--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaTemplate/instantiate-requires-expr.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,216 @@
+// RUN: %clang_cc1 -std=c++2a -x c++ %s -verify -Wno-unused-value
+
+template<typename T, typename U>
+constexpr bool is_same_v = false;
+
+template<typename T>
+constexpr bool is_same_v<T, T> = true;
+
+// We use a hack in this file to make the compiler print out the requires
+// expression after it has been instantiated - we put false_v<requires {...}> as
+// the requires clause of a class template, then instantiate the template.
+// The requirement will not be satisfied, and the explaining diagnostic will
+// print out false_v<requires {...}> in its raw form (the false_v serves to
+// prevent the diagnostic from elaborating on why the requires expr wasn't
+// satisfied).
+
+template<bool v>
+constexpr bool false_v = false;
+
+template<typename... Ts>
+using void_t = void;
+
+// Check that requires parameters are instantiated correctly.
+
+template<typename T> requires
+false_v<requires (T t) { requires is_same_v<decltype(t), int>; }>
+// expected-note@-1 {{because 'false_v<requires (int t) { requires is_same_v<decltype(t), int>; }>' evaluated to false}}
+// expected-note@-2 {{because 'false_v<requires (char t) { requires is_same_v<decltype(t), int>; }>' evaluated to false}}
+struct r1 {};
+
+using r1i1 = r1<int>; // expected-error {{constraints not satisfied for class template 'r1' [with T = int]}}
+using r1i2 = r1<char>; // expected-error {{constraints not satisfied for class template 'r1' [with T = char]}}
+
+// Check that parameter packs work.
+
+template<typename... Ts> requires
+false_v<requires (Ts... ts) {requires ((sizeof(ts) == 2) && ...);}>
+// expected-note@-1 {{because 'false_v<requires (short ts, unsigned short ts) { requires (sizeof (ts) == 2) && (sizeof (ts) == 2); }>'}}
+// expected-note@-2 {{because 'false_v<requires (short ts) { requires (sizeof (ts) == 2); }>' evaluated to false}}
+struct r2 {};
+
+using r2i1 = r2<short, unsigned short>; // expected-error {{constraints not satisfied for class template 'r2' [with Ts = <short, unsigned short>]}}
+using r2i2 = r2<short>; // expected-error {{constraints not satisfied for class template 'r2' [with Ts = <short>]}}
+
+template<typename... Ts> requires
+false_v<(requires (Ts ts) {requires sizeof(ts) != 0;} && ...)>
+// expected-note@-1 {{because 'false_v<requires (short ts) { requires sizeof (ts) != 0; } && requires (unsigned short ts) { requires sizeof (ts) != 0; }>' evaluated to false}}
+// expected-note@-2 {{because 'false_v<requires (short ts) { requires sizeof (ts) != 0; }>' evaluated to false}}
+struct r3 {};
+
+using r3i1 = r3<short, unsigned short>; // expected-error {{constraints not satisfied for class template 'r3' [with Ts = <short, unsigned short>]}}
+using r3i2 = r3<short>; // expected-error {{constraints not satisfied for class template 'r3' [with Ts = <short>]}}
+
+template<typename T>
+struct identity { using type = T; };
+
+namespace type_requirement {
+  struct A {};
+
+  // check that nested name specifier is instantiated correctly.
+  template<typename T> requires false_v<requires { typename T::type; }> // expected-note{{because 'false_v<requires { typename identity<int>::type; }>' evaluated to false}}
+  struct r1 {};
+
+  using r1i = r1<identity<int>>; // expected-error{{constraints not satisfied for class template 'r1' [with T = identity<int>]}}
+
+  // check that template argument list is instantiated correctly.
+  template<typename T>
+  struct contains_template {
+      template<typename U> requires is_same_v<contains_template<T>, U>
+      using temp = int;
+  };
+
+  template<typename T> requires
+  false_v<requires { typename T::template temp<T>; }>
+  // expected-note@-1 {{because 'false_v<requires { typename contains_template<int>::temp<contains_template<int> >; }>' evaluated to false}}
+  // expected-note@-2 {{because 'false_v<requires { typename contains_template<short>::temp<contains_template<short> >; }>' evaluated to false}}
+  struct r2 {};
+
+  using r2i1 = r2<contains_template<int>>; // expected-error{{constraints not satisfied for class template 'r2' [with T = type_requirement::contains_template<int>]}}
+  using r2i2 = r2<contains_template<short>>; // expected-error{{constraints not satisfied for class template 'r2' [with T = type_requirement::contains_template<short>]}}
+
+  // substitution error occurs, then requires expr is instantiated again
+
+  template<typename T>
+  struct a {
+      template<typename U> requires (requires { typename T::a::a; }, false)
+      // expected-note@-1{{because 'requires { <<error-type>>; } , false' evaluated to false}}
+      struct r {};
+  };
+
+  using ari = a<int>::r<short>; // expected-error{{constraints not satisfied for class template 'r' [with U = short]}}
+
+  // Parameter pack inside expr
+  template<typename... Ts> requires
+  false_v<(requires { typename Ts::type; } && ...)>
+  // expected-note@-1 {{because 'false_v<requires { typename identity<short>::type; } && requires { typename identity<int>::type; } && requires { <<error-type>>; }>' evaluated to false}}
+  struct r5 {};
+
+  using r5i = r5<identity<short>, identity<int>, short>; // expected-error{{constraints not satisfied for class template 'r5' [with Ts = <identity<short>, identity<int>, short>]}}
+  template<typename... Ts> requires
+  false_v<(requires { typename void_t<Ts>; } && ...)> // expected-note{{because 'false_v<requires { typename void_t<int>; } && requires { typename void_t<short>; }>' evaluated to false}}
+  struct r6 {};
+
+  using r6i = r6<int, short>; // expected-error{{constraints not satisfied for class template 'r6' [with Ts = <int, short>]}}
+
+  template<typename... Ts> requires
+  false_v<(requires { typename Ts::template aaa<Ts>; } && ...)>
+  // expected-note@-1 {{because 'false_v<requires { <<error-type>>; } && requires { <<error-type>>; }>' evaluated to false}}
+  struct r7 {};
+
+  using r7i = r7<int, A>; // expected-error{{constraints not satisfied for class template 'r7' [with Ts = <int, type_requirement::A>]}}
+}
+
+namespace expr_requirement {
+  // check that compound/simple requirements are instantiated correctly.
+
+  template<typename T> requires false_v<requires { sizeof(T); { sizeof(T) }; }>
+  // expected-note@-1 {{because 'false_v<requires { sizeof(int); { sizeof(int) }; }>' evaluated to false}}
+  // expected-note@-2 {{because 'false_v<requires { <<error-expression>>; { sizeof(T) }; }>' evaluated to false}}
+  struct r1 {};
+
+  using r1i1 = r1<int>; // expected-error{{constraints not satisfied for class template 'r1' [with T = int]}}
+  using r1i2 = r1<void>; // expected-error{{constraints not satisfied for class template 'r1' [with T = void]}}
+
+  // substitution error occurs in expr, then expr is instantiated again.
+
+  template<typename T>
+  struct a {
+      template<typename U> requires (requires { sizeof(T::a); }, false) // expected-note{{because 'requires { <<error-expression>>; } , false' evaluated to false}}
+      struct r {};
+  };
+
+  using ari = a<int>::r<short>; // expected-error{{constraints not satisfied for class template 'r' [with U = short]}}
+
+  // check that the return-type-requirement is instantiated correctly.
+
+  template<typename T, typename U = int>
+  concept C1 = is_same_v<T, U>;
+
+  template<typename T> requires false_v<requires(T t) { { t } -> C1<T>; }>
+  // expected-note@-1 {{because 'false_v<requires (int t) { { t } -> C1<int>; }>' evaluated to false}}
+  // expected-note@-2 {{because 'false_v<requires (double t) { { t } -> C1<double>; }>' evaluated to false}}
+  struct r2 {};
+
+  using r2i1 = r2<int>; // expected-error{{constraints not satisfied for class template 'r2' [with T = int]}}
+  using r2i2 = r2<double>; // expected-error{{constraints not satisfied for class template 'r2' [with T = double]}}
+
+
+  // substitution error occurs in return type requirement, then requires expr is
+  // instantiated again.
+
+  template<typename T>
+  struct b {
+      template<typename U> requires (requires { { 0 } -> C1<typename T::a>; }, false) // expected-note{{because 'requires { { 0 } -> <<error-type>>; } , false' evaluated to false}}
+      struct r {};
+  };
+
+  using bri = b<int>::r<short>; // expected-error{{constraints not satisfied for class template 'r' [with U = short]}}
+
+
+  template<typename... Ts> requires
+  false_v<(requires { { 0 } noexcept -> C1<Ts>; } && ...)>
+  // expected-note@-1 {{because 'false_v<requires { { 0 } noexcept -> C1<int>; } && requires { { 0 } noexcept -> C1<unsigned int>; }>' evaluated to false}}
+  struct r3 {};
+
+  using r3i = r3<int, unsigned int>; // expected-error{{constraints not satisfied for class template 'r3' [with Ts = <int, unsigned int>]}}
+}
+
+namespace nested_requirement {
+  // check that constraint expression is instantiated correctly
+  template<typename T> requires false_v<requires { requires sizeof(T) == 2; }> // expected-note{{because 'false_v<requires { requires sizeof(int) == 2; }>' evaluated to false}}
+  struct r1 {};
+
+  using r1i = r1<int>; // expected-error{{constraints not satisfied for class template 'r1' [with T = int]}}
+
+  // substitution error occurs in expr, then expr is instantiated again.
+  template<typename T>
+  struct a {
+      template<typename U> requires
+      (requires { requires sizeof(T::a) == 0; }, false) // expected-note{{because 'requires { requires <<error-expression>>; } , false' evaluated to false}}
+      struct r {};
+  };
+
+  using ari = a<int>::r<short>; // expected-error{{constraints not satisfied for class template 'r' [with U = short]}}
+
+  // Parameter pack inside expr
+  template<typename... Ts> requires
+  false_v<(requires { requires sizeof(Ts) == 0; } && ...)>
+  // expected-note@-1 {{because 'false_v<requires { requires sizeof(int) == 0; } && requires { requires sizeof(short) == 0; }>' evaluated to false}}
+  struct r2 {};
+
+  using r2i = r2<int, short>; // expected-error{{constraints not satisfied for class template 'r2' [with Ts = <int, short>]}}
+}
+
+// Parameter pack inside multiple requirements
+template<typename... Ts> requires
+false_v<(requires { requires sizeof(Ts) == 0; sizeof(Ts); } && ...)>
+// expected-note@-1 {{because 'false_v<requires { requires sizeof(int) == 0; sizeof(Ts); } && requires { requires sizeof(short) == 0; sizeof(Ts); }>' evaluated to false}}
+struct r4 {};
+
+using r4i = r4<int, short>; // expected-error{{constraints not satisfied for class template 'r4' [with Ts = <int, short>]}}
+
+template<typename... Ts> requires
+false_v<(requires(Ts t) { requires sizeof(t) == 0; t++; } && ...)>
+// expected-note@-1 {{because 'false_v<requires (int t) { requires sizeof (t) == 0; t++; } && requires (short t) { requires sizeof (t) == 0; t++; }>' evaluated to false}}
+struct r5 {};
+
+using r5i = r5<int, short>; // expected-error{{constraints not satisfied for class template 'r5' [with Ts = <int, short>]}}
+
+template<typename T> requires
+false_v<(requires(T t) { T{t}; })> // T{t} creates an "UnevaluatedList" context.
+// expected-note@-1 {{because 'false_v<(requires (int t) { int{t}; })>' evaluated to false}}
+struct r6 {};
+
+using r6i = r6<int>;
+// expected-error@-1 {{constraints not satisfied for class template 'r6' [with T = int]}}