Allow calling a generic function with an existential value (dynamic dispatch) (#1508)

* Allow calling a generic function with an existential value (dynamic dispatch).

* Fixes per review comments.

* Clean up implementation by having `openExistential` return `ExtractExistentialType` instead of a DeclRef to the interface with a `ThisTypeSubstitution`.

* More cleanups

Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/source/slang/slang-check-overload.cpp b/source/slang/slang-check-overload.cpp
index 94638e473..df5424659 100644
--- a/source/slang/slang-check-overload.cpp
+++ b/source/slang/slang-check-overload.cpp
@@ -1517,6 +1517,11 @@ namespace Slang
                 return CreateErrorExpr(expr);
         }
 
+        for (auto& arg : expr->arguments)
+        {
+            arg = maybeOpenExistential(arg);
+        }
+
         context.originalExpr = expr;
         context.funcLoc = funcExpr->loc;