Diagnose on storing differentiable value into non-differentiable location. (#2681)

2 files changed, 34 insertions, 0 deletions

diff --git a/tests/diagnostics/autodiff-data-flow-3.slang b/tests/diagnostics/autodiff-data-flow-3.slang
new file mode 100644
index 000000000..0a8e3e58a
--- /dev/null
+++ b/tests/diagnostics/autodiff-data-flow-3.slang
@@ -0,0 +1,26 @@
+//DIAGNOSTIC_TEST:SIMPLE:
+
+struct DiffT : IDifferentiable
+{
+    float f;
+}
+struct NoDiffField
+{
+    DiffT fp;
+}
+
+[BackwardDifferentiable]
+float g(float x)
+{
+    NoDiffField obj;
+    obj.fp.f = x * x; // Error, this location cannot hold derivative.
+    return obj.fp.f;
+}
+
+[BackwardDifferentiable]
+float h(float x)
+{
+    NoDiffField obj;
+    obj.fp.f = detach(x * x); // OK.
+    return obj.fp.f;
+}
diff --git a/tests/diagnostics/autodiff-data-flow-3.slang.expected b/tests/diagnostics/autodiff-data-flow-3.slang.expected
new file mode 100644
index 000000000..73381cf58
--- /dev/null
+++ b/tests/diagnostics/autodiff-data-flow-3.slang.expected
@@ -0,0 +1,8 @@
+result code = -1
+standard error = {
+tests/diagnostics/autodiff-data-flow-3.slang(16): error 41024: derivative is lost during assignment to non-differentiable location. Use 'detach()' to clarify intention.
+    obj.fp.f = x * x; // Error, this location cannot hold derivative.
+             ^
+}
+standard output = {
+}