From 3a7f89189d8e2b6b2e6514b18618245975cd2366 Mon Sep 17 00:00:00 2001
From: Oscar Dowson <odow@users.noreply.github.com>
Date: Sun, 7 Jan 2024 21:37:36 +1300
Subject: [PATCH] Fix map_indices for AbstractAutomaticDifferentiation (#2394)

---
 src/Nonlinear/types.jl      |  7 +++++++
 test/Nonlinear/Nonlinear.jl | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/Nonlinear/types.jl b/src/Nonlinear/types.jl
index ca91a9caeb..2afc67a931 100644
--- a/src/Nonlinear/types.jl
+++ b/src/Nonlinear/types.jl
@@ -184,6 +184,13 @@ An abstract type for extending [`Evaluator`](@ref).
 """
 abstract type AbstractAutomaticDifferentiation end
 
+function MOI.Utilities.map_indices(
+    ::F,
+    backend::AbstractAutomaticDifferentiation,
+) where {F<:Function}
+    return backend
+end
+
 """
     Evaluator(
         model::Model,
diff --git a/test/Nonlinear/Nonlinear.jl b/test/Nonlinear/Nonlinear.jl
index 9fcd1793aa..16b320538c 100644
--- a/test/Nonlinear/Nonlinear.jl
+++ b/test/Nonlinear/Nonlinear.jl
@@ -1147,6 +1147,22 @@ function test_unsupported_features_expr_graph_only()
     return
 end
 
+function test_automatic_differentiation_backend()
+    inner = MOI.Utilities.UniversalFallback(MOI.Utilities.Model{Float64}())
+    model = MOI.Utilities.CachingOptimizer(
+        MOI.Utilities.UniversalFallback(MOI.Utilities.Model{Float64}()),
+        MOI.Utilities.MockOptimizer(inner),
+    )
+    MOI.set(
+        model,
+        MOI.AutomaticDifferentiationBackend(),
+        MOI.Nonlinear.ExprGraphOnly(),
+    )
+    @test MOI.get(inner, MOI.AutomaticDifferentiationBackend()) ==
+          MOI.Nonlinear.ExprGraphOnly()
+    return
+end
+
 end  # TestNonlinear
 
 TestNonlinear.runtests()