1 files changed, 40 insertions, 0 deletions
diff --git a/clang/test/SemaCXX/ext_ms_downcast.cpp b/clang/test/SemaCXX/ext_ms_downcast.cpp
new file mode 100644
index 00000000000..42feeb4b8cf
--- /dev/null
+++ b/clang/test/SemaCXX/ext_ms_downcast.cpp
@@ -0,0 +1,40 @@
+// RUN: %clang_cc1 -fsyntax-only -fms-compatibility -verify %s
+// RUN: %clang_cc1 -fsyntax-only -DNO_MS_COMPATIBILITY -verify %s
+
+// Minimal reproducer.
+class A {};
+class B : A {}; // expected-note 2 {{implicitly declared private here}}
+
+B* foo(A* p) {
+  return static_cast<B*>(p);
+#ifdef NO_MS_COMPATIBILITY
+  // expected-error@-2 {{cannot cast private base class 'A' to 'B'}}
+#else
+  // expected-warning@-4 {{casting from private base class 'A' to derived class 'B' is a Microsoft extension}}
+#endif
+}
+
+A* bar(B* p) {
+  return static_cast<A*>(p); // expected-error {{cannot cast 'B' to its private base class 'A'}}
+}
+
+// from atlframe.h
+template <class T>
+class CUpdateUI {
+public:
+  CUpdateUI() {
+    T* pT = static_cast<T*>(this);
+#ifdef NO_MS_COMPATIBILITY
+    // expected-error@-2 {{cannot cast private base class}}
+#else
+    // expected-warning@-4 {{casting from private base class 'CUpdateUI<CMDIFrame>' to derived class 'CMDIFrame' is a Microsoft extension}}
+#endif
+  }
+};
+
+// from sample WTL/MDIDocVw (mainfrm.h
+class CMDIFrame : CUpdateUI<CMDIFrame> {};
+// expected-note@-1 {{implicitly declared private here}}
+// expected-note@-2 {{in instantiation of member function}}
+
+CMDIFrame wndMain;