Fix autodiff on tensor contraction

Project.toml

@@ -19,15 +19,20 @@ UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 ValSplit = "0625e100-946b-11ec-09cd-6328dd093154"
 
 [weakdeps]
+ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a"
 Quac = "b9105292-1415-45cf-bff1-d6ccf71e6143"
+Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 
 [extensions]
+TenetChainRulesCoreExt = "ChainRulesCore"
 TenetMakieExt = "Makie"
 TenetQuacExt = "Quac"
+TenetZygoteExt = "Zygote"
 
 [compat]
 Bijections = "0.1"
+ChainRulesCore = "1.0"
 Combinatorics = "1.0"
 DeltaArrays = "0.1.1"
 EinExprs = "0.5.2"
@@ -39,4 +44,5 @@ OMEinsum = "0.7"
 Permutations = "0.4"
 Quac = "0.2"
 ValSplit = "0.1"
+Zygote = "0.6"
 julia = "1.9"

ext/TenetChainRulesCoreExt.jl

@@ -0,0 +1,18 @@
+module TenetChainRulesCoreExt
+
+using Tenet
+using ChainRulesCore
+
+ChainRulesCore.ProjectTo(tensor::T) where {T<:Tensor} =
+    ProjectTo{T}(; data = ProjectTo(tensor.data), inds = tensor.inds, meta = tensor.meta)
+
+(projector::ProjectTo{T})(dx::Union{T,Tangent{T}}) where {T<:Tensor} =
+    T(projector.data(dx.data), projector.inds; projector.meta...)
+
+function ChainRulesCore.rrule(::Type{Tensor{T,N,A}}, data, inds; meta...) where {T,N,A}
+    return Tensor(data, inds; meta...), function Tensor_pullback(_)
+        (NoTangent(), data, NoTangent())
+    end
+end
+
+end

ext/TenetZygoteExt.jl

@@ -0,0 +1,16 @@
+module TenetZygoteExt
+
+using Tenet
+using Zygote
+
+Zygote.@adjoint (T::Type{<:Tensor})(data, inds; meta...) = T(data, inds; meta...), y -> (nothing, y.data, nothing)
+
+# WARN type-piracy
+Zygote.@adjoint Base.setdiff(s, itrs...) =
+    setdiff(s, itrs...), _ -> (nothing, nothing, [nothing for _ in 1:length(itrs)]...)
+Zygote.@adjoint Base.union(s, itrs...) =
+    union(s, itrs...), _ -> (nothing, nothing, [nothing for _ in 1:length(itrs)]...)
+Zygote.@adjoint Base.intersect(s, itrs...) =
+    intersect(s, itrs...), _ -> (nothing, nothing, [nothing for _ in 1:length(itrs)]...)
+
+end