Add diagnostic for calling non-bwd-diff func from bwd-diff func. (#2602)

3 files changed, 37 insertions, 1 deletions

diff --git a/tests/diagnostics/autodiff-data-flow-2.slang b/tests/diagnostics/autodiff-data-flow-2.slang
new file mode 100644
index 000000000..aa923c5d6
--- /dev/null
+++ b/tests/diagnostics/autodiff-data-flow-2.slang
@@ -0,0 +1,28 @@
+//DIAGNOSTIC_TEST:SIMPLE:
+
+float nonDiff(float x)
+{
+    return x;
+}
+
+[ForwardDifferentiable]
+float f(float x)
+{
+    return x * x;
+}
+
+[BackwardDifferentiable]
+float g(float x)
+{
+    float val = f(x + 1); // Error: f must also be backward-differentiable
+    return val;
+}
+
+[BackwardDifferentiable]
+float h(float x)
+{
+    float val = 0;
+    // no diagnostic by clarifying intention.
+    val = no_diff(f(x + 1));
+    return val;
+}
diff --git a/tests/diagnostics/autodiff-data-flow-2.slang.expected b/tests/diagnostics/autodiff-data-flow-2.slang.expected
new file mode 100644
index 000000000..9026c0748
--- /dev/null
+++ b/tests/diagnostics/autodiff-data-flow-2.slang.expected
@@ -0,0 +1,8 @@
+result code = -1
+standard error = {
+tests/diagnostics/autodiff-data-flow-2.slang(18): error 41020: derivative cannot be propagated through call to non-backward-differentiable function `f`, use 'no_diff' to clarify intention.
+    float val = f(x + 1); // Error: f must also be backward-differentiable
+                 ^
+}
+standard output = {
+}
diff --git a/tests/diagnostics/autodiff-data-flow.slang.expected b/tests/diagnostics/autodiff-data-flow.slang.expected
index 869ce42b3..290ef974b 100644
--- a/tests/diagnostics/autodiff-data-flow.slang.expected
+++ b/tests/diagnostics/autodiff-data-flow.slang.expected
@@ -1,6 +1,6 @@
 result code = -1
 standard error = {
-tests/diagnostics/autodiff-data-flow.slang(15): error 41020: derivative cannot be propagated through call to non-differentiable function `nonDiff`, use 'no_diff' to clarify intention.
+tests/diagnostics/autodiff-data-flow.slang(15): error 41020: derivative cannot be propagated through call to non-forward-differentiable function `nonDiff`, use 'no_diff' to clarify intention.
         val = nonDiff(x * 2.0f);
                      ^
 tests/diagnostics/autodiff-data-flow.slang(22): error 41021: a differentiable function must have at least one differentiable output.