Add direct SArray dispatch

Author: avik-pal

src/highlevel/common.jl

@@ -332,14 +332,3 @@ init_jacobian(J::SparseMatrixCSC, ::Type{T}, fx, x; kwargs...) where {T} = T.(J)
 
 __maybe_copy_x(_, x) = x
 __maybe_copy_x(_, ::Nothing) = nothing
-
-# Create a mutable version of the input array
-function __make_mutable(x)
-    if ArrayInterface.can_setindex(x)
-        return x
-    else
-        y = similar(x)
-        copyto!(y, x)
-        return y
-    end
-end

src/highlevel/finite_diff.jl

@@ -10,7 +10,6 @@ __getfield(c::FiniteDiffJacobianCache, ::Val{:jac_prototype}) = c.jac_prototype
 
 function sparse_jacobian_cache(fd::Union{AutoSparseFiniteDiff, AutoFiniteDiff},
         sd::AbstractMaybeSparsityDetection, f::F, x; fx = nothing) where {F}
-    x = __make_mutable(x) # FiniteDiff is bad at handling immutables
     coloring_result = sd(fd, f, x)
     fx = fx === nothing ? similar(f(x)) : fx
     if coloring_result isa NoMatrixColoring
@@ -26,7 +25,6 @@ end
 
 function sparse_jacobian_cache(fd::Union{AutoSparseFiniteDiff, AutoFiniteDiff},
         sd::AbstractMaybeSparsityDetection, f!::F, fx, x) where {F}
-    x = __make_mutable(x) # FiniteDiff is bad at handling immutables
     coloring_result = sd(fd, f!, fx, x)
     if coloring_result isa NoMatrixColoring
         cache = FiniteDiff.JacobianCache(x, fx)
@@ -50,3 +48,7 @@ function sparse_jacobian!(J::AbstractMatrix, _, cache::FiniteDiffJacobianCache,
     FiniteDiff.finite_difference_jacobian!(J, f!, x, cache.cache)
     return J
 end
+
+function sparse_jacobian_static_array(_, cache::FiniteDiffJacobianCache, f, x::SArray)
+    return FiniteDiff.finite_difference_jacobian(f, x, cache.cache)
+end