fix ad type instabilities in new zygote (#202)

Author: Jutho

ext/TensorOperationsChainRulesCoreExt.jl

@@ -86,19 +86,19 @@ function _rrule_tensoradd!(C, A, pA, conjA, α, β, ba)
     function pullback(ΔC′)
         ΔC = unthunk(ΔC′)
         dC = @thunk projectC(scale(ΔC, conj(β)))
-        dA = @thunk begin
+        dA = @thunk let
             ipA = invperm(linearize(pA))
             _dA = zerovector(A, VectorInterface.promote_add(ΔC, α))
             _dA = tensoradd!(_dA, ΔC, (ipA, ()), conjA, conjA ? α : conj(α), Zero(), ba...)
             return projectA(_dA)
         end
-        dα = @thunk begin
+        dα = @thunk let
             _dα = tensorscalar(tensorcontract(A, ((), linearize(pA)), !conjA,
                                               ΔC, (trivtuple(numind(pA)), ()), false,
                                               ((), ()), One(), ba...))
             return projectα(_dα)
         end
-        dβ = @thunk begin
+        dβ = @thunk let
             # TODO: consider using `inner`
             _dβ = tensorscalar(tensorcontract(C, ((), trivtuple(numind(pA))), true,
                                               ΔC, (trivtuple(numind(pA)), ()), false,
@@ -165,7 +165,7 @@ function _rrule_tensorcontract!(C, A, pA, conjA, B, pB, conjB, pAB, α, β, ba)
         pΔC = (TupleTools.getindices(ipAB, trivtuple(numout(pA))),
                TupleTools.getindices(ipAB, numout(pA) .+ trivtuple(numin(pB))))
         dC = @thunk projectC(scale(ΔC, conj(β)))
-        dA = @thunk begin
+        dA = @thunk let
             ipA = (invperm(linearize(pA)), ())
             conjΔC = conjA
             conjB′ = conjA ? conjB : !conjB
@@ -177,7 +177,7 @@ function _rrule_tensorcontract!(C, A, pA, conjA, B, pB, conjB, pAB, α, β, ba)
                                   conjA ? α : conj(α), Zero(), ba...)
             return projectA(_dA)
         end
-        dB = @thunk begin
+        dB = @thunk let
             ipB = (invperm(linearize(pB)), ())
             conjΔC = conjB
             conjA′ = conjB ? conjA : !conjA
@@ -189,15 +189,15 @@ function _rrule_tensorcontract!(C, A, pA, conjA, B, pB, conjB, pAB, α, β, ba)
                                   conjB ? α : conj(α), Zero(), ba...)
             return projectB(_dB)
         end
-        dα = @thunk begin
+        dα = @thunk let
             C_αβ = tensorcontract(A, pA, conjA, B, pB, conjB, pAB, One(), ba...)
             # TODO: consider using `inner`
             _dα = tensorscalar(tensorcontract(C_αβ, ((), trivtuple(numind(pAB))), true,
                                               ΔC, (trivtuple(numind(pAB)), ()), false,
                                               ((), ()), One(), ba...))
             return projectα(_dα)
         end
-        dβ = @thunk begin
+        dβ = @thunk let
             # TODO: consider using `inner`
             _dβ = tensorscalar(tensorcontract(C, ((), trivtuple(numind(pAB))), true,
                                               ΔC, (trivtuple(numind(pAB)), ()), false,
@@ -249,7 +249,7 @@ function _rrule_tensortrace!(C, A, p, q, conjA, α, β, ba)
     function pullback(ΔC′)
         ΔC = unthunk(ΔC′)
         dC = @thunk projectC(scale(ΔC, conj(β)))
-        dA = @thunk begin
+        dA = @thunk let
             ip = invperm((linearize(p)..., q[1]..., q[2]...))
             Es = map(q[1], q[2]) do i1, i2
                 return one(TensorOperations.tensoralloc_add(scalartype(A), A,
@@ -263,15 +263,15 @@ function _rrule_tensortrace!(C, A, p, q, conjA, α, β, ba)
                                  conjA ? α : conj(α), Zero(), ba...)
             return projectA(_dA)
         end
-        dα = @thunk begin
+        dα = @thunk let
             C_αβ = tensortrace(A, p, q, false, One(), ba...)
             _dα = tensorscalar(tensorcontract(C_αβ, ((), trivtuple(numind(p))),
                                               !conjA,
                                               ΔC, (trivtuple(numind(p)), ()), false,
                                               ((), ()), One(), ba...))
             return projectα(_dα)
         end
-        dβ = @thunk begin
+        dβ = @thunk let
             _dβ = tensorscalar(tensorcontract(C, ((), trivtuple(numind(p))), true,
                                               ΔC, (trivtuple(numind(p)), ()), false,
                                               ((), ()), One(), ba...))