--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaTemplate/instantiate-self.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,172 @@
+// RUN: %clang_cc1 -std=c++1z -verify -pedantic-errors %s
+
+// Check that we deal with cases where the instantiation of a class template
+// recursively requires the instantiation of the same template.
+namespace test1 {
+  template<typename T> struct A {
+    struct B { // expected-note {{not complete until the closing '}'}}
+      B b; // expected-error {{has incomplete type 'test1::A<int>::B'}}
+    };
+    B b; // expected-note {{in instantiation of}}
+  };
+  A<int> a; // expected-note {{in instantiation of}}
+}
+
+namespace test2 {
+  template<typename T> struct A {
+    struct B {
+      struct C {};
+      char c[1 + C()]; // expected-error {{invalid operands to binary expression}}
+      friend constexpr int operator+(int, C) { return 4; }
+    };
+    B b; // expected-note {{in instantiation of}}
+  };
+  A<int> a; // expected-note {{in instantiation of}}
+}
+
+namespace test3 {
+  // PR12317
+  template<typename T> struct A {
+    struct B {
+      enum { Val = 1 };
+      char c[1 + Val]; // ok
+    };
+    B b;
+  };
+  A<int> a;
+}
+
+namespace test4 {
+  template<typename T> struct M { typedef int type; };
+  template<typename T> struct A {
+    struct B { // expected-note {{not complete until the closing '}'}}
+      int k[typename A<typename M<T>::type>::B().k[0] + 1]; // expected-error {{incomplete type}}
+    };
+    B b; // expected-note {{in instantiation of}}
+  };
+  A<int> a; // expected-note {{in instantiation of}}
+}
+
+// PR12298: Recursive constexpr function template instantiation leads to
+// stack overflow.
+namespace test5 {
+  template<typename T> struct A {
+    constexpr T f(T k) { return g(k); }
+    constexpr T g(T k) {
+      return k ? f(k-1)+1 : 0;
+    }
+  };
+  constexpr int x = A<int>().f(5); // ok
+}
+
+namespace test6 {
+  template<typename T> constexpr T f(T);
+  template<typename T> constexpr T g(T t) {
+    typedef int arr[f(T())]; // expected-error {{variable length array}}
+    return t;
+  }
+  template<typename T> constexpr T f(T t) {
+    typedef int arr[g(T())]; // expected-error {{zero size array}} expected-note {{instantiation of}}
+    return t;
+  }
+  int n = f(0); // expected-note 2{{instantiation of}}
+}
+
+namespace test7 {
+  template<typename T> constexpr T g(T t) {
+    return t;
+  }
+  template<typename T> constexpr T f(T t) {
+    typedef int arr[g(T() + 1)];
+    return t;
+  }
+  int n = f(0);
+}
+
+namespace test8 {
+  template<typename T> struct A {
+    int n = A{}.n; // expected-error {{default member initializer for 'n' uses itself}} expected-note {{instantiation of default member init}}
+  };
+  A<int> ai = {}; // expected-note {{instantiation of default member init}}
+}
+
+namespace test9 {
+  template<typename T> struct A { enum class B; };
+  // FIXME: It'd be nice to give the "it has not yet been instantiated" diagnostic here.
+  template<typename T> enum class A<T>::B { k = A<T>::B::k2, k2 = k }; // expected-error {{no member named 'k2'}}
+  auto k = A<int>::B::k; // expected-note {{in instantiation of}}
+}
+
+namespace test10 {
+  template<typename T> struct A {
+    void f() noexcept(noexcept(f())); // expected-error {{exception specification of 'f' uses itself}} expected-note {{instantiation of}}
+  };
+  bool b = noexcept(A<int>().f()); // expected-note {{instantiation of}}
+}
+
+namespace test11 {
+  template<typename T> const int var = var<T>;
+  int k = var<int>;
+
+  template<typename T> struct X {
+    static const int b = false;
+    static const int k = X<T>::b ? X<T>::k : 0;
+  };
+  template<typename T> const int X<T>::k;
+  int q = X<int>::k;
+
+  template<typename T> struct Y {
+    static const int k;
+  };
+  // OK (but not constant initialization).
+  template<typename T> const int Y<T>::k = Y<T>::k;
+  int r = Y<int>::k;
+}
+
+namespace test12 {
+  template<typename T> int f(T t, int = f(T())) {} // expected-error {{recursive evaluation of default argument}} expected-note {{instantiation of}}
+  struct X {};
+  int q = f(X()); // expected-note {{instantiation of}}
+}
+
+namespace test13 {
+  struct A {
+    // Cycle via type of non-type template parameter.
+    template<typename T, typename T::template W<T>::type U = 0> struct W { using type = int; };
+    // Cycle via default template argument.
+    template<typename T, typename U = typename T::template X<T>> struct X {};
+    template<typename T, int U = T::template Y<T>::value> struct Y { static const int value = 0; };
+    template<typename T, template<typename> typename U = T::template Z<T>::template nested> struct Z { template<typename> struct nested; };
+  };
+  template<typename T> struct Wrap {
+    template<typename U> struct W : A::W<T> {};
+    template<typename U> struct X : A::X<T> {};
+    template<typename U> struct Y : A::Y<T> {};
+    template<typename U> struct Z : A::Z<T> {};
+  };
+  struct B {
+    template<typename U> struct W { using type = int; };
+    template<typename U> struct X {};
+    template<typename U> struct Y { static const int value = 0; };
+    template<typename U> struct Z { template<typename> struct nested; };
+  };
+
+  A::W<B> awb;
+  A::X<B> axb;
+  A::Y<B> ayb;
+  A::Z<B> azb;
+
+  A::W<Wrap<Wrap<B>>> awwwb;
+  A::X<Wrap<Wrap<B>>> axwwb;
+  A::Y<Wrap<Wrap<B>>> aywwb;
+  A::Z<Wrap<Wrap<B>>> azwwb;
+
+  // FIXME: These tests cause us to use too much stack and crash on a self-hosted debug build.
+  // FIXME: Check for recursion here and give a better diagnostic.
+#if 0
+  A::W<A> awa;
+  A::X<A> axa;
+  A::Y<A> aya;
+  A::Z<A> aza;
+#endif
+}