feat: make dense_ad act as the identity on a dense backend (#107)

* feat: make `dense_ad` act as the identity on a dense backend

* Typo

Author: gdalle

Project.toml

@@ -1,7 +1,7 @@
 name = "ADTypes"
 uuid = "47edcb42-4c32-4615-8424-f2b9edc5f35b"
 authors = ["Vaibhav Dixit <[email protected]>, Guillaume Dalle and contributors"]
-version = "1.13.0"
+version = "1.14.0"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/sparse.jl

@@ -225,14 +225,16 @@ end
 
 """
     dense_ad(ad::AutoSparse)::AbstractADType
+    dense_ad(ad::AbstractADType)::AbstractADType
 
-Return the underlying AD package for a sparse AD choice.
+Return the underlying AD package for a sparse AD choice, act as the identity on a dense AD choice.
 
 # See also
 
   - [`AutoSparse`](@ref)
 """
 dense_ad(ad::AutoSparse) = ad.dense_ad
+dense_ad(ad::AbstractADType) = ad
 
 mode(sparse_ad::AutoSparse) = mode(dense_ad(sparse_ad))
 

test/sparse.jl

@@ -11,6 +11,7 @@
         elseif mode(ad) isa SymbolicMode
             @test mode(sparse_ad) isa SymbolicMode
         end
+        @test dense_ad(ad) == ad
         @test dense_ad(sparse_ad) == ad
         @test sparsity_detector(sparse_ad) == NoSparsityDetector()
         @test coloring_algorithm(sparse_ad) == NoColoringAlgorithm()