--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaCXX/namespace-alias.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,170 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+namespace N { struct X { }; };
+
+namespace A = N;
+
+int B; // expected-note {{previous definition is here}}
+namespace B = N; // expected-error {{redefinition of 'B' as different kind of symbol}}
+
+namespace C { } // expected-note {{previous definition is here}}
+namespace C = N; // expected-error {{redefinition of 'C'}}
+
+int i;
+namespace D =
+i; // expected-error {{expected namespace name}}
+
+namespace E1 = N::
+Foo; // expected-error {{expected namespace name}}
+namespace E2 = N::
+X; // expected-error {{expected namespace name}}
+
+namespace F {
+  namespace A { namespace B { } } // expected-note {{candidate found by name lookup is 'F::A::B'}}
+  namespace B { } // expected-note {{candidate found by name lookup is 'F::B'}}
+  using namespace A;
+  namespace D = B; // expected-error {{reference to 'B' is ambiguous}}
+}
+
+namespace G { 
+  namespace B = N;
+}
+
+namespace H {
+  namespace A1 { }
+  namespace A2 { }
+
+  // These all point to A1.
+  namespace B = A1;
+  namespace B = A1;
+  namespace C = B;
+  namespace B = C; // expected-note {{previously defined as an alias for 'A1'}}
+
+  namespace B = A2; // expected-error {{redefinition of 'B' as an alias for a different namespace}}
+}
+
+namespace I { 
+  namespace A1 { int i; }
+  
+  namespace A2 = A1;
+}
+
+int f() {
+  return I::A2::i;
+}
+
+namespace J {
+  namespace A { 
+    namespace B { void func (); }
+  }
+
+  namespace C = A;
+
+  using namespace C::B;
+
+  void g() {
+    func();
+  }
+}
+
+namespace K {
+  namespace KA { void func(); }
+
+  void f() {
+    namespace KB = KA;
+    KB::func();
+  }
+
+  template <class T> void g() {
+    namespace KC = KA;
+    KC::func();
+  }
+  template void g<int>();
+  template void g<long>();
+
+  void h() {
+    KB::func(); // expected-error {{undeclared identifier 'KB'}}
+    KC::func(); // expected-error {{undeclared identifier 'KC'}}
+  }
+}
+
+namespace {
+  class C1;
+}
+namespace {
+  class C1;
+}
+C1 *pc1 = 0;
+
+namespace N {
+  namespace {
+    class C2;
+  }
+}
+namespace N {
+  namespace {
+    class C2;
+  }
+}
+N::C2 *pc2 = 0;
+
+// PR6341
+namespace A = N;
+namespace N { }
+namespace A = N;
+
+A::X nx;
+
+namespace PR7014 {
+  namespace X
+  {
+    namespace Y {}
+  }
+
+  using namespace X;
+
+  namespace Y = X::Y;
+}
+
+namespace PR25731 {
+  void f() {
+    namespace X = PR25731;
+    namespace X = PR25731;
+    X::f();
+  }
+}
+
+namespace MultipleUnambiguousLookupResults {
+  namespace A { int y; }
+  namespace B {
+    namespace X { int x; }
+    namespace Y = A;
+    namespace Z = A; // expected-note {{candidate}}
+  }
+  namespace C {
+    namespace X = B::X;
+    namespace Y = A;
+    namespace Z = X; // expected-note {{candidate}}
+  }
+  using namespace B;
+  using namespace C;
+  int x1 = X::x; // ok, unambiguous
+  int y1 = Y::y; // ok, unambiguous
+  int z1 = Z::x; // expected-error {{ambiguous}}
+
+  namespace X = C::X;
+  namespace Y = A;
+  int x2 = X::x; // ok, unambiguous
+  int y2 = Y::y; // ok, unambiguous
+}
+
+namespace RedeclOfNonNamespace {
+  int a; // expected-note {{previous}}
+  namespace X { int b; }
+  using X::b; // expected-note {{previous}}
+  namespace c {} // expected-note {{previous}}
+
+  namespace a = X; // expected-error {{different kind}}
+  namespace b = X; // expected-error {{different kind}}
+  namespace c = X; // expected-error-re {{redefinition of 'c'{{$}}}}
+}