chore: set tangent to .u

Author: DhairyaLGandhi

src/concrete_solve.jl

@@ -545,12 +545,13 @@ function DiffEqBase._concrete_solve_adjoint(
             outtype = _out isa SubArray ?
                       ArrayInterface.parameterless_type(_out.parent) :
                       ArrayInterface.parameterless_type(_out)
+            Δu = Δ isa Tangent ? unthunk.(Δ.u) : Δ
             if only_end
-                eltype(Δ) <: NoTangent && return
-                if (Δ isa AbstractArray{<:AbstractArray} || Δ isa AbstractVectorOfArray) &&
-                   length(Δ) == 1 && i == 1
+                eltype(Δu) <: NoTangent && return
+                if (Δu isa AbstractArray{<:AbstractArray} || Δu isa AbstractVectorOfArray) &&
+                   length(Δu) == 1 && i == 1
                     # user did sol[end] on only_end
-                    x = Δ isa AbstractVectorOfArray ? Δ.u[1] : Δ[1]
+                    x = Δu isa AbstractVectorOfArray ? Δu[1] : Δu[1]
                     if _save_idxs isa Number
                         vx = vec(x)
                         _out[_save_idxs] .= vx[_save_idxs]
@@ -563,12 +564,12 @@ function DiffEqBase._concrete_solve_adjoint(
                 else
                     Δ isa NoTangent && return
                     if _save_idxs isa Number
-                        x = vec(Δ)
+                        x = vec(Δu)
                         _out[_save_idxs] .= adapt(outtype, @view(x[_save_idxs]))
                     elseif _save_idxs isa Colon
-                        vec(_out) .= vec(adapt(outtype, Δ))
+                        vec(_out) .= vec(adapt(outtype, Δu))
                     else
-                        x = vec(Δ)
+                        x = vec(Δu)
                         vec(@view(_out[_save_idxs])) .= adapt(outtype, @view(x[_save_idxs]))
                     end
                 end