Fix an implicit cast to a base ref counted class generates a false positive.

clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp

@@ -84,6 +84,7 @@ std::optional<bool> isRefCountable(const CXXRecordDecl* R)
   if (AnyInconclusiveBase)
     return std::nullopt;
 
+  Paths.clear();
   const auto hasPublicDerefInBase =
       [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
         auto hasDerefInBase = clang::hasPublicMethodInBase(Base, "deref");

clang/test/Analysis/Checkers/WebKit/implicit-cast-to-base-class-with-deref-in-superclass.cpp

@@ -0,0 +1,30 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.webkit.UncountedCallArgsChecker -verify %s
+// expected-no-diagnostics
+
+#include "mock-types.h"
+
+class Base {
+public:
+    virtual ~Base();
+    void ref() const;
+    void deref() const;
+};
+
+class Event : public Base {
+protected:
+    explicit Event();
+};
+
+class SubEvent : public Event {
+public:
+    static Ref<SubEvent> create();
+private:
+    SubEvent() = default;
+};
+
+void someFunction(Base&);
+
+static void test()
+{
+    someFunction(SubEvent::create());
+}