[clang] [clang][dataflow] Make optional checker work for types derived from optional. (PR #84138)

[Yitzhak Mandelbaum via cfe-commits]

================
@@ -119,20 +119,28 @@ QualType getPublicType(const Expr *E) {
     return Ty;
   }
 
-  QualType Ty = getPublicType(Cast->getSubExpr());
-
-  // Is `Ty` the type of `*this`? In this special case, we can upcast to the
-  // base class even if the base is non-public.
-  bool TyIsThisType = isa<CXXThisExpr>(Cast->getSubExpr());
-
+  // Is the derived type that we're casting from the type of `*this`? In this
+  // special case, we can upcast to the base class even if the base is
+  // non-public.
+  bool CastingFromThis = isa<CXXThisExpr>(Cast->getSubExpr());
+
+  // Find the least-derived type in the path (i.e. the last entry in the list)
+  // that we can access.
+  QualType Ty;
   for (const CXXBaseSpecifier *Base : Cast->path()) {
-    if (Base->getAccessSpecifier() != AS_public && !TyIsThisType)
+    if (Base->getAccessSpecifier() != AS_public && !CastingFromThis)
       break;
     Ty = Base->getType();
----------------
ymand wrote:

optional super nit: save `&Base` instead, avoiding a call to `getType()` until after the loop.

https://github.com/llvm/llvm-project/pull/84138