Add `none` literal that is convertible to `Optional`. (#2356)

* Add `none` literal that is convertible to `Optional`.

* Fix cpu code gen.

* Include vk and cpu test for is-as operator test.

* Inline comparison operators.

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index 6290acbd9..4bcf07b2b 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -773,13 +773,28 @@ namespace Slang
         {
             if (outCost)
             {
-                *outCost = kConversionCost_None;
+                *outCost = kConversionCost_NullPtrToPtr;
             }
             if (outToExpr)
                 *outToExpr = fromExpr;
             return true;
         }
-
+        // none_t can be cast into any Optional<T> type.
+        if (as<NoneType>(fromType) && as<OptionalType>(toType))
+        {
+            if (outCost)
+            {
+                *outCost = kConversionCost_NoneToOptional;
+            }
+            if (outToExpr)
+            {
+                auto resultExpr = getASTBuilder()->create<MakeOptionalExpr>();
+                resultExpr->loc = fromExpr->loc;
+                resultExpr->type = toType;
+                *outToExpr = resultExpr;
+            }
+            return true;
+        }
         // If we are casting to an interface type, then that will succeed
         // if the "from" type conforms to the interface.
         //