more extra rules for static arrays

more overloads for StaticArrays

src/extra_rules.jl

@@ -172,9 +172,14 @@ function ChainRules.rrule(::DiffractorRuleConfig, ::Type{SArray{S, T, N, L}}, x:
 end
 
 function ChainRules.frule((_, ∂x), ::Type{SArray{S, T, N, L}}, x::NTuple{L,T}) where {S, T, N, L}
-    SArray{S, T, N, L}(x), SArray{S, T, N, L}(∂x.backing)
+    #TODO: we really shouldn't actually see the isa(∂x, AbstractZero) case since the frule should be called then
+    Δx = isa(∂x, AbstractZero) ? ∂x : SArray{S, T, N, L}(ChainRulesCore.backing(∂x))
+    SArray{S, T, N, L}(x), Δx
 end
 
+Base.view(t::Tangent{T}, inds) where T<:SVector = view(T(ChainRulesCore.backing(t.data)), inds)
+Base.getindex(t::Tangent{<:SVector, <:NamedTuple}, ind::Int) = ChainRulesCore.backing(t.data)[ind]
+
 function ChainRules.frule((_, ∂x), ::Type{SArray{S, T, N, L}}, x::NTuple{L,Any}) where {S, T, N, L}
     SArray{S, T, N, L}(x), SArray{S}(∂x)
 end