test/Sema/cxx-namespace.cpp

// RUN: clang -fsyntax-only -verify %s 
namespace A { // expected-error {{error: previous definition is here}}
  int A;
  void f() { A = 0; }
}

void f() { A = 0; } // expected-error {{error: unexpected namespace name 'A': expected expression}}
int A; // expected-error {{error: redefinition of 'A' as different kind of symbol}}
class A; // expected-error {{error: redefinition of 'A' as different kind of symbol}}

class B; // expected-error {{error: previous definition is here}}
namespace B {} // expected-error {{error: redefinition of 'B' as different kind of symbol}}

void C(); // expected-error {{error: previous definition is here}}
namespace C {} // expected-error {{error: redefinition of 'C' as different kind of symbol}}