test gradient(x -> x[1][1].x^2, [x3])[1] == [((x = 6.0,),)]  # fails on v0.6.0 v0.6.41
+
+  # When `getfield` returns a mutable struct, it gave `nothing`:
+  x4 = Imm(Mut(4.0))
+  x5 = Mut(Mut(4.0))
+  x6 = Imm(Imm(4.0))
+  @test gradient(x -> x.x.x^3, x4)[1] == (x = (x = 48.0,),)  # fails on v0.6.0 v0.6.41
+  @test gradient(x -> x.x.x^3, x5)[1] == (x = (x = 48.0,),)  # fails on v0.6.0
+  @test gradient(x -> x.x.x^3, x6)[1] == (x = (x = 48.0,),)  # fails on v0.6.41
+
+  @test gradient(x -> x[2].x.x^3, [x4, x4])[1] == [nothing, (x = (x = 48.0,),)]  # fails on v0.6.0 v0.6.41
+  @test gradient(x -> x[2].x.x^3, [x4, x5])[1] == [nothing, (x = (x = 48.0,),)]  # fails on v0.6.0
+  @test gradient(x -> x[2].x.x^3, [x4, x6])[1] == [nothing, (x = (x = 48.0,),)]  # fails on v0.6.41
+
+  # Check when using implicit parameters, Params cases used to pass:
+  y1 = [3.0]
+  y2 = (Mut(y1),)
+  y3 = (Imm(y1),)
+  @test gradient(x -> sum(x[1].x)^2, y2)[1] == ((x = [6.0],),)  # fails on v0.6.0 v0.6.41
+  @test gradient(() -> sum(y2[1].x)^2, Params([y1]))[y1] == [6.0]
+  @test gradient(x -> sum(x[1].x)^2, y3)[1] == ((x = [6.0],),)
+  @test gradient(() -> sum(y3[1].x)^2, Params([y1]))[y1] == [6.0]
+
+  @test gradient(x -> sum(x[1].x .+ x[1].x)^3, y2)[1] == ((x = [216.0],),)  # fails on v0.6.0 v0.6.41
+  @test gradient(() -> sum(y2[1].x .+ y2[1].x)^3, Params([y1]))[y1] == [216.0]
+  @test gradient(x -> sum(x[1].x .+ x[1].x)^3, y3)[1] == ((x = [216.0],),)
+  @test gradient(() -> sum(y3[1].x .+ y3[1].x)^3, Params([y1]))[y1] == [216.0]
+
+  i1 = 1
+  @test gradient(x -> sum(x[i1].x .+ x[1].x)^3, y2)[1] == ((x = [216.0],),)  # fails on v0.6.0 v0.6.41
+  @test gradient(() -> sum(y2[i1].x .+ y2[1].x)^3, Params([y1]))[y1] == [216.0]
+  @test gradient(x -> sum(x[i1].x .+ x[1].x)^3, y3)[1] == ((x = [216.0],),)
+  @test gradient(() -> sum(y3[i1].x .+ y3[1].x)^3, Params([y1]))[y1] == [216.0]
+
+end
+
 @testset "NamedTuples" begin
   @test gradient(x -> x.a, (a=1, b=2)) == ((a = 1, b = nothing),)
   @test gradient(x -> x[1].a, [(a=1, b=2)]) == ([(a = 1, b = nothing)],)