From bffac95febd7a29cfac0becfcb019cd057b53765 Mon Sep 17 00:00:00 2001
From: kaizhangNV <149626564+kaizhangNV@users.noreply.github.com>
Date: Thu, 2 Oct 2025 15:23:53 -0700
Subject: Fix the missing derivative member check (#8569)

Close #8568.

The root cause of this issue is that when the struct is indirectly
inherited from IDifferentiable type, we will not check the reference of
the DerivativeMember attribute. This PR fixes this issue by checking the
DerivativeMember attribute right before synthesize the requirement
methods of IDifferentiable interface.
---
 .../autodiff/custom-differential-type-error.slang  | 26 ++++++++++++
 tests/autodiff/custom-differential-type.slang      | 46 ++++++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 tests/autodiff/custom-differential-type-error.slang
 create mode 100644 tests/autodiff/custom-differential-type.slang

(limited to 'tests/autodiff')

diff --git a/tests/autodiff/custom-differential-type-error.slang b/tests/autodiff/custom-differential-type-error.slang
new file mode 100644
index 000000000..2542eff4f
--- /dev/null
+++ b/tests/autodiff/custom-differential-type-error.slang
@@ -0,0 +1,26 @@
+//TEST:SIMPLE(filecheck=CHECK):-target spirv
+
+interface IFoo : IDifferentiable
+{
+    float myFunc();
+}
+
+struct Bar: IDifferentiable
+{
+    float y;
+}
+
+struct Foo :  IFoo
+{
+    typealias Differential = Bar;
+
+    // CHECK: ([[# @LINE+1]]): error 30027: 'x' is not a member of 'typeof(Foo.Differential)'.
+    [DerivativeMember(Differential.x)]
+    float x;
+
+    [BackwardDifferentiable]
+    float myFunc()
+    {
+        return x * x;
+    };
+}
diff --git a/tests/autodiff/custom-differential-type.slang b/tests/autodiff/custom-differential-type.slang
new file mode 100644
index 000000000..4782b4297
--- /dev/null
+++ b/tests/autodiff/custom-differential-type.slang
@@ -0,0 +1,46 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-cuda -compute -shaderobj -output-using-type
+
+interface IFoo : IDifferentiable
+{
+    float myFunc();
+}
+
+struct Bar: IDifferentiable
+{
+    float y;
+}
+
+struct Foo :  IFoo
+{
+    typealias Differential = Bar;
+
+    [DerivativeMember(Differential.y)]
+    float x;
+
+    [BackwardDifferentiable]
+    float myFunc()
+    {
+        return x * x;
+    };
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0], stride=4):out,name=g_output
+RWStructuredBuffer<float> g_output;
+
+[BackwardDifferentiable]
+float wrapper(Foo f)
+{
+    return f.myFunc();
+}
+
+[shader("compute")]
+void computeMain(uint3 thread_id : SV_DispatchThreadID)
+{
+    var di = diffPair(Foo(1.0f), Bar(0.0f));
+    bwd_diff(wrapper)(di, 1.0f);
+
+    // CHECK: 2.0
+    g_output[0] = di.d.y;
+}
-- 
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