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, 4 insertions, 0 deletions

diff --git a/source/slang/slang-lookup.cpp b/source/slang/slang-lookup.cpp
index c9b922415..a17ba0ba2 100644
--- a/source/slang/slang-lookup.cpp
+++ b/source/slang/slang-lookup.cpp
@@ -587,6 +587,10 @@ static void _lookUpMembersInSuperTypeImpl(
 
         _lookUpMembersInSuperTypeDeclImpl(astBuilder, name, leafType, superType, leafIsSuperWitness, declRef, request, ioResult, inBreadcrumbs);
     }
+    if (auto extractExistentialType = as<ExtractExistentialType>(superType))
+    {
+        _lookUpMembersInSuperTypeDeclImpl(astBuilder, name, leafType, superType, leafIsSuperWitness, extractExistentialType->interfaceDeclRef, request, ioResult, inBreadcrumbs);
+    }
 }
 
     /// Perform lookup for `name` in the context of `type`.