Make interface types non c-style in Slang2026. (#7260)

* Make interface types non c-style.

* Make Optional<T> work with autodiff and existential types.

* Fix.

* patch behind slang 2026.

* Fix warnings.

* cleanup.

* Fix tests.

* Fix.

* Fix com interface lowering.

* Add comment to test.

* regenerate command line reference

* Add test for passing `none` to autodiff function.

* Fix recording of `getDynamicObjectRTTIBytes`.

* Fix nested Optional types.

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

5 files changed, 162 insertions, 33 deletions

diff --git a/tests/autodiff/optional.slang b/tests/autodiff/optional.slang
new file mode 100644
index 000000000..a86440413
--- /dev/null
+++ b/tests/autodiff/optional.slang
@@ -0,0 +1,59 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-slang -compute -output-using-type
+//TEST(compute,vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-vk -slang -compute -output-using-type
+
+[Differentiable]
+Optional<float> sumSquare(Optional<float> a, Optional<float> b)
+{
+    if (let x = a)
+    {
+        if (let y = b)
+        {
+            return x * x + y * y;
+        }
+        else
+        {
+            return x * x;
+        }
+    }
+    else if (let y = b)
+    {
+        return y * y;
+    }
+    return none;
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+    var dpa = diffPair<Optional<float>>(3.0f, none);
+    var dpb = diffPair<Optional<float>>(4.0f, none);
+
+    bwd_diff(sumSquare)(dpa, dpb, 1.0f);
+
+    outputBuffer[0] = -1;
+
+    // CHECK: 14.0
+    if (dpa.d.hasValue && dpb.d.hasValue)
+        outputBuffer[0] = dpa.d.value + dpb.d.value;
+
+    // CHECK: 1.0
+    dpa = diffPair<Optional<float>>(3.0f, none);
+    dpb = diffPair<Optional<float>>(4.0f, none);
+    bwd_diff(sumSquare)(dpa, dpb, none);
+    if (dpa.d.value == 0.0 && dpb.d.value == 0.0)
+    {
+        outputBuffer[1] = 1.0f;
+    }
+
+     // CHECK: 100.0
+     dpa = diffPair<Optional<float>>(none, none);
+     dpb = diffPair<Optional<float>>(4.0f, none);
+     bwd_diff(sumSquare)(dpa, dpb, 1.0);
+     if (dpa.d == none)
+     {
+         outputBuffer[2] = 100.0f;
+     }
+}
\ No newline at end of file
diff --git a/tests/initializer-list/existential-is-not-c-like.slang b/tests/initializer-list/existential-is-not-c-like.slang
new file mode 100644
index 000000000..1058033c9
--- /dev/null
+++ b/tests/initializer-list/existential-is-not-c-like.slang
@@ -0,0 +1,21 @@
+// Test that in Slang 2026, it is no longer valid to default initialize an existential value.
+#lang 2026
+
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+interface IBSDF
+{
+    float3 eval(float3 wi, float3 wo);
+}
+
+struct ShaderGraph
+{
+    IBSDF bsdf_stack[8]; // Intentionally uninitialized.
+    int next_bsdf = 0; // must be zero.
+}
+
+[numthreads(1,1,1)]
+void main()
+{
+    // CHECK: ([[# @LINE+1]]): error
+    ShaderGraph sg = {};
+}
\ No newline at end of file
diff --git a/tests/language-feature/interfaces/optional-none.slang b/tests/language-feature/interfaces/optional-none.slang
new file mode 100644
index 000000000..04bb8f83e
--- /dev/null
+++ b/tests/language-feature/interfaces/optional-none.slang
@@ -0,0 +1,47 @@
+// Test that the size of an optional interface type is the same as the existential box.
+
+//TEST:SIMPLE(filecheck=CHECK): -target hlsl -conformance "Impl1:IFoo=1" -entry computeMain -profile cs_6_0
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=BUFFER): -output-using-type
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=BUFFER): -vk -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+interface IFoo
+{
+    int method();
+}
+
+//TEST_INPUT: type_conformance Impl1:IFoo = 0
+struct Impl1 : IFoo
+{
+    int data;
+    int method() { return data + 1; }
+}
+
+struct MyType
+{
+    Optional<IFoo> foo;
+}
+
+Optional<T> process<T>(Optional<T> opt)
+{
+    return opt;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    MyType t = {};
+    t.foo = process(t.foo);
+
+    // BUFFER: 100
+    if (let f = t.foo)
+        outputBuffer[0] = f.method();
+    else
+        outputBuffer[0] = 100;
+}
+
+// CHECK: struct MyType
+// CHECK-NEXT: {
+// CHECK-NEXT: Tuple{{.*}} foo{{.*}};
\ No newline at end of file
diff --git a/tests/language-feature/interfaces/zero-init-interface.slang b/tests/language-feature/interfaces/zero-init-interface.slang
deleted file mode 100644
index ed3b1eaa4..000000000
--- a/tests/language-feature/interfaces/zero-init-interface.slang
+++ /dev/null
@@ -1,33 +0,0 @@
-// Test that we can zero-init a struct with interface typed member.
-
-//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=BUFFER): -shaderobj
-//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=BUFFER): -vk -shaderobj
-
-//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
-RWStructuredBuffer<int> outputBuffer;
-
-interface IFoo
-{
-    int method();
-}
-
-//TEST_INPUT: type_conformance Impl1:IFoo = 0
-struct Impl1 : IFoo
-{
-    int data;
-    int method() { return data + 1; }
-}
-
-struct MyType
-{
-    IFoo foo;
-}
-
-
-[numthreads(1, 1, 1)]
-void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
-{
-    MyType t = {};
-    // BUFFER: 1
-    outputBuffer[0] = t.foo.method();
-}
diff --git a/tests/language-feature/nested-optional.slang b/tests/language-feature/nested-optional.slang
new file mode 100644
index 000000000..8fdeac33b
--- /dev/null
+++ b/tests/language-feature/nested-optional.slang
@@ -0,0 +1,35 @@
+//TEST:INTERPRET(filecheck=CHECK):
+
+Optional<Optional<int>> getNone() { return none; }
+
+void main()
+{
+    Optional<Optional<Optional<int>>> val = Optional<Optional<int>>(5);
+    Optional<Optional<Optional<int>>> defaultVal1 = none;
+    Optional<Optional<Optional<int>>> defaultVal2 = getNone();
+
+    // CHECK: 8
+    printf("%d\n", sizeof(val));
+
+    // CHECK: success
+    if (defaultVal1.hasValue == defaultVal2.hasValue)
+    {
+        printf("success\n");
+    }
+    else
+    {
+        printf("failure\n");
+    }
+
+    // CHECK: value: 5
+    if (let x = val)
+    {
+        if (let y = x)
+        {
+            if (let z = y)
+            {
+                printf("value: %d\n", z);
+            }
+        }
+    }
+}
\ No newline at end of file