Corrects bug in the DiagonalTensorMap rrule, adds

tests for the new code, adds a proper generator of
random tangents for DiagonalTensorMap

ext/TensorKitChainRulesCoreExt/constructors.jl

@@ -12,9 +12,10 @@ function ChainRulesCore.rrule(::Type{<:TensorMap}, d::DenseArray, args...; kwarg
     return TensorMap(d, args...; kwargs...), TensorMap_pullback
 end
 
-function ChainRulesCore.rrule(::Type{<:DiagonalTensorMap}, d::DenseVector, args...; kwargs...)
-    D=TensorMap(d, args...; kwargs...)
-    project_D=ProjectTo(D)
+function ChainRulesCore.rrule(::Type{<:DiagonalTensorMap}, d::DenseVector, args...;
+                              kwargs...)
+    D = DiagonalTensorMap(d, args...; kwargs...)
+    project_D = ProjectTo(D)
     function DiagonalTensorMap_pullback(Δt)
         ∂d = project_D(unthunk(Δt)).data
         return NoTangent(), ∂d, ntuple(_ -> NoTangent(), length(args))...

test/ad.jl

@@ -15,6 +15,9 @@ end
 function ChainRulesTestUtils.rand_tangent(rng::AbstractRNG, x::AbstractTensorMap)
     return randn!(similar(x))
 end
+function ChainRulesTestUtils.rand_tangent(rng::AbstractRNG, x::DiagonalTensorMap)
+    return DiagonalTensorMap(randn(eltype(x), dim(x.domain)), x.domain)
+end
 ChainRulesTestUtils.rand_tangent(::AbstractRNG, ::VectorSpace) = NoTangent()
 function ChainRulesTestUtils.test_approx(actual::AbstractTensorMap,
                                          expected::AbstractTensorMap, msg=""; kwargs...)
@@ -144,6 +147,20 @@ Vlist = ((ℂ^2, (ℂ^3)', ℂ^3, ℂ^2, (ℂ^2)'),
                    fkwargs=(; tol=Inf))
     end
 
+    @timedtestset "Basic utility (DiagonalTensor)" begin
+        for NumType in [Float64, ComplexF64]
+            for v in V
+                T1 = DiagonalTensorMap(randn(NumType, dim(v)), v)
+                T2 = TensorMap(T1)
+
+                P1 = ProjectTo(T1)
+                @test P1(T2) == T1
+
+                test_rrule(DiagonalTensorMap, T1.data, T1.domain)
+            end
+        end
+    end
+
     @timedtestset "Basic Linear Algebra with scalartype $T" for T in (Float64, ComplexF64)
         A = randn(T, V[1] ⊗ V[2] ← V[3] ⊗ V[4] ⊗ V[5])
         B = randn(T, space(A))