From ddf0d12c06e9afc7777d83777f6537bdb214757c Mon Sep 17 00:00:00 2001
From: Aayush Sabharwal <aayush.sabharwal@gmail.com>
Date: Wed, 26 Feb 2025 22:08:02 +0530
Subject: [PATCH] feat: mark `getproperty(::AbstractSystem, ::Symbol)` as
 non-differentiable

---
 ext/MTKChainRulesCoreExt.jl |  2 ++
 test/extensions/ad.jl       | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/ext/MTKChainRulesCoreExt.jl b/ext/MTKChainRulesCoreExt.jl
index f153ee77de..9cf17d203d 100644
--- a/ext/MTKChainRulesCoreExt.jl
+++ b/ext/MTKChainRulesCoreExt.jl
@@ -103,4 +103,6 @@ function ChainRulesCore.rrule(
     newbuf, pullback
 end
 
+ChainRulesCore.@non_differentiable Base.getproperty(sys::MTK.AbstractSystem, x::Symbol)
+
 end
diff --git a/test/extensions/ad.jl b/test/extensions/ad.jl
index 0e72b2b7b7..adaf6117c6 100644
--- a/test/extensions/ad.jl
+++ b/test/extensions/ad.jl
@@ -124,3 +124,13 @@ fwd, back = ChainRulesCore.rrule(remake_buffer, sys, ps, idxs, vals)
     nsol = solve(nprob, NewtonRaphson())
     @test nsol[1] ≈ 10.0 / 1.0 + 9.81 * 1.0 / 2 # anal free fall solution is y = v0*t - g*t^2/2 -> v0 = y/t + g*t/2
 end
+
+@testset "`sys.var` is non-differentiable" begin
+    @variables x(t)
+    @mtkbuild sys = ODESystem(D(x) ~ x, t)
+    prob = ODEProblem(sys, [x => 1.0], (0.0, 1.0))
+
+    grad = Zygote.gradient(prob) do prob
+        prob[sys.x]
+    end
+end