[cxx-interop] Interpret Self as a static shorthand for FRTs

We do not have dynamic self metadata for foreign reference types.

rdar://145066864

Author: Gabor Horvath

lib/Sema/PreCheckTarget.cpp

@@ -709,7 +709,8 @@ Expr *TypeChecker::resolveDeclRefExpr(UnresolvedDeclRefExpr *UDRE,
         if (DeclContext *typeContext = DC->getInnermostTypeContext()){
           Type SelfType = typeContext->getSelfInterfaceType();
 
-          if (typeContext->getSelfClassDecl())
+          if (typeContext->getSelfClassDecl() &&
+              !typeContext->getSelfClassDecl()->isForeignReferenceType())
             SelfType = DynamicSelfType::get(SelfType, Context);
           return new (Context)
               TypeExpr(new (Context) SelfTypeRepr(SelfType, Loc));

lib/Sema/TypeCheckType.cpp

@@ -1679,6 +1679,11 @@ static SelfTypeKind getSelfTypeKind(DeclContext *dc,
   if (!typeDC->getSelfClassDecl())
     return SelfTypeKind::StaticSelf;
 
+  // For foreign reference types `Self` is a shorthand for the nominal type.
+  if (typeDC->getSelfClassDecl() &&
+      typeDC->getSelfClassDecl()->isForeignReferenceType())
+    return SelfTypeKind::StaticSelf;
+
   // In class methods, 'Self' is the DynamicSelfType and can only appear in
   // the return type.
   switch (options.getBaseContext()) {

test/Interop/Cxx/foreign-reference/extensions.swift

@@ -0,0 +1,12 @@
+// RUN: %target-run-simple-swift(-I %S/Inputs/ -Xfrontend -enable-experimental-cxx-interop -Xfrontend -disable-availability-checking -Onone)
+// REQUIRES: executable_test
+
+import ReferenceCounted
+
+extension NS.LocalCount {
+    static func g() {}
+
+    public func f() {
+        Self.g()
+    }
+}