Fix around extensions and `IDifferentiable` requirement synthesis. (#4729)

* Check extensions before function parameters.
Fix decl ref formation for synthesized differentiable requirements that are inside an extension.

* Fix clang errors.

* More clang fix.

* Fix warnings.

* Fix build error.

* Fix.

* Fix typo.

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/bugs/extended-type-in-param.slang b/tests/bugs/extended-type-in-param.slang
new file mode 100644
index 000000000..b3631d36e
--- /dev/null
+++ b/tests/bugs/extended-type-in-param.slang
@@ -0,0 +1,28 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+struct ArrayLike<T>
+{
+}
+__generic<T : IDifferentiable>
+extension ArrayLike<T> : IDifferentiable
+{
+}
+
+struct ExpectsDiff<T : IDifferentiable>
+{
+}
+
+// test that using `ExpectsDiff<ArrayLike<T>>` is fine to the type system.
+// this means that we must have checked the extension for `ArrayLike<T>` before
+// we check the `t3` parameter for `test`.
+void test<T : IDifferentiable>(ExpectsDiff<ArrayLike<T>> t3)
+{
+}
+
+// CHECK: OpEntryPoint
+
+[numthreads(1, 1, 1)]
+void main()
+{
+    ExpectsDiff<ArrayLike<float>> v = {};
+    test<float>(v);
+}
\ No newline at end of file