diff --git a/clang-tools-extra/test/clang-tidy/checkers/Inputs/readability-identifier-naming/system/coroutines.h b/clang-tools-extra/test/clang-tidy/checkers/Inputs/readability-identifier-naming/system/coroutines.h
--- a/clang-tools-extra/test/clang-tidy/checkers/Inputs/readability-identifier-naming/system/coroutines.h
+++ b/clang-tools-extra/test/clang-tidy/checkers/Inputs/readability-identifier-naming/system/coroutines.h
@@ -1,6 +1,7 @@
 #pragma once
 
 namespace std {
+namespace experimental {
 
 template <typename ret_t, typename... args_t>
 struct coroutine_traits {
@@ -12,6 +13,7 @@
   static constexpr coroutine_handle from_address(void *addr) noexcept { return {}; };
 };
 
+} // namespace experimental
 } // namespace std
 
 struct never_suspend {
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -2872,7 +2872,7 @@
 
 Clang provides experimental builtins to support C++ Coroutines as defined by
 https://wg21.link/P0057. The following four are intended to be used by the
-standard library to implement `std::coroutine_handle` type.
+standard library to implement `std::experimental::coroutine_handle` type.
 
 **Syntax**:
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10957,20 +10957,19 @@
   "|a function with a deduced return type|a varargs function"
   "|a consteval function}0">;
 def err_implied_coroutine_type_not_found : Error<
-  "%0 type was not found; include <coroutine> before defining "
-  "a coroutine; include <experimental/coroutine> if your version "
-  "of libcxx is less than 14.0">;
+  "%0 type was not found; include <experimental/coroutine> before defining "
+  "a coroutine">;
 def err_implicit_coroutine_std_nothrow_type_not_found : Error<
   "std::nothrow was not found; include <new> before defining a coroutine which "
   "uses get_return_object_on_allocation_failure()">;
 def err_malformed_std_nothrow : Error<
   "std::nothrow must be a valid variable declaration">;
 def err_malformed_std_coroutine_handle : Error<
-  "std::coroutine_handle must be a class template">;
+  "std::experimental::coroutine_handle must be a class template">;
 def err_coroutine_handle_missing_member : Error<
-  "std::coroutine_handle missing a member named '%0'">;
+  "std::experimental::coroutine_handle missing a member named '%0'">;
 def err_malformed_std_coroutine_traits : Error<
-  "'std::coroutine_traits' must be a class template">;
+  "'std::experimental::coroutine_traits' must be a class template">;
 def err_implied_std_coroutine_traits_promise_type_not_found : Error<
   "this function cannot be a coroutine: %q0 has no member named 'promise_type'">;
 def err_implied_std_coroutine_traits_promise_type_not_class : Error<
@@ -11012,10 +11011,6 @@
 def warn_coroutine_handle_address_invalid_return_type : Warning <
   "return type of 'coroutine_handle<>::address should be 'void*' (have %0) in order to get capability with existing async C API.">,
   InGroup<Coroutine>;
-def warn_coroutine_in_legacy_experimental_space : Warning <
-  "coroutine_traits defined in std::experimental namespace is deprecated. "
-  "Consider updating libcxx and include <coroutine> instead of <experimental/coroutine>.">,
-  InGroup<Coroutine>;
 def err_coroutine_promise_final_suspend_requires_nothrow : Error<
   "the expression 'co_await __promise.final_suspend()' is required to be non-throwing"
 >;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1128,10 +1128,6 @@
   /// The C++ "std::coroutine_traits" template, which is defined in
   /// \<coroutine_traits>
   ClassTemplateDecl *StdCoroutineTraitsCache;
-  /// The namespace where coroutine components are defined. In standard,
-  /// they are defined in std namespace. And in the previous implementation,
-  /// they are defined in std::experimental namespace.
-  NamespaceDecl *CoroTraitsNamespaceCache;
 
   /// The C++ "type_info" declaration, which is defined in \<typeinfo>.
   RecordDecl *CXXTypeInfoDecl;
@@ -5666,7 +5662,6 @@
   NamespaceDecl *getOrCreateStdNamespace();
 
   NamespaceDecl *lookupStdExperimentalNamespace();
-  NamespaceDecl *getCachedCoroNamespace() { return CoroTraitsNamespaceCache; }
 
   CXXRecordDecl *getStdBadAlloc() const;
   EnumDecl *getStdAlignValT() const;
@@ -10223,11 +10218,8 @@
   bool buildCoroutineParameterMoves(SourceLocation Loc);
   VarDecl *buildCoroutinePromise(SourceLocation Loc);
   void CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body);
-  /// Lookup 'coroutine_traits' in std namespace and std::experimental
-  /// namespace. The namespace found would be recorded in Namespace.
   ClassTemplateDecl *lookupCoroutineTraits(SourceLocation KwLoc,
-                                           SourceLocation FuncLoc,
-                                           NamespaceDecl *&Namespace);
+                                           SourceLocation FuncLoc);
   /// Check that the expression co_await promise.final_suspend() shall not be
   /// potentially-throwing.
   bool checkFinalSuspendNoThrow(const Stmt *FinalSuspend);
diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -53,10 +53,15 @@
                                   SourceLocation KwLoc) {
   const FunctionProtoType *FnType = FD->getType()->castAs<FunctionProtoType>();
   const SourceLocation FuncLoc = FD->getLocation();
+  // FIXME: Cache std::coroutine_traits once we've found it.
+  NamespaceDecl *StdExp = S.lookupStdExperimentalNamespace();
+  if (!StdExp) {
+    S.Diag(KwLoc, diag::err_implied_coroutine_type_not_found)
+        << "std::experimental::coroutine_traits";
+    return QualType();
+  }
 
-  NamespaceDecl *CoroNamespace = nullptr;
-  ClassTemplateDecl *CoroTraits =
-      S.lookupCoroutineTraits(KwLoc, FuncLoc, CoroNamespace);
+  ClassTemplateDecl *CoroTraits = S.lookupCoroutineTraits(KwLoc, FuncLoc);
   if (!CoroTraits) {
     return QualType();
   }
@@ -117,7 +122,7 @@
   QualType PromiseType = S.Context.getTypeDeclType(Promise);
 
   auto buildElaboratedType = [&]() {
-    auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, CoroNamespace);
+    auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, StdExp);
     NNS = NestedNameSpecifier::Create(S.Context, NNS, false,
                                       CoroTrait.getTypePtr());
     return S.Context.getElaboratedType(ETK_None, NNS, PromiseType);
@@ -136,20 +141,20 @@
   return PromiseType;
 }
 
-/// Look up the std::coroutine_handle<PromiseType>.
+/// Look up the std::experimental::coroutine_handle<PromiseType>.
 static QualType lookupCoroutineHandleType(Sema &S, QualType PromiseType,
                                           SourceLocation Loc) {
   if (PromiseType.isNull())
     return QualType();
 
-  NamespaceDecl *CoroNamespace = S.getCachedCoroNamespace();
-  assert(CoroNamespace && "Should already be diagnosed");
+  NamespaceDecl *StdExp = S.lookupStdExperimentalNamespace();
+  assert(StdExp && "Should already be diagnosed");
 
   LookupResult Result(S, &S.PP.getIdentifierTable().get("coroutine_handle"),
                       Loc, Sema::LookupOrdinaryName);
-  if (!S.LookupQualifiedName(Result, CoroNamespace)) {
+  if (!S.LookupQualifiedName(Result, StdExp)) {
     S.Diag(Loc, diag::err_implied_coroutine_type_not_found)
-        << "std::coroutine_handle";
+        << "std::experimental::coroutine_handle";
     return QualType();
   }
 
@@ -995,7 +1000,7 @@
   LookupResult Result(S, &S.PP.getIdentifierTable().get("nothrow"), Loc,
                       Sema::LookupOrdinaryName);
   if (!S.LookupQualifiedName(Result, Std)) {
-    // FIXME: <coroutine> should have been included already.
+    // FIXME: <experimental/coroutine> should have been included already.
     // If we require it to include <new> then this diagnostic is no longer
     // needed.
     S.Diag(Loc, diag::err_implicit_coroutine_std_nothrow_type_not_found);
@@ -1658,32 +1663,25 @@
 }
 
 ClassTemplateDecl *Sema::lookupCoroutineTraits(SourceLocation KwLoc,
-                                               SourceLocation FuncLoc,
-                                               NamespaceDecl *&Namespace) {
+                                               SourceLocation FuncLoc) {
   if (!StdCoroutineTraitsCache) {
-    NamespaceDecl *CoroNamespace = getStdNamespace();
-    LookupResult Result(*this, &PP.getIdentifierTable().get("coroutine_traits"),
-                        FuncLoc, LookupOrdinaryName);
-    if (!CoroNamespace || !LookupQualifiedName(Result, CoroNamespace)) {
-      /// TODO: lookup in std::expeirmental namespace for compability.
-      /// Remove this once users get familiar with coroutine under std
-      /// namespace.
-      CoroNamespace = lookupStdExperimentalNamespace();
-      if (!CoroNamespace || !LookupQualifiedName(Result, CoroNamespace)) {
+    if (auto StdExp = lookupStdExperimentalNamespace()) {
+      LookupResult Result(*this,
+                          &PP.getIdentifierTable().get("coroutine_traits"),
+                          FuncLoc, LookupOrdinaryName);
+      if (!LookupQualifiedName(Result, StdExp)) {
         Diag(KwLoc, diag::err_implied_coroutine_type_not_found)
-            << "std::coroutine_traits";
+            << "std::experimental::coroutine_traits";
+        return nullptr;
+      }
+      if (!(StdCoroutineTraitsCache =
+                Result.getAsSingle<ClassTemplateDecl>())) {
+        Result.suppressDiagnostics();
+        NamedDecl *Found = *Result.begin();
+        Diag(Found->getLocation(), diag::err_malformed_std_coroutine_traits);
         return nullptr;
       }
-      Diag(KwLoc, diag::warn_coroutine_in_legacy_experimental_space);
-    }
-    if (!(StdCoroutineTraitsCache = Result.getAsSingle<ClassTemplateDecl>())) {
-      Result.suppressDiagnostics();
-      NamedDecl *Found = *Result.begin();
-      Diag(Found->getLocation(), diag::err_malformed_std_coroutine_traits);
-      return nullptr;
     }
-    CoroTraitsNamespaceCache = CoroNamespace;
   }
-  Namespace = CoroTraitsNamespaceCache;
   return StdCoroutineTraitsCache;
 }
diff --git a/clang/test/AST/Inputs/std-coroutine.h b/clang/test/AST/Inputs/std-coroutine.h
--- a/clang/test/AST/Inputs/std-coroutine.h
+++ b/clang/test/AST/Inputs/std-coroutine.h
@@ -3,6 +3,7 @@
 #define STD_COROUTINE_H
 
 namespace std {
+namespace experimental {
 
 template <typename R, typename...> struct coroutine_traits {
   using promise_type = typename R::promise_type;
@@ -66,6 +67,7 @@
   void await_resume() noexcept {}
 };
 
+} // namespace experimental
 } // namespace std
 
 #endif // STD_COROUTINE_H
diff --git a/clang/test/AST/coroutine-locals-cleanup.cpp b/clang/test/AST/coroutine-locals-cleanup.cpp
--- a/clang/test/AST/coroutine-locals-cleanup.cpp
+++ b/clang/test/AST/coroutine-locals-cleanup.cpp
@@ -2,7 +2,7 @@
 
 #include "Inputs/std-coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
 
 struct Task {
   struct promise_type {
diff --git a/clang/test/AST/coroutine-source-location-crash.cpp b/clang/test/AST/coroutine-source-location-crash.cpp
--- a/clang/test/AST/coroutine-source-location-crash.cpp
+++ b/clang/test/AST/coroutine-source-location-crash.cpp
@@ -11,7 +11,7 @@
 
 #include "Inputs/std-coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
 
 struct A {
   bool await_ready();
diff --git a/clang/test/Analysis/more-dtors-cfg-output.cpp b/clang/test/Analysis/more-dtors-cfg-output.cpp
--- a/clang/test/Analysis/more-dtors-cfg-output.cpp
+++ b/clang/test/Analysis/more-dtors-cfg-output.cpp
@@ -275,32 +275,32 @@
 #if CXX2A
 // Boilerplate needed to test co_return:
 
-namespace std {
-template <typename Promise>
-struct coroutine_handle {
-  static coroutine_handle from_address(void *) noexcept;
-};
-} // namespace std
+namespace std::experimental {
+  template <typename Promise>
+  struct coroutine_handle {
+    static coroutine_handle from_address(void *) noexcept;
+  };
+}
 
 struct TestPromise {
   TestPromise initial_suspend();
   TestPromise final_suspend() noexcept;
   bool await_ready() noexcept;
-  void await_suspend(const std::coroutine_handle<TestPromise> &) noexcept;
+  void await_suspend(const std::experimental::coroutine_handle<TestPromise> &) noexcept;
   void await_resume() noexcept;
   Foo return_value(const Bar &);
   Bar get_return_object();
   void unhandled_exception();
 };
 
-namespace std {
-template <typename Ret, typename... Args>
-struct coroutine_traits;
-template <>
-struct coroutine_traits<Bar> {
-  using promise_type = TestPromise;
-};
-} // namespace std
+namespace std::experimental {
+  template <typename Ret, typename... Args>
+  struct coroutine_traits;
+  template <>
+  struct coroutine_traits<Bar> {
+      using promise_type = TestPromise;
+  };
+}
 
 Bar coreturn() {
   co_return get_bar();
diff --git a/clang/test/CodeGenCXX/ubsan-coroutines.cpp b/clang/test/CodeGenCXX/ubsan-coroutines.cpp
--- a/clang/test/CodeGenCXX/ubsan-coroutines.cpp
+++ b/clang/test/CodeGenCXX/ubsan-coroutines.cpp
@@ -4,7 +4,7 @@
 // llvm.coro.* intrinsics have not yet been ported.
 // RUN: %clang_cc1 -fno-experimental-new-pass-manager -emit-obj -std=c++2a -fsanitize=null %s -o %t.o
 
-namespace std {
+namespace std::experimental {
 template <typename R, typename... T> struct coroutine_traits {
   using promise_type = typename R::promise_type;
 };
@@ -20,11 +20,11 @@
   coroutine_handle() = default;
   static coroutine_handle from_address(void *) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
@@ -41,7 +41,7 @@
 struct awaitable {
   task await() { (void)co_await *this; }
   bool await_ready() { return false; }
-  bool await_suspend(std::coroutine_handle<> awaiter) { return false; }
+  bool await_suspend(std::experimental::coroutine_handle<> awaiter) { return false; }
   bool await_resume() { return false; }
 };
 
diff --git a/clang/test/CodeGenCoroutines/Inputs/coroutine.h b/clang/test/CodeGenCoroutines/Inputs/coroutine.h
--- a/clang/test/CodeGenCoroutines/Inputs/coroutine.h
+++ b/clang/test/CodeGenCoroutines/Inputs/coroutine.h
@@ -1,6 +1,6 @@
 #pragma once
 
-namespace std {
+namespace std { namespace experimental { inline namespace coroutines_v1 {
 
 template <typename R, typename...> struct coroutine_traits {
   using promise_type = typename R::promise_type;
@@ -77,4 +77,4 @@
   void await_resume() noexcept {}
 };
 
-} // namespace std
+}}}
diff --git a/clang/test/CodeGenCoroutines/coro-alloc.cpp b/clang/test/CodeGenCoroutines/coro-alloc.cpp
--- a/clang/test/CodeGenCoroutines/coro-alloc.cpp
+++ b/clang/test/CodeGenCoroutines/coro-alloc.cpp
@@ -3,6 +3,7 @@
 // RUN:   | FileCheck %s
 
 namespace std {
+namespace experimental {
 template <typename... T>
 struct coroutine_traits; // expected-note {{declared here}}
 
@@ -20,6 +21,8 @@
   coroutine_handle(coroutine_handle<PromiseType>) noexcept {}
 };
 
+} // end namespace experimental
+
 struct nothrow_t {};
 constexpr nothrow_t nothrow = {};
 
@@ -34,14 +37,14 @@
 
 struct suspend_always {
   bool await_ready() noexcept { return false; }
-  void await_suspend(std::coroutine_handle<>) noexcept {}
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept {}
   void await_resume() noexcept {}
 };
 
 struct global_new_delete_tag {};
 
-template <>
-struct std::coroutine_traits<void, global_new_delete_tag> {
+template<>
+struct std::experimental::coroutine_traits<void, global_new_delete_tag> {
   struct promise_type {
     void get_return_object() {}
     suspend_always initial_suspend() { return {}; }
@@ -80,8 +83,8 @@
 
 struct promise_new_tag {};
 
-template <>
-struct std::coroutine_traits<void, promise_new_tag> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_new_tag> {
   struct promise_type {
     void *operator new(unsigned long);
     void get_return_object() {}
@@ -95,7 +98,7 @@
 extern "C" void f1(promise_new_tag ) {
   // CHECK: %[[ID:.+]] = call token @llvm.coro.id(i32 16
   // CHECK: %[[SIZE:.+]] = call i64 @llvm.coro.size.i64()
-  // CHECK: call i8* @_ZNSt16coroutine_traitsIJv15promise_new_tagEE12promise_typenwEm(i64 %[[SIZE]])
+  // CHECK: call i8* @_ZNSt12experimental16coroutine_traitsIJv15promise_new_tagEE12promise_typenwEm(i64 %[[SIZE]])
 
   // CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.begin(
   // CHECK: %[[MEM:.+]] = call i8* @llvm.coro.free(token %[[ID]], i8* %[[FRAME]])
@@ -105,8 +108,8 @@
 
 struct promise_matching_placement_new_tag {};
 
-template <>
-struct std::coroutine_traits<void, promise_matching_placement_new_tag, int, float, double> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_matching_placement_new_tag, int, float, double> {
   struct promise_type {
     void *operator new(unsigned long, promise_matching_placement_new_tag,
                        int, float, double);
@@ -127,7 +130,7 @@
   // CHECK: %[[INT:.+]] = load i32, i32* %x.addr, align 4
   // CHECK: %[[FLOAT:.+]] = load float, float* %y.addr, align 4
   // CHECK: %[[DOUBLE:.+]] = load double, double* %z.addr, align 8
-  // CHECK: call i8* @_ZNSt16coroutine_traitsIJv34promise_matching_placement_new_tagifdEE12promise_typenwEmS0_ifd(i64 %[[SIZE]], i32 %[[INT]], float %[[FLOAT]], double %[[DOUBLE]])
+  // CHECK: call i8* @_ZNSt12experimental16coroutine_traitsIJv34promise_matching_placement_new_tagifdEE12promise_typenwEmS1_ifd(i64 %[[SIZE]], i32 %[[INT]], float %[[FLOAT]], double %[[DOUBLE]])
   co_return;
 }
 
@@ -137,8 +140,8 @@
 
 struct promise_matching_global_placement_new_tag {};
 struct dummy {};
-template <>
-struct std::coroutine_traits<void, promise_matching_global_placement_new_tag, dummy *> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_matching_global_placement_new_tag, dummy*> {
   struct promise_type {
     void get_return_object() {}
     suspend_always initial_suspend() { return {}; }
@@ -159,8 +162,8 @@
 
 struct promise_delete_tag {};
 
-template <>
-struct std::coroutine_traits<void, promise_delete_tag> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_delete_tag> {
   struct promise_type {
     void operator delete(void*);
     void get_return_object() {}
@@ -178,14 +181,14 @@
 
   // CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.begin(
   // CHECK: %[[MEM:.+]] = call i8* @llvm.coro.free(token %[[ID]], i8* %[[FRAME]])
-  // CHECK: call void @_ZNSt16coroutine_traitsIJv18promise_delete_tagEE12promise_typedlEPv(i8* %[[MEM]])
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJv18promise_delete_tagEE12promise_typedlEPv(i8* %[[MEM]])
   co_return;
 }
 
 struct promise_sized_delete_tag {};
 
-template <>
-struct std::coroutine_traits<void, promise_sized_delete_tag> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_sized_delete_tag> {
   struct promise_type {
     void operator delete(void*, unsigned long);
     void get_return_object() {}
@@ -204,14 +207,14 @@
   // CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.begin(
   // CHECK: %[[MEM:.+]] = call i8* @llvm.coro.free(token %[[ID]], i8* %[[FRAME]])
   // CHECK: %[[SIZE2:.+]] = call i64 @llvm.coro.size.i64()
-  // CHECK: call void @_ZNSt16coroutine_traitsIJv24promise_sized_delete_tagEE12promise_typedlEPvm(i8* %[[MEM]], i64 %[[SIZE2]])
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJv24promise_sized_delete_tagEE12promise_typedlEPvm(i8* %[[MEM]], i64 %[[SIZE2]])
   co_return;
 }
 
 struct promise_on_alloc_failure_tag {};
 
-template <>
-struct std::coroutine_traits<int, promise_on_alloc_failure_tag> {
+template<>
+struct std::experimental::coroutine_traits<int, promise_on_alloc_failure_tag> {
   struct promise_type {
     int get_return_object() { return 0; }
     suspend_always initial_suspend() { return {}; }
@@ -232,12 +235,12 @@
   // CHECK: br i1 %[[OK]], label %[[OKBB:.+]], label %[[ERRBB:.+]]
 
   // CHECK: [[ERRBB]]:
-  // CHECK:   %[[FailRet:.+]] = call i32 @_ZNSt16coroutine_traitsIJi28promise_on_alloc_failure_tagEE12promise_type39get_return_object_on_allocation_failureEv(
+  // CHECK:   %[[FailRet:.+]] = call i32 @_ZNSt12experimental16coroutine_traitsIJi28promise_on_alloc_failure_tagEE12promise_type39get_return_object_on_allocation_failureEv(
   // CHECK:   store i32 %[[FailRet]], i32* %[[RetVal]]
   // CHECK:   br label %[[RetBB:.+]]
 
   // CHECK: [[OKBB]]:
-  // CHECK:   %[[OkRet:.+]] = call i32 @_ZNSt16coroutine_traitsIJi28promise_on_alloc_failure_tagEE12promise_type17get_return_objectEv(
+  // CHECK:   %[[OkRet:.+]] = call i32 @_ZNSt12experimental16coroutine_traitsIJi28promise_on_alloc_failure_tagEE12promise_type17get_return_objectEv(
   // CHECK:   store i32 %[[OkRet]], i32* %[[Gro]]
 
   // CHECK: %[[Tmp1:.*]] = load i32, i32* %[[Gro]]
diff --git a/clang/test/CodeGenCoroutines/coro-always-inline.cpp b/clang/test/CodeGenCoroutines/coro-always-inline.cpp
--- a/clang/test/CodeGenCoroutines/coro-always-inline.cpp
+++ b/clang/test/CodeGenCoroutines/coro-always-inline.cpp
@@ -9,6 +9,7 @@
 // RUN:   -fno-inline -O0 %s -o - | FileCheck %s
 
 namespace std {
+namespace experimental {
 
 struct handle {};
 
@@ -34,17 +35,18 @@
     void unhandled_exception() {}
   };
 };
+} // namespace experimental
 } // namespace std
 
 // CHECK-LABEL: @_Z3foov
 // CHECK-LABEL: entry:
-// CHECK: [[CAST0:%[0-9]+]] = bitcast %"struct.std::awaitable"* %ref.tmp{{.*}} to i8*
+// CHECK: [[CAST0:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"* %ref.tmp{{.*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 1, i8* [[CAST0]])
-// CHECK: [[CAST1:%[0-9]+]] = bitcast %"struct.std::awaitable"* %ref.tmp{{.*}} to i8*
+// CHECK: [[CAST1:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"* %ref.tmp{{.*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 1, i8* [[CAST1]])
 
-// CHECK: [[CAST2:%[0-9]+]] = bitcast %"struct.std::awaitable"* %ref.tmp{{.*}} to i8*
+// CHECK: [[CAST2:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"* %ref.tmp{{.*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 1, i8* [[CAST2]])
-// CHECK: [[CAST3:%[0-9]+]] = bitcast %"struct.std::awaitable"* %ref.tmp{{.*}} to i8*
+// CHECK: [[CAST3:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"* %ref.tmp{{.*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 1, i8* [[CAST3]])
 void foo() { co_return; }
diff --git a/clang/test/CodeGenCoroutines/coro-await-domination.cpp b/clang/test/CodeGenCoroutines/coro-await-domination.cpp
--- a/clang/test/CodeGenCoroutines/coro-await-domination.cpp
+++ b/clang/test/CodeGenCoroutines/coro-await-domination.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++14 -emit-llvm %s -o - | FileCheck %s
 #include "Inputs/coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
 
 struct coro {
   struct promise_type {
diff --git a/clang/test/CodeGenCoroutines/coro-await-resume-eh.cpp b/clang/test/CodeGenCoroutines/coro-await-resume-eh.cpp
--- a/clang/test/CodeGenCoroutines/coro-await-resume-eh.cpp
+++ b/clang/test/CodeGenCoroutines/coro-await-resume-eh.cpp
@@ -10,9 +10,11 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 struct throwing_awaitable {
   bool await_ready() { return true; }
-  void await_suspend(std::coroutine_handle<>) {}
+  void await_suspend(coro::coroutine_handle<>) {}
   void await_resume() { throw 42; }
 };
 
@@ -20,7 +22,7 @@
   struct promise_type {
     auto get_return_object() { return throwing_task{}; }
     auto initial_suspend() { return throwing_awaitable{}; }
-    auto final_suspend() noexcept { return std::suspend_never{}; }
+    auto final_suspend() noexcept { return coro::suspend_never{}; }
     void return_void() {}
     void unhandled_exception() {}
   };
@@ -86,7 +88,7 @@
 
 struct noexcept_awaitable {
   bool await_ready() { return true; }
-  void await_suspend(std::coroutine_handle<>) {}
+  void await_suspend(coro::coroutine_handle<>) {}
   void await_resume() noexcept {}
 };
 
@@ -94,7 +96,7 @@
   struct promise_type {
     auto get_return_object() { return noexcept_task{}; }
     auto initial_suspend() { return noexcept_awaitable{}; }
-    auto final_suspend() noexcept { return std::suspend_never{}; }
+    auto final_suspend() noexcept { return coro::suspend_never{}; }
     void return_void() {}
     void unhandled_exception() {}
   };
diff --git a/clang/test/CodeGenCoroutines/coro-await.cpp b/clang/test/CodeGenCoroutines/coro-await.cpp
--- a/clang/test/CodeGenCoroutines/coro-await.cpp
+++ b/clang/test/CodeGenCoroutines/coro-await.cpp
@@ -2,6 +2,7 @@
 // RUN:   -emit-llvm %s -o - -disable-llvm-passes -Wno-coroutine -Wno-unused | FileCheck %s
 
 namespace std {
+namespace experimental {
 template <typename... T>
 struct coroutine_traits;
 
@@ -19,28 +20,29 @@
   static coroutine_handle from_address(void *) noexcept;
 };
 
+}
 }
 
 struct init_susp {
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 struct final_susp {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
 struct suspend_always {
   int stuff;
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 
-template <>
-struct std::coroutine_traits<void> {
+template<>
+struct std::experimental::coroutine_traits<void> {
   struct promise_type {
     void get_return_object();
     init_susp initial_suspend();
@@ -55,7 +57,7 @@
 
   // See if initial_suspend was issued:
   // ----------------------------------
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvEE12promise_type15initial_suspendEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type15initial_suspendEv(
   // CHECK-NEXT: call zeroext i1 @_ZN9init_susp11await_readyEv(%struct.init_susp*
   // CHECK: %[[INITSP_ID:.+]] = call token @llvm.coro.save(
   // CHECK: call i8 @llvm.coro.suspend(token %[[INITSP_ID]], i1 false)
@@ -73,10 +75,10 @@
   // ---------------------------
   // Build the coroutine handle and pass it to await_suspend
   // ---------------------------
-  // CHECK: call i8* @_ZNSt16coroutine_handleINSt16coroutine_traitsIJvEE12promise_typeEE12from_addressEPv(i8* %[[FRAME]])
+  // CHECK: call i8* @_ZNSt12experimental16coroutine_handleINS_16coroutine_traitsIJvEE12promise_typeEE12from_addressEPv(i8* %[[FRAME]])
   //   ... many lines of code to coerce coroutine_handle into an i8* scalar
   // CHECK: %[[CH:.+]] = load i8*, i8** %{{.+}}
-  // CHECK: call void @_ZN14suspend_always13await_suspendESt16coroutine_handleIvE(%struct.suspend_always* {{[^,]*}} %[[AWAITABLE]], i8* %[[CH]])
+  // CHECK: call void @_ZN14suspend_always13await_suspendENSt12experimental16coroutine_handleIvEE(%struct.suspend_always* {{[^,]*}} %[[AWAITABLE]], i8* %[[CH]])
   // -------------------------
   // Generate a suspend point:
   // -------------------------
@@ -97,7 +99,7 @@
 
   // See if final_suspend was issued:
   // ----------------------------------
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvEE12promise_type13final_suspendEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type13final_suspendEv(
   // CHECK-NEXT: call zeroext i1 @_ZN10final_susp11await_readyEv(%struct.final_susp*
   // CHECK: %[[FINALSP_ID:.+]] = call token @llvm.coro.save(
   // CHECK: call i8 @llvm.coro.suspend(token %[[FINALSP_ID]], i1 true)
@@ -107,12 +109,13 @@
   float stuff;
   ~suspend_maybe();
   bool await_ready();
-  bool await_suspend(std::coroutine_handle<>);
+  bool await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 
-template <>
-struct std::coroutine_traits<void, int> {
+
+template<>
+struct std::experimental::coroutine_traits<void,int> {
   struct promise_type {
     void get_return_object();
     init_susp initial_suspend();
@@ -124,10 +127,10 @@
 
 // CHECK-LABEL: f1(
 extern "C" void f1(int) {
-  // CHECK: %[[PROMISE:.+]] = alloca %"struct.std::coroutine_traits<void, int>::promise_type"
+  // CHECK: %[[PROMISE:.+]] = alloca %"struct.std::experimental::coroutine_traits<void, int>::promise_type"
   // CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.begin(
   co_yield 42;
-  // CHECK: call void @_ZNSt16coroutine_traitsIJviEE12promise_type11yield_valueEi(%struct.suspend_maybe* sret(%struct.suspend_maybe) align 4 %[[AWAITER:.+]], %"struct.std::coroutine_traits<void, int>::promise_type"* {{[^,]*}} %[[PROMISE]], i32 42)
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJviEE12promise_type11yield_valueEi(%struct.suspend_maybe* sret(%struct.suspend_maybe) align 4 %[[AWAITER:.+]], %"struct.std::experimental::coroutine_traits<void, int>::promise_type"* {{[^,]*}} %[[PROMISE]], i32 42)
 
   // See if we need to suspend:
   // --------------------------
@@ -141,10 +144,10 @@
   // ---------------------------
   // Build the coroutine handle and pass it to await_suspend
   // ---------------------------
-  // CHECK: call i8* @_ZNSt16coroutine_handleINSt16coroutine_traitsIJviEE12promise_typeEE12from_addressEPv(i8* %[[FRAME]])
+  // CHECK: call i8* @_ZNSt12experimental16coroutine_handleINS_16coroutine_traitsIJviEE12promise_typeEE12from_addressEPv(i8* %[[FRAME]])
   //   ... many lines of code to coerce coroutine_handle into an i8* scalar
   // CHECK: %[[CH:.+]] = load i8*, i8** %{{.+}}
-  // CHECK: %[[YES:.+]] = call zeroext i1 @_ZN13suspend_maybe13await_suspendESt16coroutine_handleIvE(%struct.suspend_maybe* {{[^,]*}} %[[AWAITABLE]], i8* %[[CH]])
+  // CHECK: %[[YES:.+]] = call zeroext i1 @_ZN13suspend_maybe13await_suspendENSt12experimental16coroutine_handleIvEE(%struct.suspend_maybe* {{[^,]*}} %[[AWAITABLE]], i8* %[[CH]])
   // -------------------------------------------
   // See if await_suspend decided not to suspend
   // -------------------------------------------
@@ -261,7 +264,7 @@
 
   // See if initial_suspend was issued:
   // ----------------------------------
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvEE12promise_type15initial_suspendEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type15initial_suspendEv(
   // CHECK-NEXT: call zeroext i1 @_ZN9init_susp11await_readyEv(%struct.init_susp*
 
   for (;;)
@@ -269,7 +272,7 @@
 
   // Verify that final_suspend was NOT issued:
   // ----------------------------------
-  // CHECK-NOT: call void @_ZNSt16coroutine_traitsIJvEE12promise_type13final_suspendEv(
+  // CHECK-NOT: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type13final_suspendEv(
   // CHECK-NOT: call zeroext i1 @_ZN10final_susp11await_readyEv(%struct.final_susp*
 }
 
@@ -284,12 +287,13 @@
 
 struct AwaitResumeReturnsLValue {
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
   RefTag& await_resume();
 };
 
-template <>
-struct std::coroutine_traits<void, double> {
+
+template<>
+struct std::experimental::coroutine_traits<void,double> {
   struct promise_type {
     void get_return_object();
     init_susp initial_suspend();
@@ -334,7 +338,7 @@
 
 struct TailCallAwait {
   bool await_ready();
-  std::coroutine_handle<> await_suspend(std::coroutine_handle<>);
+  std::experimental::coroutine_handle<> await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 
@@ -342,9 +346,9 @@
 extern "C" void TestTailcall() {
   co_await TailCallAwait{};
 
-  // CHECK: %[[RESULT:.+]] = call i8* @_ZN13TailCallAwait13await_suspendESt16coroutine_handleIvE(%struct.TailCallAwait*
-  // CHECK: %[[COERCE:.+]] = getelementptr inbounds %"struct.std::coroutine_handle", %"struct.std::coroutine_handle"* %[[TMP:.+]], i32 0, i32 0
+  // CHECK: %[[RESULT:.+]] = call i8* @_ZN13TailCallAwait13await_suspendENSt12experimental16coroutine_handleIvEE(%struct.TailCallAwait*
+  // CHECK: %[[COERCE:.+]] = getelementptr inbounds %"struct.std::experimental::coroutine_handle", %"struct.std::experimental::coroutine_handle"* %[[TMP:.+]], i32 0, i32 0
   // CHECK: store i8* %[[RESULT]], i8** %[[COERCE]]
-  // CHECK: %[[ADDR:.+]] = call i8* @_ZNSt16coroutine_handleIvE7addressEv(%"struct.std::coroutine_handle"* {{[^,]*}} %[[TMP]])
+  // CHECK: %[[ADDR:.+]] = call i8* @_ZNSt12experimental16coroutine_handleIvE7addressEv(%"struct.std::experimental::coroutine_handle"* {{[^,]*}} %[[TMP]])
   // CHECK: call void @llvm.coro.resume(i8* %[[ADDR]])
 }
diff --git a/clang/test/CodeGenCoroutines/coro-cleanup.cpp b/clang/test/CodeGenCoroutines/coro-cleanup.cpp
--- a/clang/test/CodeGenCoroutines/coro-cleanup.cpp
+++ b/clang/test/CodeGenCoroutines/coro-cleanup.cpp
@@ -1,7 +1,7 @@
 // Verify that coroutine promise and allocated memory are freed up on exception.
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -14,15 +14,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <> struct std::coroutine_traits<void> {
+template <> struct std::experimental::coroutine_traits<void> {
   struct promise_type {
     void get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
@@ -43,7 +43,7 @@
 
   // If promise constructor throws, check that we free the memory.
 
-  // CHECK: invoke void @_ZNSt16coroutine_traitsIJvEE12promise_typeC1Ev(
+  // CHECK: invoke void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_typeC1Ev(
   // CHECK-NEXT: to label %{{.+}} unwind label %[[DeallocPad:.+]]
 
   // CHECK: [[DeallocPad]]:
@@ -67,7 +67,7 @@
 
   // CHECK: [[Catch]]:
   // CHECK:    call i8* @__cxa_begin_catch(
-  // CHECK:    call void @_ZNSt16coroutine_traitsIJvEE12promise_type19unhandled_exceptionEv(
+  // CHECK:    call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type19unhandled_exceptionEv(
   // CHECK:    invoke void @__cxa_end_catch()
   // CHECK-NEXT:    to label %[[Cont:.+]] unwind
 
@@ -77,7 +77,7 @@
   // CHECK-NEXT: br label %[[Cleanup:.+]]
 
   // CHECK: [[Cleanup]]:
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvEE12promise_typeD1Ev(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_typeD1Ev(
   // CHECK: %[[Mem0:.+]] = call i8* @llvm.coro.free(
   // CHECK: call void @_ZdlPv(i8* %[[Mem0]]
 
@@ -93,5 +93,5 @@
   for (;;)
     co_await suspend_always{};
   // Since this is the endless loop there should be no fallthrough handler (call to 'return_void').
-  // CHECK-NOT: call void @_ZNSt16coroutine_traitsIJvEE12promise_type11return_voidEv
+  // CHECK-NOT: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type11return_voidEv
 }
diff --git a/clang/test/CodeGenCoroutines/coro-dest-slot.cpp b/clang/test/CodeGenCoroutines/coro-dest-slot.cpp
--- a/clang/test/CodeGenCoroutines/coro-dest-slot.cpp
+++ b/clang/test/CodeGenCoroutines/coro-dest-slot.cpp
@@ -2,7 +2,7 @@
 
 #include "Inputs/coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
 
 struct coro {
   struct promise_type {
@@ -30,7 +30,7 @@
 // CHECK-NEXT:   i8 1, label %[[FINAL_CLEANUP:.+]]
 // CHECK-NEXT: ]
 
-// CHECK: call void @_ZNSt13suspend_never12await_resumeEv(
+// CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(
 // CHECK: %[[CLEANUP_DEST1:.+]] = phi i32 [ 0, %[[FINAL_READY]] ], [ 2, %[[FINAL_CLEANUP]] ]
 // CHECK: %[[CLEANUP_DEST2:.+]] = phi i32 [ %[[CLEANUP_DEST0]], %{{.+}} ], [ %[[CLEANUP_DEST1]], %{{.+}} ], [ 0, %{{.+}} ]
 // CHECK: call i8* @llvm.coro.free(
diff --git a/clang/test/CodeGenCoroutines/coro-dwarf.cpp b/clang/test/CodeGenCoroutines/coro-dwarf.cpp
--- a/clang/test/CodeGenCoroutines/coro-dwarf.cpp
+++ b/clang/test/CodeGenCoroutines/coro-dwarf.cpp
@@ -3,7 +3,7 @@
 // RUN:            -emit-llvm -o - %s | \
 // RUN:            FileCheck %s --implicit-check-not=DILocalVariable
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -16,15 +16,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+} // namespace std::experimental
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <typename... Args> struct std::coroutine_traits<void, Args...> {
+template <typename... Args> struct std::experimental::coroutine_traits<void, Args...> {
   struct promise_type {
     void get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
diff --git a/clang/test/CodeGenCoroutines/coro-eh-cleanup.cpp b/clang/test/CodeGenCoroutines/coro-eh-cleanup.cpp
--- a/clang/test/CodeGenCoroutines/coro-eh-cleanup.cpp
+++ b/clang/test/CodeGenCoroutines/coro-eh-cleanup.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-pc-windows-msvc18.0.0 -emit-llvm %s -o - -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck --check-prefix=CHECK-LPAD %s
 
-namespace std {
+namespace std::experimental {
 template <typename R, typename... T> struct coroutine_traits {
   using promise_type = typename R::promise_type;
 };
@@ -18,11 +18,11 @@
   coroutine_handle() = default;
   static coroutine_handle from_address(void *) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
diff --git a/clang/test/CodeGenCoroutines/coro-gro-nrvo.cpp b/clang/test/CodeGenCoroutines/coro-gro-nrvo.cpp
--- a/clang/test/CodeGenCoroutines/coro-gro-nrvo.cpp
+++ b/clang/test/CodeGenCoroutines/coro-gro-nrvo.cpp
@@ -2,7 +2,7 @@
 
 #include "Inputs/coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
 
 namespace std {
 
diff --git a/clang/test/CodeGenCoroutines/coro-gro.cpp b/clang/test/CodeGenCoroutines/coro-gro.cpp
--- a/clang/test/CodeGenCoroutines/coro-gro.cpp
+++ b/clang/test/CodeGenCoroutines/coro-gro.cpp
@@ -2,7 +2,7 @@
 // Verify that coroutine promise and allocated memory are freed up on exception.
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -disable-llvm-passes | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -15,11 +15,11 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
@@ -28,7 +28,7 @@
   operator int() noexcept;
 };
 
-template <> struct std::coroutine_traits<int> {
+template <> struct std::experimental::coroutine_traits<int> {
   struct promise_type {
     GroType get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
@@ -51,8 +51,8 @@
   // CHECK: %[[Size:.+]] = call i64 @llvm.coro.size.i64()
   // CHECK: call noalias nonnull i8* @_Znwm(i64 %[[Size]])
   // CHECK: store i1 false, i1* %[[GroActive]]
-  // CHECK: call void @_ZNSt16coroutine_traitsIJiEE12promise_typeC1Ev(
-  // CHECK: call void @_ZNSt16coroutine_traitsIJiEE12promise_type17get_return_objectEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJiEE12promise_typeC1Ev(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJiEE12promise_type17get_return_objectEv(
   // CHECK: store i1 true, i1* %[[GroActive]]
 
   Cleanup cleanup;
@@ -60,12 +60,12 @@
   co_return;
 
   // CHECK: call void @_Z11doSomethingv(
-  // CHECK: call void @_ZNSt16coroutine_traitsIJiEE12promise_type11return_voidEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJiEE12promise_type11return_voidEv(
   // CHECK: call void @_ZN7CleanupD1Ev(
 
   // Destroy promise and free the memory.
 
-  // CHECK: call void @_ZNSt16coroutine_traitsIJiEE12promise_typeD1Ev(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJiEE12promise_typeD1Ev(
   // CHECK: %[[Mem:.+]] = call i8* @llvm.coro.free(
   // CHECK: call void @_ZdlPv(i8* %[[Mem]])
 
diff --git a/clang/test/CodeGenCoroutines/coro-lambda.cpp b/clang/test/CodeGenCoroutines/coro-lambda.cpp
--- a/clang/test/CodeGenCoroutines/coro-lambda.cpp
+++ b/clang/test/CodeGenCoroutines/coro-lambda.cpp
@@ -1,7 +1,7 @@
 // Verify that we synthesized the coroutine for a lambda inside of a function template.
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename R, typename... T> struct coroutine_traits {
   using promise_type = typename R::promise_type;
 };
@@ -17,11 +17,11 @@
   coroutine_handle() = default;
   static coroutine_handle from_address(void *) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
diff --git a/clang/test/CodeGenCoroutines/coro-newpm-pipeline.cpp b/clang/test/CodeGenCoroutines/coro-newpm-pipeline.cpp
--- a/clang/test/CodeGenCoroutines/coro-newpm-pipeline.cpp
+++ b/clang/test/CodeGenCoroutines/coro-newpm-pipeline.cpp
@@ -16,6 +16,7 @@
 // CHECK-ALL: Running pass:{{.*}}CoroCleanupPass
 
 namespace std {
+namespace experimental {
 
 struct handle {};
 
@@ -38,6 +39,7 @@
     void unhandled_exception() {}
   };
 };
+} // namespace experimental
 } // namespace std
 
 void foo() { co_return; }
diff --git a/clang/test/CodeGenCoroutines/coro-params.cpp b/clang/test/CodeGenCoroutines/coro-params.cpp
--- a/clang/test/CodeGenCoroutines/coro-params.cpp
+++ b/clang/test/CodeGenCoroutines/coro-params.cpp
@@ -4,7 +4,7 @@
 // Verifies that parameter copies are used to construct the promise type, if that type has a matching constructor
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -disable-llvm-passes -fexceptions | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -17,15 +17,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <typename... Args> struct std::coroutine_traits<void, Args...> {
+template <typename... Args> struct std::experimental::coroutine_traits<void, Args...> {
   struct promise_type {
     void get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
@@ -73,9 +73,9 @@
   // CHECK-NEXT: bitcast %struct.MoveAndCopy* %[[McCopy]] to i8*
   // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(
   // CHECK-NEXT: call void @_ZN11MoveAndCopyC1EOS_(%struct.MoveAndCopy* {{[^,]*}} %[[McCopy]], %struct.MoveAndCopy* nonnull align 4 dereferenceable(4) %[[McParam]]) #
-  // CHECK-NEXT: bitcast %"struct.std::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* %__promise to i8*
+  // CHECK-NEXT: bitcast %"struct.std::experimental::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* %__promise to i8*
   // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(
-  // CHECK-NEXT: invoke void @_ZNSt16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_typeC1Ev(
+  // CHECK-NEXT: invoke void @_ZNSt12experimental16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_typeC1Ev(
 
   // CHECK: call void @_ZN14suspend_always12await_resumeEv(
   // CHECK: %[[IntParam:.+]] = load i32, i32* %{{.*}}
@@ -89,12 +89,12 @@
   co_return;
 
   // Skip to final suspend:
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_type13final_suspendEv(
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_type13final_suspendEv(
   // CHECK: call void @_ZN14suspend_always12await_resumeEv(
 
   // Destroy promise, then parameter copies:
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_typeD1Ev(%"struct.std::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* {{[^,]*}} %__promise)
-  // CHECK-NEXT: bitcast %"struct.std::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* %__promise to i8*
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvi8MoveOnly11MoveAndCopyEE12promise_typeD1Ev(%"struct.std::experimental::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* {{[^,]*}} %__promise)
+  // CHECK-NEXT: bitcast %"struct.std::experimental::coroutine_traits<void, int, MoveOnly, MoveAndCopy>::promise_type"* %__promise to i8*
   // CHECK-NEXT: call void @llvm.lifetime.end.p0i8(
   // CHECK-NEXT: call void @_ZN11MoveAndCopyD1Ev(%struct.MoveAndCopy* {{[^,]*}} %[[McCopy]])
   // CHECK-NEXT: bitcast %struct.MoveAndCopy* %[[McCopy]] to i8*
@@ -124,9 +124,9 @@
   // CHECK-NEXT: bitcast %struct.B* %[[y_copy]] to i8*
   // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(
   // CHECK-NEXT: call void @_ZN1BC1EOS_(%struct.B* {{[^,]*}} %[[y_copy]], %struct.B* nonnull align 4 dereferenceable(512) %y)
-  // CHECK-NEXT: bitcast %"struct.std::coroutine_traits<void, A, B, B>::promise_type"* %__promise to i8*
+  // CHECK-NEXT: bitcast %"struct.std::experimental::coroutine_traits<void, A, B, B>::promise_type"* %__promise to i8*
   // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(
-  // CHECK-NEXT: invoke void @_ZNSt16coroutine_traitsIJv1A1BS1_EE12promise_typeC1Ev(
+  // CHECK-NEXT: invoke void @_ZNSt12experimental16coroutine_traitsIJv1A1BS2_EE12promise_typeC1Ev(
 
   co_return;
 }
@@ -155,8 +155,8 @@
 
 struct promise_matching_constructor {};
 
-template <>
-struct std::coroutine_traits<void, promise_matching_constructor, int, float, double> {
+template<>
+struct std::experimental::coroutine_traits<void, promise_matching_constructor, int, float, double> {
   struct promise_type {
     promise_type(promise_matching_constructor, int, float, double) {}
     promise_type() = delete;
@@ -173,7 +173,7 @@
   // CHECK: %[[INT:.+]] = load i32, i32* %5, align 4
   // CHECK: %[[FLOAT:.+]] = load float, float* %6, align 4
   // CHECK: %[[DOUBLE:.+]] = load double, double* %7, align 8
-  // CHECK: invoke void @_ZNSt16coroutine_traitsIJv28promise_matching_constructorifdEE12promise_typeC1ES0_ifd(%"struct.std::coroutine_traits<void, promise_matching_constructor, int, float, double>::promise_type"* {{[^,]*}} %__promise, i32 %[[INT]], float %[[FLOAT]], double %[[DOUBLE]])
+  // CHECK: invoke void @_ZNSt12experimental16coroutine_traitsIJv28promise_matching_constructorifdEE12promise_typeC1ES1_ifd(%"struct.std::experimental::coroutine_traits<void, promise_matching_constructor, int, float, double>::promise_type"* {{[^,]*}} %__promise, i32 %[[INT]], float %[[FLOAT]], double %[[DOUBLE]])
   co_return;
 }
 
@@ -181,7 +181,7 @@
 
 struct method {};
 
-template <typename... Args> struct std::coroutine_traits<method, Args...> {
+template <typename... Args> struct std::experimental::coroutine_traits<method, Args...> {
   struct promise_type {
     promise_type(some_class&, float);
     method get_return_object();
@@ -198,6 +198,6 @@
 
 // CHECK-LABEL: define{{.*}} void @_ZN10some_class39good_coroutine_calls_custom_constructorEf(%struct.some_class*
 method some_class::good_coroutine_calls_custom_constructor(float) {
-  // CHECK: invoke void @_ZNSt16coroutine_traitsIJ6methodR10some_classfEE12promise_typeC1ES2_f(%"struct.std::coroutine_traits<method, some_class &, float>::promise_type"* {{[^,]*}} %__promise, %struct.some_class* nonnull align 1 dereferenceable(1) %{{.+}}, float
+  // CHECK: invoke void @_ZNSt12experimental16coroutine_traitsIJ6methodR10some_classfEE12promise_typeC1ES3_f(%"struct.std::experimental::coroutine_traits<method, some_class &, float>::promise_type"* {{[^,]*}} %__promise, %struct.some_class* nonnull align 1 dereferenceable(1) %{{.+}}, float
   co_return;
 }
diff --git a/clang/test/CodeGenCoroutines/coro-promise-dtor.cpp b/clang/test/CodeGenCoroutines/coro-promise-dtor.cpp
--- a/clang/test/CodeGenCoroutines/coro-promise-dtor.cpp
+++ b/clang/test/CodeGenCoroutines/coro-promise-dtor.cpp
@@ -3,13 +3,15 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 struct coro_t {
   void* p;
   ~coro_t();
   struct promise_type {
     coro_t get_return_object();
-    std::suspend_never initial_suspend();
-    std::suspend_never final_suspend() noexcept;
+    coro::suspend_never initial_suspend();
+    coro::suspend_never final_suspend() noexcept;
     void return_void();
     promise_type();
     ~promise_type();
diff --git a/clang/test/CodeGenCoroutines/coro-ret-void.cpp b/clang/test/CodeGenCoroutines/coro-ret-void.cpp
--- a/clang/test/CodeGenCoroutines/coro-ret-void.cpp
+++ b/clang/test/CodeGenCoroutines/coro-ret-void.cpp
@@ -2,21 +2,23 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 struct coro1 {
   struct promise_type {
     coro1 get_return_object();
-    std::suspend_never initial_suspend();
-    std::suspend_never final_suspend() noexcept;
+    coro::suspend_never initial_suspend();
+    coro::suspend_never final_suspend() noexcept;
     void return_void();
   };
 };
 
 coro1 f() {
-  co_await std::suspend_never{};
+  co_await coro::suspend_never{};
 }
 
 // CHECK-LABEL: define{{.*}} void @_Z1fv(
-// CHECK: call void @_ZNSt13suspend_never12await_resumeEv(%"struct.std::suspend_never"*
+// CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(%"struct.std::experimental::coroutines_v1::suspend_never"*
 // CHECK: call void @_ZN5coro112promise_type11return_voidEv(%"struct.coro1::promise_type"* {{[^,]*}} %__promise)
 
 struct A {
@@ -36,8 +38,8 @@
 struct coro2 {
   struct promise_type {
     coro2 get_return_object();
-    std::suspend_never initial_suspend();
-    std::suspend_never final_suspend() noexcept;
+    coro::suspend_never initial_suspend();
+    coro::suspend_never final_suspend() noexcept;
     void return_value(int);
   };
 };
@@ -47,5 +49,5 @@
 }
 
 // CHECK-LABEL: define{{.*}} void @_Z1gv(
-// CHECK: call void @_ZNSt13suspend_never12await_resumeEv(%"struct.std::suspend_never"*
+// CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(%"struct.std::experimental::coroutines_v1::suspend_never"*
 // CHECK: call void @_ZN5coro212promise_type12return_valueEi(%"struct.coro2::promise_type"* {{[^,]*}} %__promise, i32 42)
diff --git a/clang/test/CodeGenCoroutines/coro-return-voidtype-initlist.cpp b/clang/test/CodeGenCoroutines/coro-return-voidtype-initlist.cpp
--- a/clang/test/CodeGenCoroutines/coro-return-voidtype-initlist.cpp
+++ b/clang/test/CodeGenCoroutines/coro-return-voidtype-initlist.cpp
@@ -5,6 +5,7 @@
 struct b { b(int, a); };
 template <typename, typename = int>
 struct c {};
+namespace experimental {
 template <typename d>
 struct coroutine_traits : d {};
 template <typename = void>
@@ -20,6 +21,7 @@
   void await_suspend(coroutine_handle<>);
   void await_resume();
 };
+} // namespace experimental
 } // namespace std
 template <typename ag>
 auto ah(ag) { return ag().ah(0); }
@@ -29,10 +31,10 @@
   struct h {
     int await_ready() noexcept;
     template <typename al>
-    void await_suspend(std::coroutine_handle<al>) noexcept;
+    void await_suspend(std::experimental::coroutine_handle<al>) noexcept;
     void await_resume() noexcept;
   };
-  std::e initial_suspend();
+  std::experimental::e initial_suspend();
   h final_suspend() noexcept;
   template <typename ag>
   auto await_transform(ag) { return ah(ag()); }
@@ -43,20 +45,20 @@
   void unhandled_exception();
 };
 struct k {
-  k(std::coroutine_handle<>);
+  k(std::experimental::coroutine_handle<>);
   int await_ready();
 };
 template <typename am>
 struct f {
   using promise_type = j;
-  std::coroutine_handle<> ar;
+  std::experimental::coroutine_handle<> ar;
   struct l : k {
     using at = k;
-    l(std::coroutine_handle<> m) : at(m) {}
-    void await_suspend(std::coroutine_handle<>);
+    l(std::experimental::coroutine_handle<> m) : at(m) {}
+    void await_suspend(std::experimental::coroutine_handle<>);
   };
   struct n : l {
-    n(std::coroutine_handle<> m) : l(m) {}
+    n(std::experimental::coroutine_handle<> m) : l(m) {}
     am await_resume();
   };
   auto ah(int) { return n(ar); }
diff --git a/clang/test/CodeGenCoroutines/coro-return.cpp b/clang/test/CodeGenCoroutines/coro-return.cpp
--- a/clang/test/CodeGenCoroutines/coro-return.cpp
+++ b/clang/test/CodeGenCoroutines/coro-return.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++1z -emit-llvm %s -o - -disable-llvm-passes | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -13,15 +13,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept {}
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <> struct std::coroutine_traits<void> {
+template <> struct std::experimental::coroutine_traits<void> {
   struct promise_type {
     void get_return_object();
     suspend_always initial_suspend();
@@ -32,15 +32,15 @@
 
 // CHECK-LABEL: f0(
 extern "C" void f0() {
-  // CHECK: %__promise = alloca %"struct.std::coroutine_traits<void>::promise_type"
+  // CHECK: %__promise = alloca %"struct.std::experimental::coroutine_traits<void>::promise_type"
   // CHECK: %call = call noalias nonnull i8* @_Znwm(
-  // CHECK: call void @_ZNSt16coroutine_traitsIJvEE12promise_type11return_voidEv(%"struct.std::coroutine_traits<void>::promise_type"* {{[^,]*}} %__promise)
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type11return_voidEv(%"struct.std::experimental::coroutine_traits<void>::promise_type"* {{[^,]*}} %__promise)
   // CHECK: call void @_ZdlPv
   co_return;
 }
 
-template <>
-struct std::coroutine_traits<int> {
+template<>
+struct std::experimental::coroutine_traits<int> {
   struct promise_type {
     int get_return_object();
     suspend_always initial_suspend();
@@ -51,9 +51,9 @@
 
 // CHECK-LABEL: f1(
 extern "C" int f1() {
-  // CHECK: %__promise = alloca %"struct.std::coroutine_traits<int>::promise_type"
+  // CHECK: %__promise = alloca %"struct.std::experimental::coroutine_traits<int>::promise_type"
   // CHECK: %call = call noalias nonnull i8* @_Znwm(
-  // CHECK: call void @_ZNSt16coroutine_traitsIJiEE12promise_type12return_valueEi(%"struct.std::coroutine_traits<int>::promise_type"* {{[^,]*}} %__promise, i32 42)
+  // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJiEE12promise_type12return_valueEi(%"struct.std::experimental::coroutine_traits<int>::promise_type"* {{[^,]*}} %__promise, i32 42)
   // CHECK: call void @_ZdlPv
   co_return 42;
 }
diff --git a/clang/test/CodeGenCoroutines/coro-symmetric-transfer-01.cpp b/clang/test/CodeGenCoroutines/coro-symmetric-transfer-01.cpp
--- a/clang/test/CodeGenCoroutines/coro-symmetric-transfer-01.cpp
+++ b/clang/test/CodeGenCoroutines/coro-symmetric-transfer-01.cpp
@@ -3,17 +3,19 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 struct detached_task {
   struct promise_type {
     detached_task get_return_object() noexcept {
-      return detached_task{std::coroutine_handle<promise_type>::from_promise(*this)};
+      return detached_task{coro::coroutine_handle<promise_type>::from_promise(*this)};
     }
 
     void return_void() noexcept {}
 
     struct final_awaiter {
       bool await_ready() noexcept { return false; }
-      std::coroutine_handle<> await_suspend(std::coroutine_handle<promise_type> h) noexcept {
+      coro::coroutine_handle<> await_suspend(coro::coroutine_handle<promise_type> h) noexcept {
         h.destroy();
         return {};
       }
@@ -24,7 +26,7 @@
 
     final_awaiter final_suspend() noexcept { return {}; }
 
-    std::suspend_always initial_suspend() noexcept { return {}; }
+    coro::suspend_always initial_suspend() noexcept { return {}; }
   };
 
   ~detached_task() {
@@ -40,7 +42,7 @@
     tmp.resume();
   }
 
-  std::coroutine_handle<promise_type> coro_;
+  coro::coroutine_handle<promise_type> coro_;
 };
 
 detached_task foo() {
@@ -50,12 +52,12 @@
 // check that the lifetime of the coroutine handle used to obtain the address is contained within single basic block, and hence does not live across suspension points.
 // CHECK-LABEL: final.suspend:
 // CHECK:         %{{.+}} = call token @llvm.coro.save(i8* null)
-// CHECK:         %[[HDL_CAST1:.+]] = bitcast %"struct.std::coroutine_handle.0"* %[[HDL:.+]] to i8*
+// CHECK:         %[[HDL_CAST1:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle.0"* %[[HDL:.+]] to i8*
 // CHECK:         call void @llvm.lifetime.start.p0i8(i64 8, i8* %[[HDL_CAST1]])
-// CHECK:         %[[CALL:.+]] = call i8* @_ZN13detached_task12promise_type13final_awaiter13await_suspendESt16coroutine_handleIS0_E(
-// CHECK:         %[[HDL_CAST2:.+]] = getelementptr inbounds %"struct.std::coroutine_handle.0", %"struct.std::coroutine_handle.0"* %[[HDL]], i32 0, i32 0
+// CHECK:         %[[CALL:.+]] = call i8* @_ZN13detached_task12promise_type13final_awaiter13await_suspendENSt12experimental13coroutines_v116coroutine_handleIS0_EE(
+// CHECK:         %[[HDL_CAST2:.+]] = getelementptr inbounds %"struct.std::experimental::coroutines_v1::coroutine_handle.0", %"struct.std::experimental::coroutines_v1::coroutine_handle.0"* %[[HDL]], i32 0, i32 0
 // CHECK:         store i8* %[[CALL]], i8** %[[HDL_CAST2]], align 8
-// CHECK:         %[[HDL_TRANSFER:.+]] = call i8* @_ZNKSt16coroutine_handleIvE7addressEv(%"struct.std::coroutine_handle.0"* nonnull align 8 dereferenceable(8) %[[HDL]])
-// CHECK:         %[[HDL_CAST3:.+]] = bitcast %"struct.std::coroutine_handle.0"* %[[HDL]] to i8*
+// CHECK:         %[[HDL_TRANSFER:.+]] = call i8* @_ZNKSt12experimental13coroutines_v116coroutine_handleIvE7addressEv(%"struct.std::experimental::coroutines_v1::coroutine_handle.0"* nonnull align 8 dereferenceable(8) %[[HDL]])
+// CHECK:         %[[HDL_CAST3:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle.0"* %[[HDL]] to i8*
 // CHECK:         call void @llvm.lifetime.end.p0i8(i64 8, i8* %[[HDL_CAST3]])
 // CHECK:         call void @llvm.coro.resume(i8* %[[HDL_TRANSFER]])
diff --git a/clang/test/CodeGenCoroutines/coro-symmetric-transfer-02.cpp b/clang/test/CodeGenCoroutines/coro-symmetric-transfer-02.cpp
--- a/clang/test/CodeGenCoroutines/coro-symmetric-transfer-02.cpp
+++ b/clang/test/CodeGenCoroutines/coro-symmetric-transfer-02.cpp
@@ -2,17 +2,19 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 struct Task {
   struct promise_type {
     Task get_return_object() noexcept {
-      return Task{std::coroutine_handle<promise_type>::from_promise(*this)};
+      return Task{coro::coroutine_handle<promise_type>::from_promise(*this)};
     }
 
     void return_void() noexcept {}
 
     struct final_awaiter {
       bool await_ready() noexcept { return false; }
-      std::coroutine_handle<> await_suspend(std::coroutine_handle<promise_type> h) noexcept {
+      coro::coroutine_handle<> await_suspend(coro::coroutine_handle<promise_type> h) noexcept {
         h.destroy();
         return {};
       }
@@ -23,7 +25,7 @@
 
     final_awaiter final_suspend() noexcept { return {}; }
 
-    std::suspend_always initial_suspend() noexcept { return {}; }
+    coro::suspend_always initial_suspend() noexcept { return {}; }
 
     template <typename Awaitable>
     auto await_transform(Awaitable &&awaitable) {
@@ -31,7 +33,7 @@
     }
   };
 
-  using handle_t = std::coroutine_handle<promise_type>;
+  using handle_t = coro::coroutine_handle<promise_type>;
 
   class Awaiter {
   public:
@@ -41,7 +43,7 @@
     ~Awaiter();
 
     bool await_ready() noexcept { return false; }
-    handle_t await_suspend(std::coroutine_handle<> continuation) noexcept;
+    handle_t await_suspend(coro::coroutine_handle<> continuation) noexcept;
     void await_resume();
 
   private:
@@ -89,10 +91,10 @@
 // CHECK:         br i1 %{{.+}}, label %[[CASE1_AWAIT_READY:.+]], label %[[CASE1_AWAIT_SUSPEND:.+]]
 // CHECK:       [[CASE1_AWAIT_SUSPEND]]:
 // CHECK-NEXT:    %{{.+}} = call token @llvm.coro.save(i8* null)
-// CHECK-NEXT:    %[[HANDLE11:.+]] = bitcast %"struct.std::coroutine_handle"* %[[TMP1:.+]] to i8*
+// CHECK-NEXT:    %[[HANDLE11:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle"* %[[TMP1:.+]] to i8*
 // CHECK-NEXT:    call void @llvm.lifetime.start.p0i8(i64 8, i8* %[[HANDLE11]])
 
-// CHECK:         %[[HANDLE12:.+]] = bitcast %"struct.std::coroutine_handle"* %[[TMP1]] to i8*
+// CHECK:         %[[HANDLE12:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle"* %[[TMP1]] to i8*
 // CHECK-NEXT:    call void @llvm.lifetime.end.p0i8(i64 8, i8* %[[HANDLE12]])
 // CHECK-NEXT:    call void @llvm.coro.resume
 // CHECK-NEXT:    %{{.+}} = call i8 @llvm.coro.suspend
@@ -108,10 +110,10 @@
 // CHECK:         br i1 %{{.+}}, label %[[CASE2_AWAIT_READY:.+]], label %[[CASE2_AWAIT_SUSPEND:.+]]
 // CHECK:       [[CASE2_AWAIT_SUSPEND]]:
 // CHECK-NEXT:    %{{.+}} = call token @llvm.coro.save(i8* null)
-// CHECK-NEXT:    %[[HANDLE21:.+]] = bitcast %"struct.std::coroutine_handle"* %[[TMP2:.+]] to i8*
+// CHECK-NEXT:    %[[HANDLE21:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle"* %[[TMP2:.+]] to i8*
 // CHECK-NEXT:    call void @llvm.lifetime.start.p0i8(i64 8, i8* %[[HANDLE21]])
 
-// CHECK:         %[[HANDLE22:.+]] = bitcast %"struct.std::coroutine_handle"* %[[TMP2]] to i8*
+// CHECK:         %[[HANDLE22:.+]] = bitcast %"struct.std::experimental::coroutines_v1::coroutine_handle"* %[[TMP2]] to i8*
 // CHECK-NEXT:    call void @llvm.lifetime.end.p0i8(i64 8, i8* %[[HANDLE22]])
 // CHECK-NEXT:    call void @llvm.coro.resume
 // CHECK-NEXT:    %{{.+}} = call i8 @llvm.coro.suspend
diff --git a/clang/test/CodeGenCoroutines/coro-unhandled-exception.cpp b/clang/test/CodeGenCoroutines/coro-unhandled-exception.cpp
--- a/clang/test/CodeGenCoroutines/coro-unhandled-exception.cpp
+++ b/clang/test/CodeGenCoroutines/coro-unhandled-exception.cpp
@@ -3,6 +3,8 @@
 
 #include "Inputs/coroutine.h"
 
+namespace coro = std::experimental::coroutines_v1;
+
 namespace std {
   using exception_ptr = int;
   exception_ptr current_exception();
@@ -11,11 +13,11 @@
 struct coro_t {
   struct promise_type {
     coro_t get_return_object() {
-      std::coroutine_handle<promise_type>{};
+      coro::coroutine_handle<promise_type>{};
       return {};
     }
-    std::suspend_never initial_suspend() { return {}; }
-    std::suspend_never final_suspend() noexcept { return {}; }
+    coro::suspend_never initial_suspend() { return {}; }
+    coro::suspend_never final_suspend() noexcept { return {}; }
     void return_void(){}
     void unhandled_exception() noexcept;
   };
@@ -48,9 +50,9 @@
 // CHECK: [[TRYCONT]]:
 // CHECK-NEXT: br label %[[COROFIN:.+]]
 // CHECK: [[COROFIN]]:
-// CHECK-NEXT: bitcast %"struct.std::suspend_never"* %{{.+}} to i8*
+// CHECK-NEXT: bitcast %"struct.std::experimental::coroutines_v1::suspend_never"* %{{.+}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(
-// CHECK-NEXT: call void @"?final_suspend@promise_type@coro_t@@QEAA?AUsuspend_never@std@@XZ"(
+// CHECK-NEXT: call void @"?final_suspend@promise_type@coro_t@@QEAA?AUsuspend_never@coroutines_v1@experimental@std@@XZ"(
 
 // CHECK-LPAD: @_Z1fv(
 // CHECK-LPAD:   invoke void @_Z9may_throwv()
@@ -69,6 +71,6 @@
 // CHECK-LPAD: [[TRYCONT]]:
 // CHECK-LPAD: br label %[[COROFIN:.+]]
 // CHECK-LPAD: [[COROFIN]]:
-// CHECK-LPAD-NEXT: bitcast %"struct.std::suspend_never"* %{{.+}} to i8*
+// CHECK-LPAD-NEXT: bitcast %"struct.std::experimental::coroutines_v1::suspend_never"* %{{.+}} to i8*
 // CHECK-LPAD-NEXT: call void @llvm.lifetime.start.p0i8(
 // CHECK-LPAD-NEXT: call void @_ZN6coro_t12promise_type13final_suspendEv(
diff --git a/clang/test/CoverageMapping/coroutine.cpp b/clang/test/CoverageMapping/coroutine.cpp
--- a/clang/test/CoverageMapping/coroutine.cpp
+++ b/clang/test/CoverageMapping/coroutine.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++14 -emit-llvm -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping %s -o - | FileCheck %s
 
-namespace std {
+namespace std::experimental {
 template <typename... T>
 struct coroutine_traits;
 
@@ -16,16 +16,16 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept {}
 };
-} // namespace std
+} // namespace std::experimental
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
 template <>
-struct std::coroutine_traits<int, int> {
+struct std::experimental::coroutine_traits<int, int> {
   struct promise_type {
     int get_return_object();
     suspend_always initial_suspend();
diff --git a/clang/test/Index/coroutines.cpp b/clang/test/Index/coroutines.cpp
--- a/clang/test/Index/coroutines.cpp
+++ b/clang/test/Index/coroutines.cpp
@@ -1,8 +1,8 @@
 // RUN: c-index-test -test-load-source all -c %s -fsyntax-only -target x86_64-apple-darwin9 -fcoroutines-ts -std=c++1z -I%S/../SemaCXX/Inputs | FileCheck %s
 #include "std-coroutine.h"
 
-using std::suspend_always;
-using std::suspend_never;
+using std::experimental::suspend_always;
+using std::experimental::suspend_never;
 
 struct promise_void {
   void get_return_object();
@@ -13,7 +13,7 @@
 };
 
 template <>
-struct std::coroutine_traits<void> { using promise_type = promise_void; };
+struct std::experimental::coroutine_traits<void> { using promise_type = promise_void; };
 
 void CoroutineTestRet() {
   co_return;
diff --git a/clang/test/PCH/coroutines.cpp b/clang/test/PCH/coroutines.cpp
--- a/clang/test/PCH/coroutines.cpp
+++ b/clang/test/PCH/coroutines.cpp
@@ -8,7 +8,7 @@
 #ifndef HEADER
 #define HEADER
 
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -21,15 +21,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <typename... Args> struct std::coroutine_traits<void, Args...> {
+template <typename... Args> struct std::experimental::coroutine_traits<void, Args...> {
   struct promise_type {
     void get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
@@ -42,7 +42,7 @@
   };
 };
 
-template <typename... Args> struct std::coroutine_traits<int, Args...> {
+template <typename... Args> struct std::experimental::coroutine_traits<int, Args...> {
   struct promise_type {
     int get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
diff --git a/clang/test/SemaCXX/Inputs/std-coroutine.h b/clang/test/SemaCXX/Inputs/std-coroutine.h
--- a/clang/test/SemaCXX/Inputs/std-coroutine.h
+++ b/clang/test/SemaCXX/Inputs/std-coroutine.h
@@ -3,6 +3,7 @@
 #define STD_COROUTINE_H
 
 namespace std {
+namespace experimental {
 
 template <class Ret, typename... T>
 struct coroutine_traits { using promise_type = typename Ret::promise_type; };
@@ -30,6 +31,7 @@
   void await_resume() noexcept {}
 };
 
+} // namespace experimental
 } // namespace std
 
 #endif // STD_COROUTINE_H
diff --git a/clang/test/SemaCXX/co_await-range-for.cpp b/clang/test/SemaCXX/co_await-range-for.cpp
--- a/clang/test/SemaCXX/co_await-range-for.cpp
+++ b/clang/test/SemaCXX/co_await-range-for.cpp
@@ -3,7 +3,8 @@
 // RUN:    -fblocks
 #include "Inputs/std-coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
+
 
 template <class Begin>
 struct Awaiter {
diff --git a/clang/test/SemaCXX/coreturn-eh.cpp b/clang/test/SemaCXX/coreturn-eh.cpp
--- a/clang/test/SemaCXX/coreturn-eh.cpp
+++ b/clang/test/SemaCXX/coreturn-eh.cpp
@@ -3,12 +3,12 @@
 
 #include "Inputs/std-coroutine.h"
 
-using std::suspend_always;
-using std::suspend_never;
+using std::experimental::suspend_always;
+using std::experimental::suspend_never;
 
 struct awaitable {
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>); // FIXME: coroutine_handle
+  void await_suspend(std::experimental::coroutine_handle<>); // FIXME: coroutine_handle
   void await_resume();
 } a;
 
@@ -33,7 +33,7 @@
 };
 
 template <typename T1>
-struct std::coroutine_traits<void, T1> { using promise_type = promise_void_return_value; };
+struct std::experimental::coroutine_traits<void, T1> { using promise_type = promise_void_return_value; };
 
 VoidTagReturnValue test() {
   object x = {};
diff --git a/clang/test/SemaCXX/coreturn.cpp b/clang/test/SemaCXX/coreturn.cpp
--- a/clang/test/SemaCXX/coreturn.cpp
+++ b/clang/test/SemaCXX/coreturn.cpp
@@ -1,12 +1,12 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++14 -fcoroutines-ts -fsyntax-only -Wignored-qualifiers -Wno-error=return-type -verify -fblocks -Wall -Wextra -Wno-error=unreachable-code
 #include "Inputs/std-coroutine.h"
 
-using std::suspend_always;
-using std::suspend_never;
+using std::experimental::suspend_always;
+using std::experimental::suspend_never;
 
 struct awaitable {
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>); // FIXME: coroutine_handle
+  void await_suspend(std::experimental::coroutine_handle<>); // FIXME: coroutine_handle
   void await_resume();
 } a;
 
@@ -72,16 +72,16 @@
 };
 
 template <>
-struct std::coroutine_traits<void> { using promise_type = promise_void; };
+struct std::experimental::coroutine_traits<void> { using promise_type = promise_void; };
 
 template <typename T1>
-struct std::coroutine_traits<void, T1> { using promise_type = promise_void_return_value; };
+struct std::experimental::coroutine_traits<void, T1> { using promise_type = promise_void_return_value; };
 
 template <typename... T>
-struct std::coroutine_traits<float, T...> { using promise_type = promise_float; };
+struct std::experimental::coroutine_traits<float, T...> { using promise_type = promise_float; };
 
 template <typename... T>
-struct std::coroutine_traits<int, T...> { using promise_type = promise_int; };
+struct std::experimental::coroutine_traits<int, T...> { using promise_type = promise_int; };
 
 void test0() { co_await a; }
 float test1() { co_await a; }
diff --git a/clang/test/SemaCXX/coroutine-final-suspend-noexcept.cpp b/clang/test/SemaCXX/coroutine-final-suspend-noexcept.cpp
--- a/clang/test/SemaCXX/coroutine-final-suspend-noexcept.cpp
+++ b/clang/test/SemaCXX/coroutine-final-suspend-noexcept.cpp
@@ -4,6 +4,7 @@
 // RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -verify %s -fcxx-exceptions -fexceptions -Wunused-result
 
 namespace std {
+namespace experimental {
 
 template <class Ret, typename... T>
 struct coroutine_traits { using promise_type = typename Ret::promise_type; };
@@ -33,9 +34,10 @@
   ~suspend_always() noexcept(false); // expected-note 2 {{must be declared with 'noexcept'}}
 };
 
+} // namespace experimental
 } // namespace std
 
-using namespace std;
+using namespace std::experimental;
 
 struct A {
   bool await_ready();
diff --git a/clang/test/SemaCXX/coroutine-rvo.cpp b/clang/test/SemaCXX/coroutine-rvo.cpp
--- a/clang/test/SemaCXX/coroutine-rvo.cpp
+++ b/clang/test/SemaCXX/coroutine-rvo.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -verify -std=c++17 -fcoroutines-ts -fsyntax-only %s
 
-namespace std {
+namespace std::experimental {
 template <class Promise = void> struct coroutine_handle {
   coroutine_handle() = default;
   static coroutine_handle from_address(void *) noexcept;
@@ -30,11 +30,11 @@
 
 template <class Ret, class... Args>
 struct coroutine_traits : public traits_sfinae_base<Ret> {};
-} // namespace std
+}
 
 struct suspend_never {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
diff --git a/clang/test/SemaCXX/coroutine-seh.cpp b/clang/test/SemaCXX/coroutine-seh.cpp
--- a/clang/test/SemaCXX/coroutine-seh.cpp
+++ b/clang/test/SemaCXX/coroutine-seh.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -verify %s -fcxx-exceptions -fexceptions -triple x86_64-windows-msvc -fms-extensions
-namespace std {
+namespace std::experimental {
 template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
@@ -12,15 +12,15 @@
   template <class PromiseType>
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
-} // namespace std
+}
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
-template <> struct std::coroutine_traits<void> {
+template <> struct std::experimental::coroutine_traits<void> {
   struct promise_type {
     void get_return_object() noexcept;
     suspend_always initial_suspend() noexcept;
diff --git a/clang/test/SemaCXX/coroutine-traits-undefined-template.cpp b/clang/test/SemaCXX/coroutine-traits-undefined-template.cpp
--- a/clang/test/SemaCXX/coroutine-traits-undefined-template.cpp
+++ b/clang/test/SemaCXX/coroutine-traits-undefined-template.cpp
@@ -4,14 +4,15 @@
 // RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -verify %s -fcxx-exceptions -fexceptions -Wunused-result
 
 namespace std {
+namespace experimental {
 
 template<typename ...T>
 struct coroutine_traits {
   struct promise_type {};
 };
 
-template <> struct coroutine_traits<void>; // expected-note {{forward declaration of 'std::coroutine_traits<void>'}}
-} // namespace std
+template<> struct coroutine_traits<void>; // expected-note {{forward declaration of 'std::experimental::coroutine_traits<void>'}}
+}} // namespace std::experimental
 
 void uses_forward_declaration() {
   co_return; // expected-error {{this function cannot be a coroutine: missing definition of specialization 'coroutine_traits<void>'}}
diff --git a/clang/test/SemaCXX/coroutine-unhandled_exception-warning.cpp b/clang/test/SemaCXX/coroutine-unhandled_exception-warning.cpp
--- a/clang/test/SemaCXX/coroutine-unhandled_exception-warning.cpp
+++ b/clang/test/SemaCXX/coroutine-unhandled_exception-warning.cpp
@@ -13,8 +13,8 @@
 
 #include "Inputs/std-coroutine.h"
 
-using std::suspend_always;
-using std::suspend_never;
+using std::experimental::suspend_always;
+using std::experimental::suspend_never;
 
 #ifndef DISABLE_WARNING
 struct promise_void { // expected-note {{defined here}}
@@ -28,7 +28,7 @@
 };
 
 template <typename... T>
-struct std::coroutine_traits<void, T...> { using promise_type = promise_void; };
+struct std::experimental::coroutine_traits<void, T...> { using promise_type = promise_void; };
 
 #ifndef DISABLE_WARNING
 void test0() { // expected-warning {{'promise_void' is required to declare the member 'unhandled_exception()' when exceptions are enabled}}
diff --git a/clang/test/SemaCXX/coroutine-uninitialized-warning-crash.cpp b/clang/test/SemaCXX/coroutine-uninitialized-warning-crash.cpp
--- a/clang/test/SemaCXX/coroutine-uninitialized-warning-crash.cpp
+++ b/clang/test/SemaCXX/coroutine-uninitialized-warning-crash.cpp
@@ -1,7 +1,8 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++14 -fcoroutines-ts -fsyntax-only -Wall -Wextra -Wuninitialized  -fblocks
 #include "Inputs/std-coroutine.h"
 
-using namespace std;
+using namespace std::experimental;
+
 
 struct A {
   bool await_ready() { return true; }
diff --git a/clang/test/SemaCXX/coroutine_handle-addres-return-type.cpp b/clang/test/SemaCXX/coroutine_handle-addres-return-type.cpp
--- a/clang/test/SemaCXX/coroutine_handle-addres-return-type.cpp
+++ b/clang/test/SemaCXX/coroutine_handle-addres-return-type.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -verify %s -stdlib=libc++ -std=c++1z -fcoroutines-ts -fsyntax-only
 
-namespace std {
+namespace std::experimental {
 template <class Promise = void>
 struct coroutine_handle;
 
@@ -32,11 +32,11 @@
 
 template <class Ret, class... Args>
 struct coroutine_traits : public traits_sfinae_base<Ret> {};
-} // namespace std
+} // namespace std::experimental
 
 struct suspend_never {
   bool await_ready() noexcept;
-  void await_suspend(std::coroutine_handle<>) noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
@@ -50,18 +50,18 @@
   };
 };
 
-namespace std {
+namespace std::experimental {
 template <>
 struct coroutine_handle<task::promise_type> : public coroutine_handle<> {
   coroutine_handle<task::promise_type> *address() const; // expected-warning {{return type of 'coroutine_handle<>::address should be 'void*'}}
 };
-} // namespace std
+} // namespace std::experimental
 
 struct awaitable {
   bool await_ready();
 
-  std::coroutine_handle<task::promise_type>
-  await_suspend(std::coroutine_handle<> handle);
+  std::experimental::coroutine_handle<task::promise_type>
+  await_suspend(std::experimental::coroutine_handle<> handle);
   void await_resume();
 } a;
 
diff --git a/clang/test/SemaCXX/coroutines-exp-namespace.cpp b/clang/test/SemaCXX/coroutines-exp-namespace.cpp
deleted file mode 100644
--- a/clang/test/SemaCXX/coroutines-exp-namespace.cpp
+++ /dev/null
@@ -1,1450 +0,0 @@
-// This file is the same with coroutines.cpp except the coroutine components are defined in std::experimental namespace.
-// This intention of this test is to make sure the legacy imeplementation in std::experimental namespace could work.
-// TODO: Remove this test once we didn't support
-
-// RUN: %clang_cc1 -std=c++2b                 -fsyntax-only -verify=expected,cxx20_2b,cxx2b    %s -fcxx-exceptions -fexceptions -Wunused-result
-// RUN: %clang_cc1 -std=c++20                 -fsyntax-only -verify=expected,cxx14_20,cxx20_2b %s -fcxx-exceptions -fexceptions -Wunused-result
-// RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -fsyntax-only -verify=expected,cxx14_20          %s -fcxx-exceptions -fexceptions -Wunused-result
-
-void no_coroutine_traits_bad_arg_await() {
-  co_await a; // expected-error {{include <experimental/coroutine>}}
-  // expected-error@-1 {{use of undeclared identifier 'a'}}
-}
-
-void no_coroutine_traits_bad_arg_yield() {
-  co_yield a; // expected-error {{include <experimental/coroutine>}}
-  // expected-error@-1 {{use of undeclared identifier 'a'}}
-}
-
-void no_coroutine_traits_bad_arg_return() {
-  co_return a; // expected-error {{include <experimental/coroutine>}}
-  // expected-error@-1 {{use of undeclared identifier 'a'}}
-}
-
-void no_coroutine_traits() {
-  co_await 4; // expected-error {{std::coroutine_traits type was not found; include <coroutine> before defining a coroutine; include <experimental/coroutine> if your version of libcxx is less than 14.0}}
-}
-
-namespace std {
-namespace experimental {
-
-template <class... Args>
-struct void_t_imp {
-  using type = void;
-};
-template <class... Args>
-using void_t = typename void_t_imp<Args...>::type;
-
-template <class T, class = void>
-struct traits_sfinae_base {};
-
-template <class T>
-struct traits_sfinae_base<T, void_t<typename T::promise_type>> {
-  using promise_type = typename T::promise_type;
-};
-
-template <class Ret, class... Args>
-struct coroutine_traits : public traits_sfinae_base<Ret> {};
-} // namespace experimental
-} // namespace std
-
-template <typename Promise> struct coro {};
-template <typename Promise, typename... Ps>
-struct std::experimental::coroutine_traits<coro<Promise>, Ps...> {
-  using promise_type = Promise;
-};
-
-struct awaitable {
-  bool await_ready() noexcept;
-  template <typename F>
-  void await_suspend(F) noexcept;
-  void await_resume() noexcept;
-} a;
-
-struct suspend_always {
-  bool await_ready() noexcept { return false; }
-  template <typename F>
-  void await_suspend(F) noexcept;
-  void await_resume() noexcept {}
-};
-
-struct suspend_never {
-  bool await_ready() noexcept { return true; }
-  template <typename F>
-  void await_suspend(F) noexcept;
-  void await_resume() noexcept {}
-};
-
-struct auto_await_suspend {
-  bool await_ready();
-  template <typename F> auto await_suspend(F) {}
-  void await_resume();
-};
-
-struct DummyVoidTag {};
-DummyVoidTag no_specialization() { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<DummyVoidTag>' has no member named 'promise_type'}}
-  co_await a;                      // expected-warning {{coroutine_traits defined in std::experimental namespace is deprecated. Consider updating libcxx and include <coroutine> instead of <experimental/coroutine>}}
-}
-
-template <typename... T>
-struct std::experimental::coroutine_traits<int, T...> {};
-
-int no_promise_type() { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<int>' has no member named 'promise_type'}}
-  co_await a;
-}
-
-int no_promise_type_multiple_awaits(int) { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<int, int>' has no member named 'promise_type'}}
-  co_await a;
-  co_await a;
-}
-
-template <>
-struct std::experimental::coroutine_traits<double, double> { typedef int promise_type; };
-double bad_promise_type(double) { // expected-error {{this function cannot be a coroutine: 'experimental::coroutine_traits<double, double>::promise_type' (aka 'int') is not a class}}
-  co_await a;
-}
-
-template <>
-struct std::experimental::coroutine_traits<double, int> {
-  struct promise_type {};
-};
-double bad_promise_type_2(int) { // expected-error {{no member named 'initial_suspend'}}
-  co_yield 0;                    // expected-error {{no member named 'yield_value' in 'std::experimental::coroutine_traits<double, int>::promise_type'}}
-}
-
-struct promise; // expected-note {{forward declaration}}
-struct promise_void;
-struct void_tag {};
-template <typename... T>
-struct std::experimental::coroutine_traits<void, T...> { using promise_type = promise; };
-template <typename... T>
-struct std::experimental::coroutine_traits<void, void_tag, T...> { using promise_type = promise_void; };
-
-// FIXME: This diagnostic is terrible.
-void undefined_promise() { // expected-error {{this function cannot be a coroutine: 'experimental::coroutine_traits<void>::promise_type' (aka 'promise') is an incomplete type}}
-  co_await a;
-}
-
-struct yielded_thing {
-  const char *p;
-  short a, b;
-};
-
-struct not_awaitable {};
-
-struct promise {
-  void get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  awaitable yield_value(int);           // expected-note 2{{candidate}}
-  awaitable yield_value(yielded_thing); // expected-note 2{{candidate}}
-  not_awaitable yield_value(void());    // expected-note 2{{candidate}}
-  void return_value(int);               // expected-note 2{{here}}
-  void unhandled_exception();
-};
-
-struct promise_void {
-  void get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-
-void no_coroutine_handle() { // expected-error {{std::coroutine_handle type was not found; include <coroutine> before defining a coroutine; include <experimental/coroutine> if your version of libcxx is less than 14.0}}
-  //expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
-  co_return 5; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-namespace std {
-namespace experimental {
-template <class PromiseType = void>
-struct coroutine_handle {
-  static coroutine_handle from_address(void *) noexcept;
-};
-template <>
-struct coroutine_handle<void> {
-  template <class PromiseType>
-  coroutine_handle(coroutine_handle<PromiseType>) noexcept;
-  static coroutine_handle from_address(void *) noexcept;
-};
-} // namespace experimental
-} // namespace std
-
-void yield() {
-  co_yield 0;
-  co_yield {"foo", 1, 2};
-  co_yield {1e100};                    // expected-error {{cannot be narrowed}} expected-note {{explicit cast}} expected-warning {{implicit conversion}} expected-warning {{braces around scalar}}
-  co_yield {"foo", __LONG_LONG_MAX__}; // expected-error {{cannot be narrowed}} expected-note {{explicit cast}} expected-warning {{changes value}}
-  co_yield {"foo"};
-  co_yield "foo"; // expected-error {{no matching}}
-  co_yield 1.0;
-  co_yield yield; // expected-error {{no member named 'await_ready' in 'not_awaitable'}}
-}
-
-void check_auto_await_suspend() {
-  co_await auto_await_suspend{}; // Should compile successfully.
-}
-
-void coreturn(int n) {
-  co_await a;
-  if (n == 0)
-    co_return 3;
-  if (n == 1)
-    co_return {4}; // expected-warning {{braces around scalar initializer}}
-  if (n == 2)
-    co_return "foo"; // expected-error {{cannot initialize a parameter of type 'int' with an lvalue of type 'const char [4]'}}
-  co_return 42;
-}
-
-template <class T>
-void co_await_non_dependent_arg(T) {
-  co_await a;
-}
-template void co_await_non_dependent_arg(int);
-
-void mixed_yield() {
-  co_yield 0; // expected-note {{use of 'co_yield'}}
-  return;     // expected-error {{not allowed in coroutine}}
-}
-
-void mixed_yield_invalid() {
-  co_yield blah; // expected-error {{use of undeclared identifier}}
-  // expected-note@-1 {{function is a coroutine due to use of 'co_yield'}}
-  return; // expected-error {{return statement not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_yield_template(T) {
-  co_yield blah; // expected-error {{use of undeclared identifier}}
-  // expected-note@-1 {{function is a coroutine due to use of 'co_yield'}}
-  return; // expected-error {{return statement not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_yield_template2(T) {
-  co_yield 42;
-  // expected-note@-1 {{function is a coroutine due to use of 'co_yield'}}
-  return; // expected-error {{return statement not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_yield_template3(T v) {
-  co_yield blah(v);
-  // expected-note@-1 {{function is a coroutine due to use of 'co_yield'}}
-  return; // expected-error {{return statement not allowed in coroutine}}
-}
-
-void mixed_await() {
-  co_await a; // expected-note {{use of 'co_await'}}
-  return;     // expected-error {{not allowed in coroutine}}
-}
-
-void mixed_await_invalid() {
-  co_await 42; // expected-error {{'int' is not a structure or union}}
-  // expected-note@-1 {{function is a coroutine due to use of 'co_await'}}
-  return; // expected-error {{not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_await_template(T) {
-  co_await 42;
-  // expected-note@-1 {{function is a coroutine due to use of 'co_await'}}
-  return; // expected-error {{not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_await_template2(T v) {
-  co_await v; // expected-error {{'long' is not a structure or union}}
-  // expected-note@-1 {{function is a coroutine due to use of 'co_await'}}
-  return; // expected-error {{not allowed in coroutine}}
-}
-template void mixed_await_template2(long); // expected-note {{requested here}}
-
-void only_coreturn(void_tag) {
-  co_return; // OK
-}
-
-void mixed_coreturn(void_tag, bool b) {
-  if (b)
-    co_return; // expected-note {{use of 'co_return'}}
-  else
-    return; // expected-error {{not allowed in coroutine}}
-}
-
-void mixed_coreturn_invalid(bool b) {
-  if (b)
-    co_return; // expected-note {{use of 'co_return'}}
-  // expected-error@-1 {{no member named 'return_void' in 'promise'}}
-  else
-    return; // expected-error {{not allowed in coroutine}}
-}
-
-template <class T>
-void mixed_coreturn_template(void_tag, bool b, T v) {
-  if (b)
-    co_return v; // expected-note {{use of 'co_return'}}
-  // expected-error@-1 {{no member named 'return_value' in 'promise_void'}}
-  else
-    return; // expected-error {{not allowed in coroutine}}
-}
-template void mixed_coreturn_template(void_tag, bool, int); // expected-note {{requested here}}
-
-template <class T>
-void mixed_coreturn_template2(bool b, T) {
-  if (b)
-    co_return v; // expected-note {{use of 'co_return'}}
-  // expected-error@-1 {{use of undeclared identifier 'v'}}
-  else
-    return; // expected-error {{not allowed in coroutine}}
-}
-
-struct CtorDtor {
-  CtorDtor() {
-    co_yield 0; // expected-error {{'co_yield' cannot be used in a constructor}}
-  }
-  CtorDtor(awaitable a) {
-    // The spec doesn't say this is ill-formed, but it must be.
-    co_await a; // expected-error {{'co_await' cannot be used in a constructor}}
-  }
-  ~CtorDtor() {
-    co_return 0; // expected-error {{'co_return' cannot be used in a destructor}}
-  }
-  void operator=(CtorDtor &) {
-    co_yield 0; // OK.
-  }
-  void operator=(CtorDtor const &) {
-    co_yield 0; // OK.
-  }
-  void operator=(CtorDtor &&) {
-    co_await a; // OK.
-  }
-  void operator=(CtorDtor const &&) {
-    co_await a; // OK.
-  }
-  void operator=(int) {
-    co_await a; // OK. Not a special member
-  }
-};
-
-namespace std {
-class type_info;
-}
-
-void unevaluated() {
-  decltype(co_await a); // expected-error {{'co_await' cannot be used in an unevaluated context}}
-                        // expected-warning@-1 {{declaration does not declare anything}}
-  sizeof(co_await a);   // expected-error {{'co_await' cannot be used in an unevaluated context}}
-                        // expected-error@-1 {{invalid application of 'sizeof' to an incomplete type 'void'}}
-                        // expected-warning@-2 {{expression with side effects has no effect in an unevaluated context}}
-  typeid(co_await a);   // expected-error {{'co_await' cannot be used in an unevaluated context}}
-                        // expected-warning@-1 {{expression with side effects has no effect in an unevaluated context}}
-                        // expected-warning@-2 {{expression result unused}}
-  decltype(co_yield 1); // expected-error {{'co_yield' cannot be used in an unevaluated context}}
-                        // expected-warning@-1 {{declaration does not declare anything}}
-  sizeof(co_yield 2);   // expected-error {{'co_yield' cannot be used in an unevaluated context}}
-                        // expected-error@-1 {{invalid application of 'sizeof' to an incomplete type 'void'}}
-                        // expected-warning@-2 {{expression with side effects has no effect in an unevaluated context}}
-  typeid(co_yield 3);   // expected-error {{'co_yield' cannot be used in an unevaluated context}}
-                        // expected-warning@-1 {{expression with side effects has no effect in an unevaluated context}}
-                        // expected-warning@-2 {{expression result unused}}
-}
-
-// [expr.await]p2: "An await-expression shall not appear in a default argument."
-// FIXME: A better diagnostic would explicitly state that default arguments are
-// not allowed. A user may not understand that this is "outside a function."
-void default_argument(int arg = co_await 0) {} // expected-error {{'co_await' cannot be used outside a function}}
-
-void await_in_catch_coroutine() {
-  try {
-  } catch (...) {                   // FIXME: Emit a note diagnostic pointing out the try handler on this line.
-    []() -> void { co_await a; }(); // OK
-    co_await a;                     // expected-error {{'co_await' cannot be used in the handler of a try block}}
-  }
-}
-
-void await_nested_in_catch_coroutine() {
-  try {
-  } catch (...) { // FIXME: Emit a note diagnostic pointing out the try handler on this line.
-    try {
-      co_await a;                     // expected-error {{'co_await' cannot be used in the handler of a try block}}
-      []() -> void { co_await a; }(); // OK
-    } catch (...) {
-      co_return 123;
-    }
-  }
-}
-
-void await_in_lambda_in_catch_coroutine() {
-  try {
-  } catch (...) {
-    []() -> void { co_await a; }(); // OK
-  }
-}
-
-void yield_in_catch_coroutine() {
-  try {
-  } catch (...) {
-    co_yield 1; // expected-error {{'co_yield' cannot be used in the handler of a try block}}
-  }
-}
-
-void return_in_catch_coroutine() {
-  try {
-  } catch (...) {
-    co_return 123; // OK
-  }
-}
-
-constexpr auto constexpr_deduced_return_coroutine() {
-  co_yield 0; // expected-error {{'co_yield' cannot be used in a constexpr function}}
-  // expected-error@-1 {{'co_yield' cannot be used in a function with a deduced return type}}
-}
-
-void varargs_coroutine(const char *, ...) {
-  co_await a; // expected-error {{'co_await' cannot be used in a varargs function}}
-}
-
-auto deduced_return_coroutine() {
-  co_await a; // expected-error {{'co_await' cannot be used in a function with a deduced return type}}
-}
-
-struct outer {};
-struct await_arg_1 {};
-struct await_arg_2 {};
-
-namespace adl_ns {
-struct coawait_arg_type {};
-awaitable operator co_await(coawait_arg_type) noexcept;
-} // namespace adl_ns
-
-namespace dependent_operator_co_await_lookup {
-template <typename T> void await_template(T t) {
-  // no unqualified lookup results
-  co_await t; // expected-error {{no member named 'await_ready' in 'dependent_operator_co_await_lookup::not_awaitable'}}
-  // expected-error@-1 {{call to function 'operator co_await' that is neither visible in the template definition nor found by argument-dependent lookup}}
-};
-template void await_template(awaitable);
-
-struct indirectly_awaitable {
-  indirectly_awaitable(outer);
-};
-awaitable operator co_await(indirectly_awaitable); // expected-note {{should be declared prior to}}
-template void await_template(indirectly_awaitable);
-
-struct not_awaitable {};
-template void await_template(not_awaitable); // expected-note {{instantiation}}
-
-template <typename T> void await_template_2(T t) {
-  // one unqualified lookup result
-  co_await t;
-};
-template void await_template(outer); // expected-note {{instantiation}}
-template void await_template_2(outer);
-
-struct transform_awaitable {};
-struct transformed {};
-
-struct transform_promise {
-  typedef transform_awaitable await_arg;
-  coro<transform_promise> get_return_object();
-  transformed initial_suspend();
-  ::adl_ns::coawait_arg_type final_suspend() noexcept;
-  transformed await_transform(transform_awaitable);
-  void unhandled_exception();
-  void return_void();
-};
-template <class AwaitArg>
-struct basic_promise {
-  typedef AwaitArg await_arg;
-  coro<basic_promise> get_return_object();
-  awaitable initial_suspend();
-  awaitable final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-};
-
-awaitable operator co_await(await_arg_1);
-
-template <typename T, typename U>
-coro<T> await_template_3(U t) {
-  co_await t;
-}
-
-template coro<basic_promise<await_arg_1>> await_template_3<basic_promise<await_arg_1>>(await_arg_1);
-
-template <class T, int I = 0>
-struct dependent_member {
-  coro<T> mem_fn() const {
-    co_await typename T::await_arg{}; // expected-error {{call to function 'operator co_await'}}}
-  }
-  template <class U>
-  coro<T> dep_mem_fn(U t) {
-    co_await t;
-  }
-};
-
-template <>
-struct dependent_member<long> {
-  // FIXME this diagnostic is terrible
-  coro<transform_promise> mem_fn() const { // expected-error {{no member named 'await_ready' in 'dependent_operator_co_await_lookup::transformed'}}
-    // expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
-    // expected-note@+1 {{function is a coroutine due to use of 'co_await' here}}
-    co_await transform_awaitable{};
-    // expected-error@-1 {{no member named 'await_ready'}}
-  }
-  template <class R, class U>
-  coro<R> dep_mem_fn(U u) { co_await u; }
-};
-
-awaitable operator co_await(await_arg_2); // expected-note {{'operator co_await' should be declared prior to the call site}}
-
-template struct dependent_member<basic_promise<await_arg_1>, 0>;
-template struct dependent_member<basic_promise<await_arg_2>, 0>; // expected-note {{in instantiation}}
-
-template <>
-coro<transform_promise>
-// FIXME this diagnostic is terrible
-dependent_member<long>::dep_mem_fn<transform_promise>(int) { // expected-error {{no member named 'await_ready' in 'dependent_operator_co_await_lookup::transformed'}}
-  //expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
-  //expected-note@+1 {{function is a coroutine due to use of 'co_await' here}}
-  co_await transform_awaitable{};
-  // expected-error@-1 {{no member named 'await_ready'}}
-}
-
-void operator co_await(transform_awaitable) = delete;
-awaitable operator co_await(transformed);
-
-template coro<transform_promise>
-    dependent_member<long>::dep_mem_fn<transform_promise>(transform_awaitable);
-
-template <>
-coro<transform_promise> dependent_member<long>::dep_mem_fn<transform_promise>(long) {
-  co_await transform_awaitable{};
-}
-
-template <>
-struct dependent_member<int> {
-  coro<transform_promise> mem_fn() const {
-    co_await transform_awaitable{};
-  }
-};
-
-template coro<transform_promise> await_template_3<transform_promise>(transform_awaitable);
-template struct dependent_member<transform_promise>;
-template coro<transform_promise> dependent_member<transform_promise>::dep_mem_fn(transform_awaitable);
-} // namespace dependent_operator_co_await_lookup
-
-struct yield_fn_tag {};
-template <>
-struct std::experimental::coroutine_traits<void, yield_fn_tag> {
-  struct promise_type {
-    // FIXME: add an await_transform overload for functions
-    awaitable yield_value(int());
-    void return_value(int());
-
-    suspend_never initial_suspend();
-    suspend_never final_suspend() noexcept;
-    void get_return_object();
-    void unhandled_exception();
-  };
-};
-
-namespace placeholder {
-awaitable f(), f(int); // expected-note 4{{possible target}}
-int g(), g(int);       // expected-note 2{{candidate}}
-void x() {
-  co_await f; // expected-error {{reference to overloaded function}}
-}
-void y() {
-  co_yield g; // expected-error {{no matching member function for call to 'yield_value'}}
-}
-void z() {
-  co_await a;
-  co_return g; // expected-error {{address of overloaded function 'g' does not match required type 'int'}}
-}
-
-void x(yield_fn_tag) {
-  co_await f; // expected-error {{reference to overloaded function}}
-}
-void y(yield_fn_tag) {
-  co_yield g;
-}
-void z(yield_fn_tag) {
-  co_await a;
-  co_return g;
-}
-} // namespace placeholder
-
-struct bad_promise_1 {
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-};
-coro<bad_promise_1> missing_get_return_object() { // expected-error {{no member named 'get_return_object' in 'bad_promise_1'}}
-  co_await a;
-}
-
-struct bad_promise_2 {
-  coro<bad_promise_2> get_return_object();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-};
-// FIXME: This shouldn't happen twice
-coro<bad_promise_2> missing_initial_suspend() { // expected-error {{no member named 'initial_suspend' in 'bad_promise_2'}}
-  co_await a;
-}
-
-struct bad_promise_3 {
-  coro<bad_promise_3> get_return_object();
-  suspend_always initial_suspend();
-  void unhandled_exception();
-  void return_void();
-};
-coro<bad_promise_3> missing_final_suspend() noexcept { // expected-error {{no member named 'final_suspend' in 'bad_promise_3'}}
-  co_await a;
-}
-
-struct bad_promise_4 {
-  coro<bad_promise_4> get_return_object();
-  not_awaitable initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-};
-// FIXME: This diagnostic is terrible.
-coro<bad_promise_4> bad_initial_suspend() { // expected-error {{no member named 'await_ready' in 'not_awaitable'}}
-  // expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
-  co_await a; // expected-note {{function is a coroutine due to use of 'co_await' here}}
-}
-
-struct bad_promise_5 {
-  coro<bad_promise_5> get_return_object();
-  suspend_always initial_suspend();
-  not_awaitable final_suspend() noexcept;
-  void return_void();
-};
-// FIXME: This diagnostic is terrible.
-coro<bad_promise_5> bad_final_suspend() { // expected-error {{no member named 'await_ready' in 'not_awaitable'}}
-  // expected-note@-1 {{call to 'final_suspend' implicitly required by the final suspend point}}
-  co_await a; // expected-note {{function is a coroutine due to use of 'co_await' here}}
-}
-
-struct bad_promise_6 {
-  coro<bad_promise_6> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();           // expected-note 2 {{member 'return_void' first declared here}}
-  void return_value(int) const; // expected-note 2 {{member 'return_value' first declared here}}
-  void return_value(int);
-};
-coro<bad_promise_6> bad_implicit_return() { // expected-error {{'bad_promise_6' declares both 'return_value' and 'return_void'}}
-  co_await a;
-}
-
-template <class T>
-coro<T> bad_implicit_return_dependent(T) { // expected-error {{'bad_promise_6' declares both 'return_value' and 'return_void'}}
-  co_await a;
-}
-template coro<bad_promise_6> bad_implicit_return_dependent(bad_promise_6); // expected-note {{in instantiation}}
-
-struct bad_promise_7 { // expected-note 2 {{defined here}}
-  coro<bad_promise_7> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-};
-coro<bad_promise_7> no_unhandled_exception() { // expected-error {{'bad_promise_7' is required to declare the member 'unhandled_exception()'}}
-  co_await a;
-}
-
-template <class T>
-coro<T> no_unhandled_exception_dependent(T) { // expected-error {{'bad_promise_7' is required to declare the member 'unhandled_exception()'}}
-  co_await a;
-}
-template coro<bad_promise_7> no_unhandled_exception_dependent(bad_promise_7); // expected-note {{in instantiation}}
-
-struct bad_promise_base {
-private:
-  void return_void(); // expected-note 2 {{declared private here}}
-};
-struct bad_promise_8 : bad_promise_base {
-  coro<bad_promise_8> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception() __attribute__((unavailable)); // expected-note 2 {{marked unavailable here}}
-  void unhandled_exception() const;
-  void unhandled_exception(void *) const;
-};
-coro<bad_promise_8> calls_unhandled_exception() {
-  // expected-error@-1 {{'unhandled_exception' is unavailable}}
-  // expected-error@-2 {{'return_void' is a private member}}
-  co_await a;
-}
-
-template <class T>
-coro<T> calls_unhandled_exception_dependent(T) {
-  // expected-error@-1 {{'unhandled_exception' is unavailable}}
-  // expected-error@-2 {{'return_void' is a private member}}
-  co_await a;
-}
-template coro<bad_promise_8> calls_unhandled_exception_dependent(bad_promise_8); // expected-note {{in instantiation}}
-
-struct bad_promise_9 {
-  coro<bad_promise_9> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void await_transform(void *);
-  awaitable await_transform(int) __attribute__((unavailable)); // expected-note {{explicitly marked unavailable}}
-  void return_void();
-  void unhandled_exception();
-};
-coro<bad_promise_9> calls_await_transform() {
-  co_await 42; // expected-error {{'await_transform' is unavailable}}
-}
-
-struct bad_promise_10 {
-  coro<bad_promise_10> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  int await_transform;
-  void return_void();
-  void unhandled_exception();
-};
-coro<bad_promise_10> bad_coawait() {
-  // FIXME this diagnostic is terrible
-  co_await 42; // expected-error {{called object type 'int' is not a function or function pointer}}
-  // expected-note@-1 {{call to 'await_transform' implicitly required by 'co_await' here}}
-}
-
-struct call_operator {
-  template <class... Args>
-  awaitable operator()(Args...) const { return a; }
-};
-void ret_void();
-struct good_promise_1 {
-  coro<good_promise_1> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  static const call_operator await_transform;
-  using Fn = void (*)();
-  Fn return_void = ret_void;
-};
-const call_operator good_promise_1::await_transform;
-coro<good_promise_1> ok_static_coawait() {
-  // FIXME this diagnostic is terrible
-  co_await 42;
-}
-
-template <typename T> void ok_generic_lambda_coawait_PR41909() {
-  [](auto &arg) -> coro<good_promise_1> { // expected-warning {{expression result unused}}
-    co_await 12;
-  };
-  [](auto &arg) -> coro<good_promise_1> {
-    co_await 24;
-  }("argument");
-  [](auto &arg) -> coro<good_promise_1> { // expected-warning {{expression result unused}}
-    []() -> coro<good_promise_1> {
-      co_await 36;
-    };
-    co_await 48;
-  };
-}
-template void ok_generic_lambda_coawait_PR41909<int>(); // expected-note {{in instantiation of function template specialization 'ok_generic_lambda_coawait_PR41909<int>' requested here}}
-
-template <> struct std::experimental::coroutine_traits<int, int, const char **> { using promise_type = promise; };
-
-int main(int, const char **) {
-  co_await a; // expected-error {{'co_await' cannot be used in the 'main' function}}
-}
-
-struct good_promise_2 {
-  float get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-template <> struct std::experimental::coroutine_handle<good_promise_2> {};
-
-template <> struct std::experimental::coroutine_traits<float> { using promise_type = good_promise_2; };
-
-float badly_specialized_coro_handle() { // expected-error {{std::coroutine_handle missing a member named 'from_address'}}
-  //expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-namespace std {
-struct nothrow_t {};
-constexpr nothrow_t nothrow = {};
-} // namespace std
-
-using SizeT = decltype(sizeof(int));
-
-void *operator new(SizeT __sz, const std::nothrow_t &) noexcept;
-void operator delete(void *__p, const std::nothrow_t &)noexcept;
-
-struct promise_on_alloc_failure_tag {};
-
-template <>
-struct std::experimental::coroutine_traits<int, promise_on_alloc_failure_tag> {
-  struct promise_type {
-    int get_return_object() {}
-    suspend_always initial_suspend() { return {}; }
-    suspend_always final_suspend() noexcept { return {}; }
-    void return_void() {}
-    int get_return_object_on_allocation_failure(); // expected-error{{'promise_type': 'get_return_object_on_allocation_failure()' must be a static member function}}
-    void unhandled_exception();
-  };
-};
-
-extern "C" int f(promise_on_alloc_failure_tag) {
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-struct bad_promise_11 {
-  coro<bad_promise_11> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-
-private:
-  static coro<bad_promise_11> get_return_object_on_allocation_failure(); // expected-note 2 {{declared private here}}
-};
-coro<bad_promise_11> private_alloc_failure_handler() {
-  // expected-error@-1 {{'get_return_object_on_allocation_failure' is a private member of 'bad_promise_11'}}
-  co_return; // FIXME: Add a "declared coroutine here" note.
-}
-
-template <class T>
-coro<T> dependent_private_alloc_failure_handler(T) {
-  // expected-error@-1 {{'get_return_object_on_allocation_failure' is a private member of 'bad_promise_11'}}
-  co_return; // FIXME: Add a "declared coroutine here" note.
-}
-template coro<bad_promise_11> dependent_private_alloc_failure_handler(bad_promise_11);
-// expected-note@-1 {{requested here}}
-
-struct bad_promise_12 {
-  coro<bad_promise_12> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-  static coro<bad_promise_12> get_return_object_on_allocation_failure();
-
-  static void *operator new(SizeT);
-  // expected-error@-1 2 {{'operator new' is required to have a non-throwing noexcept specification when the promise type declares 'get_return_object_on_allocation_failure()'}}
-};
-coro<bad_promise_12> throwing_in_class_new() { // expected-note {{call to 'operator new' implicitly required by coroutine function here}}
-  co_return;
-}
-
-template <class T>
-coro<T> dependent_throwing_in_class_new(T) { // expected-note {{call to 'operator new' implicitly required by coroutine function here}}
-  co_return;
-}
-template coro<bad_promise_12> dependent_throwing_in_class_new(bad_promise_12); // expected-note {{requested here}}
-
-struct good_promise_13 {
-  coro<good_promise_13> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-  void return_void();
-  static coro<good_promise_13> get_return_object_on_allocation_failure();
-};
-coro<good_promise_13> uses_nothrow_new() {
-  co_return;
-}
-
-template <class T>
-coro<T> dependent_uses_nothrow_new(T) {
-  co_return;
-}
-template coro<good_promise_13> dependent_uses_nothrow_new(good_promise_13);
-
-struct good_promise_custom_new_operator {
-  coro<good_promise_custom_new_operator> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-  void *operator new(SizeT, double, float, int);
-};
-
-coro<good_promise_custom_new_operator>
-good_coroutine_calls_custom_new_operator(double, float, int) {
-  co_return;
-}
-
-struct coroutine_nonstatic_member_struct;
-
-struct good_promise_nonstatic_member_custom_new_operator {
-  coro<good_promise_nonstatic_member_custom_new_operator> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-  void *operator new(SizeT, coroutine_nonstatic_member_struct &, double);
-};
-
-struct good_promise_noexcept_custom_new_operator {
-  static coro<good_promise_noexcept_custom_new_operator> get_return_object_on_allocation_failure();
-  coro<good_promise_noexcept_custom_new_operator> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-  void *operator new(SizeT, double, float, int) noexcept;
-};
-
-coro<good_promise_noexcept_custom_new_operator>
-good_coroutine_calls_noexcept_custom_new_operator(double, float, int) {
-  co_return;
-}
-
-struct mismatch_gro_type_tag1 {};
-template <>
-struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag1> {
-  struct promise_type {
-    void get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
-    suspend_always initial_suspend() { return {}; }
-    suspend_always final_suspend() noexcept { return {}; }
-    void return_void() {}
-    void unhandled_exception();
-  };
-};
-
-extern "C" int f(mismatch_gro_type_tag1) {
-  // expected-error@-1 {{cannot initialize return object of type 'int' with an rvalue of type 'void'}}
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-struct mismatch_gro_type_tag2 {};
-template <>
-struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag2> {
-  struct promise_type {
-    void *get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
-    suspend_always initial_suspend() { return {}; }
-    suspend_always final_suspend() noexcept { return {}; }
-    void return_void() {}
-    void unhandled_exception();
-  };
-};
-
-extern "C" int f(mismatch_gro_type_tag2) {
-  // cxx2b-error@-1 {{cannot initialize return object of type 'int' with an rvalue of type 'void *'}}
-  // cxx14_20-error@-2 {{cannot initialize return object of type 'int' with an lvalue of type 'void *'}}
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-struct mismatch_gro_type_tag3 {};
-template <>
-struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag3> {
-  struct promise_type {
-    int get_return_object() {}
-    static void get_return_object_on_allocation_failure() {} //expected-note {{member 'get_return_object_on_allocation_failure' declared here}}
-    suspend_always initial_suspend() { return {}; }
-    suspend_always final_suspend() noexcept { return {}; }
-    void return_void() {}
-    void unhandled_exception();
-  };
-};
-
-extern "C" int f(mismatch_gro_type_tag3) {
-  // expected-error@-1 {{cannot initialize return object of type 'int' with an rvalue of type 'void'}}
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-struct mismatch_gro_type_tag4 {};
-template <>
-struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag4> {
-  struct promise_type {
-    int get_return_object() {}
-    static char *get_return_object_on_allocation_failure() {} //expected-note {{member 'get_return_object_on_allocation_failure' declared}}
-    suspend_always initial_suspend() { return {}; }
-    suspend_always final_suspend() noexcept { return {}; }
-    void return_void() {}
-    void unhandled_exception();
-  };
-};
-
-extern "C" int f(mismatch_gro_type_tag4) {
-  // expected-error@-1 {{cannot initialize return object of type 'int' with an rvalue of type 'char *'}}
-  co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
-}
-
-struct bad_promise_no_return_func { // expected-note {{'bad_promise_no_return_func' defined here}}
-  coro<bad_promise_no_return_func> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void unhandled_exception();
-};
-// FIXME: The PDTS currently specifies this as UB, technically forbidding a
-// diagnostic.
-coro<bad_promise_no_return_func> no_return_value_or_return_void() {
-  // expected-error@-1 {{'bad_promise_no_return_func' must declare either 'return_value' or 'return_void'}}
-  co_await a;
-}
-
-struct bad_await_suspend_return {
-  bool await_ready();
-  // expected-error@+1 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'char')}}
-  char await_suspend(std::experimental::coroutine_handle<>);
-  void await_resume();
-};
-struct bad_await_ready_return {
-  // expected-note@+1 {{return type of 'await_ready' is required to be contextually convertible to 'bool'}}
-  void await_ready();
-  bool await_suspend(std::experimental::coroutine_handle<>);
-  void await_resume();
-};
-struct await_ready_explicit_bool {
-  struct BoolT {
-    explicit operator bool() const;
-  };
-  BoolT await_ready();
-  void await_suspend(std::experimental::coroutine_handle<>);
-  void await_resume();
-};
-template <class SuspendTy>
-struct await_suspend_type_test {
-  bool await_ready();
-  // expected-error@+2 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'bool &')}}
-  // expected-error@+1 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'bool &&')}}
-  SuspendTy await_suspend(std::experimental::coroutine_handle<>);
-  // cxx20_2b-warning@-1 {{volatile-qualified return type 'const volatile bool' is deprecated}}
-  void await_resume();
-};
-void test_bad_suspend() {
-  {
-    // FIXME: The actual error emitted here is terrible, and no number of notes can save it.
-    bad_await_ready_return a;
-    // expected-error@+1 {{value of type 'void' is not contextually convertible to 'bool'}}
-    co_await a; // expected-note {{call to 'await_ready' implicitly required by coroutine function here}}
-  }
-  {
-    bad_await_suspend_return b;
-    co_await b; // expected-note {{call to 'await_suspend' implicitly required by coroutine function here}}
-  }
-  {
-    await_ready_explicit_bool c;
-    co_await c; // OK
-  }
-  {
-    await_suspend_type_test<bool &&> a;
-    await_suspend_type_test<bool &> b;
-    await_suspend_type_test<const void> c;
-    await_suspend_type_test<const volatile bool> d; // cxx20_2b-note {{in instantiation of template class}}
-    co_await a;                                     // expected-note {{call to 'await_suspend' implicitly required by coroutine function here}}
-    co_await b;                                     // expected-note {{call to 'await_suspend' implicitly required by coroutine function here}}
-    co_await c;                                     // OK
-    co_await d;                                     // OK
-  }
-}
-
-template <int ID = 0>
-struct NoCopy {
-  NoCopy(NoCopy const &) = delete; // expected-note 2 {{deleted here}}
-};
-template <class T, class U>
-void test_dependent_param(T t, U) {
-  // expected-error@-1 {{call to deleted constructor of 'NoCopy<0>'}}
-  // expected-error@-2 {{call to deleted constructor of 'NoCopy<1>'}}
-  ((void)t);
-  co_return 42;
-}
-template void test_dependent_param(NoCopy<0>, NoCopy<1>); // expected-note {{requested here}}
-
-namespace CoroHandleMemberFunctionTest {
-struct CoroMemberTag {};
-struct BadCoroMemberTag {};
-
-template <class T, class U>
-constexpr bool IsSameV = false;
-template <class T>
-constexpr bool IsSameV<T, T> = true;
-
-template <class T>
-struct TypeTest {
-  template <class U>
-  static constexpr bool IsSame = IsSameV<T, U>;
-
-  template <class... Args>
-  static constexpr bool MatchesArgs = IsSameV<T,
-                                              std::experimental::coroutine_traits<CoroMemberTag, Args...>>;
-};
-
-template <class T>
-struct AwaitReturnsType {
-  bool await_ready() const;
-  void await_suspend(...) const;
-  T await_resume() const;
-};
-
-template <class... CoroTraitsArgs>
-struct CoroMemberPromise {
-  using TraitsT = std::experimental::coroutine_traits<CoroTraitsArgs...>;
-  using TypeTestT = TypeTest<TraitsT>;
-  using AwaitTestT = AwaitReturnsType<TypeTestT>;
-
-  CoroMemberTag get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-
-  AwaitTestT yield_value(int);
-
-  void return_void();
-  void unhandled_exception();
-};
-
-} // namespace CoroHandleMemberFunctionTest
-
-template <class... Args>
-struct ::std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::CoroMemberTag, Args...> {
-  using promise_type = CoroHandleMemberFunctionTest::CoroMemberPromise<CoroHandleMemberFunctionTest::CoroMemberTag, Args...>;
-};
-
-namespace CoroHandleMemberFunctionTest {
-struct TestType {
-
-  CoroMemberTag test_qual() {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType &>, "");
-    static_assert(!TC.MatchesArgs<TestType>, "");
-    static_assert(!TC.MatchesArgs<TestType *>, "");
-  }
-
-  CoroMemberTag test_sanity(int *) const {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<const TestType &>, ""); // expected-error {{static_assert failed}}
-    static_assert(TC.MatchesArgs<const TestType &>, ""); // expected-error {{static_assert failed}}
-    static_assert(TC.MatchesArgs<const TestType &, int *>, "");
-  }
-
-  CoroMemberTag test_qual(int *, const float &&, volatile void *volatile) const {
-    // cxx20_2b-warning@-1 {{volatile-qualified parameter type}}
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<const TestType &, int *, const float &&, volatile void *volatile>, "");
-  }
-
-  CoroMemberTag test_qual() const volatile {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<const volatile TestType &>, "");
-  }
-
-  CoroMemberTag test_ref_qual() & {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType &>, "");
-  }
-  CoroMemberTag test_ref_qual() const & {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType const &>, "");
-  }
-  CoroMemberTag test_ref_qual() && {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType &&>, "");
-  }
-  CoroMemberTag test_ref_qual(const char *&) const volatile && {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType const volatile &&, const char *&>, "");
-  }
-
-  CoroMemberTag test_args(int) {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType &, int>, "");
-  }
-  CoroMemberTag test_args(int, long &, void *) const {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<TestType const &, int, long &, void *>, "");
-  }
-
-  template <class... Args>
-  CoroMemberTag test_member_template(Args...) const && {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<TestType const &&, Args...>, "");
-  }
-
-  static CoroMemberTag test_static() {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<>, "");
-    static_assert(!TC.MatchesArgs<TestType>, "");
-    static_assert(!TC.MatchesArgs<TestType &>, "");
-    static_assert(!TC.MatchesArgs<TestType *>, "");
-  }
-
-  static CoroMemberTag test_static(volatile void *const, char &&) {
-    auto TC = co_yield 0;
-    static_assert(TC.MatchesArgs<volatile void *const, char &&>, "");
-  }
-
-  template <class Dummy>
-  static CoroMemberTag test_static_template(const char *volatile &, unsigned) {
-    auto TC = co_yield 0;
-    using TCT = decltype(TC);
-    static_assert(TCT::MatchesArgs<const char *volatile &, unsigned>, "");
-    static_assert(!TCT::MatchesArgs<TestType &, const char *volatile &, unsigned>, "");
-  }
-
-  BadCoroMemberTag test_diagnostics() {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, CoroHandleMemberFunctionTest::TestType &>' has no member named 'promise_type'}}
-    co_return;
-  }
-  BadCoroMemberTag test_diagnostics(int) const && {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, const CoroHandleMemberFunctionTest::TestType &&, int>' has no member named 'promise_type'}}
-    co_return;
-  }
-
-  static BadCoroMemberTag test_static_diagnostics(long *) {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, long *>' has no member named 'promise_type'}}
-    co_return;
-  }
-};
-
-template CoroMemberTag TestType::test_member_template(long, const char *) const &&;
-template CoroMemberTag TestType::test_static_template<void>(const char *volatile &, unsigned);
-
-template <class... Args>
-struct DepTestType {
-
-  CoroMemberTag test_sanity(int *) const {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<const DepTestType &>, ""); // expected-error {{static_assert failed}}
-    static_assert(TC.template MatchesArgs<>, "");                    // expected-error {{static_assert failed}}
-    static_assert(TC.template MatchesArgs<const DepTestType &, int *>, "");
-  }
-
-  CoroMemberTag test_qual() {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType &>, "");
-    static_assert(!TC.template MatchesArgs<DepTestType>, "");
-    static_assert(!TC.template MatchesArgs<DepTestType *>, "");
-  }
-
-  CoroMemberTag test_qual(int *, const float &&, volatile void *volatile) const {
-    // cxx20_2b-warning@-1 {{volatile-qualified parameter type}}
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<const DepTestType &, int *, const float &&, volatile void *volatile>, "");
-  }
-
-  CoroMemberTag test_qual() const volatile {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<const volatile DepTestType &>, "");
-  }
-
-  CoroMemberTag test_ref_qual() & {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType &>, "");
-  }
-  CoroMemberTag test_ref_qual() const & {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType const &>, "");
-  }
-  CoroMemberTag test_ref_qual() && {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType &&>, "");
-  }
-  CoroMemberTag test_ref_qual(const char *&) const volatile && {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType const volatile &&, const char *&>, "");
-  }
-
-  CoroMemberTag test_args(int) {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType &, int>, "");
-  }
-  CoroMemberTag test_args(int, long &, void *) const {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType const &, int, long &, void *>, "");
-  }
-
-  template <class... UArgs>
-  CoroMemberTag test_member_template(UArgs...) const && {
-    auto TC = co_yield 0;
-    static_assert(TC.template MatchesArgs<DepTestType const &&, UArgs...>, "");
-  }
-
-  static CoroMemberTag test_static() {
-    auto TC = co_yield 0;
-    using TCT = decltype(TC);
-    static_assert(TCT::MatchesArgs<>, "");
-    static_assert(!TCT::MatchesArgs<DepTestType>, "");
-    static_assert(!TCT::MatchesArgs<DepTestType &>, "");
-    static_assert(!TCT::MatchesArgs<DepTestType *>, "");
-
-    // Ensure diagnostics are actually being generated here
-    static_assert(TCT::MatchesArgs<int>, ""); // expected-error {{static_assert failed}}
-  }
-
-  static CoroMemberTag test_static(volatile void *const, char &&) {
-    auto TC = co_yield 0;
-    using TCT = decltype(TC);
-    static_assert(TCT::MatchesArgs<volatile void *const, char &&>, "");
-  }
-
-  template <class Dummy>
-  static CoroMemberTag test_static_template(const char *volatile &, unsigned) {
-    auto TC = co_yield 0;
-    using TCT = decltype(TC);
-    static_assert(TCT::MatchesArgs<const char *volatile &, unsigned>, "");
-    static_assert(!TCT::MatchesArgs<DepTestType &, const char *volatile &, unsigned>, "");
-  }
-};
-
-template struct DepTestType<int>; // expected-note {{requested here}}
-template CoroMemberTag DepTestType<int>::test_member_template(long, const char *) const &&;
-
-template CoroMemberTag DepTestType<int>::test_static_template<void>(const char *volatile &, unsigned);
-
-struct bad_promise_deleted_constructor {
-  // expected-note@+1 {{'bad_promise_deleted_constructor' has been explicitly marked deleted here}}
-  bad_promise_deleted_constructor() = delete;
-  coro<bad_promise_deleted_constructor> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-
-coro<bad_promise_deleted_constructor>
-bad_coroutine_calls_deleted_promise_constructor() {
-  // expected-error@-1 {{call to deleted constructor of 'std::experimental::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_deleted_constructor>>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_deleted_constructor')}}
-  co_return;
-}
-
-// Test that, when the promise type has a constructor whose signature matches
-// that of the coroutine function, that constructor is used. If no matching
-// constructor exists, the default constructor is used as a fallback. If no
-// matching constructors exist at all, an error is emitted. This is an
-// experimental feature that will be proposed for the Coroutines TS.
-
-struct good_promise_default_constructor {
-  good_promise_default_constructor(double, float, int);
-  good_promise_default_constructor() = default;
-  coro<good_promise_default_constructor> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-
-coro<good_promise_default_constructor>
-good_coroutine_calls_default_constructor() {
-  co_return;
-}
-
-struct some_class;
-
-struct good_promise_custom_constructor {
-  good_promise_custom_constructor(some_class &, float, int);
-  good_promise_custom_constructor(double, float, int);
-  good_promise_custom_constructor() = delete;
-  coro<good_promise_custom_constructor> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-
-coro<good_promise_custom_constructor>
-good_coroutine_calls_custom_constructor(double, float, int) {
-  co_return;
-}
-
-struct some_class {
-  coro<good_promise_custom_constructor>
-  good_coroutine_calls_custom_constructor(float, int) {
-    co_return;
-  }
-  coro<good_promise_custom_constructor> static good_coroutine_calls_custom_constructor(double, float, int) {
-    co_return;
-  }
-};
-
-struct bad_promise_no_matching_constructor {
-  bad_promise_no_matching_constructor(int, int, int);
-  // expected-note@+1 2 {{'bad_promise_no_matching_constructor' has been explicitly marked deleted here}}
-  bad_promise_no_matching_constructor() = delete;
-  coro<bad_promise_no_matching_constructor> get_return_object();
-  suspend_always initial_suspend();
-  suspend_always final_suspend() noexcept;
-  void return_void();
-  void unhandled_exception();
-};
-
-coro<bad_promise_no_matching_constructor>
-bad_coroutine_calls_with_no_matching_constructor(int, int) {
-  // expected-error@-1 {{call to deleted constructor of 'std::experimental::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor>, int, int>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor')}}
-  co_return;
-}
-
-struct some_class2 {
-  coro<bad_promise_no_matching_constructor>
-  bad_coroutine_calls_with_no_matching_constructor(int, int, int) {
-    // expected-error@-1 {{call to deleted constructor}}
-    co_return;
-  }
-};
-
-} // namespace CoroHandleMemberFunctionTest
-
-class awaitable_no_unused_warn {
-public:
-  using handle_type = std::experimental::coroutine_handle<>;
-  constexpr bool await_ready() noexcept { return false; }
-  void await_suspend(handle_type) noexcept {}
-  int await_resume() noexcept { return 1; }
-};
-
-class awaitable_unused_warn {
-public:
-  using handle_type = std::experimental::coroutine_handle<>;
-  constexpr bool await_ready() noexcept { return false; }
-  void await_suspend(handle_type) noexcept {}
-  [[nodiscard]] int await_resume() noexcept { return 1; }
-};
-
-template <class Await>
-struct check_warning_promise {
-  coro<check_warning_promise> get_return_object();
-  Await initial_suspend();
-  Await final_suspend() noexcept;
-  Await yield_value(int);
-  void return_void();
-  void unhandled_exception();
-};
-
-coro<check_warning_promise<awaitable_no_unused_warn>>
-test_no_unused_warning() {
-  co_await awaitable_no_unused_warn();
-  co_yield 42;
-}
-
-coro<check_warning_promise<awaitable_unused_warn>>
-test_unused_warning() {
-  co_await awaitable_unused_warn(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-  co_yield 42;                      // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-}
-
-struct missing_await_ready {
-  void await_suspend(std::experimental::coroutine_handle<>);
-  void await_resume();
-};
-struct missing_await_suspend {
-  bool await_ready();
-  void await_resume();
-};
-struct missing_await_resume {
-  bool await_ready();
-  void await_suspend(std::experimental::coroutine_handle<>);
-};
-
-void test_missing_awaitable_members() {
-  co_await missing_await_ready{};   // expected-error {{no member named 'await_ready' in 'missing_await_ready'}}
-  co_await missing_await_suspend{}; // expected-error {{no member named 'await_suspend' in 'missing_await_suspend'}}
-  co_await missing_await_resume{};  // expected-error {{no member named 'await_resume' in 'missing_await_resume'}}
-}
diff --git a/clang/test/SemaCXX/coroutines.cpp b/clang/test/SemaCXX/coroutines.cpp
--- a/clang/test/SemaCXX/coroutines.cpp
+++ b/clang/test/SemaCXX/coroutines.cpp
@@ -6,26 +6,27 @@
 // RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -fsyntax-only -verify=expected,cxx14_20          %s -fcxx-exceptions -fexceptions -Wunused-result
 
 void no_coroutine_traits_bad_arg_await() {
-  co_await a; // expected-error {{include <coroutine>}}
+  co_await a; // expected-error {{include <experimental/coroutine>}}
   // expected-error@-1 {{use of undeclared identifier 'a'}}
 }
 
 void no_coroutine_traits_bad_arg_yield() {
-  co_yield a; // expected-error {{include <coroutine>}}
+  co_yield a; // expected-error {{include <experimental/coroutine>}}
   // expected-error@-1 {{use of undeclared identifier 'a'}}
 }
 
 
 void no_coroutine_traits_bad_arg_return() {
-  co_return a; // expected-error {{include <coroutine>}}
+  co_return a; // expected-error {{include <experimental/coroutine>}}
   // expected-error@-1 {{use of undeclared identifier 'a'}}
 }
 
 void no_coroutine_traits() {
-  co_await 4; // expected-error {{std::coroutine_traits type was not found; include <coroutine>}}
+  co_await 4; // expected-error {{std::experimental::coroutine_traits type was not found; include <experimental/coroutine>}}
 }
 
 namespace std {
+namespace experimental {
 
 template <class... Args>
 struct void_t_imp {
@@ -44,11 +45,11 @@
 
 template <class Ret, class... Args>
 struct coroutine_traits : public traits_sfinae_base<Ret> {};
-} // end of namespace std
+}}  // namespace std::experimental
 
 template<typename Promise> struct coro {};
 template <typename Promise, typename... Ps>
-struct std::coroutine_traits<coro<Promise>, Ps...> {
+struct std::experimental::coroutine_traits<coro<Promise>, Ps...> {
   using promise_type = Promise;
 };
 
@@ -80,46 +81,47 @@
 };
 
 struct DummyVoidTag {};
-DummyVoidTag no_specialization() { // expected-error {{this function cannot be a coroutine: 'std::coroutine_traits<DummyVoidTag>' has no member named 'promise_type'}}
+DummyVoidTag no_specialization() { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<DummyVoidTag>' has no member named 'promise_type'}}
   co_await a;
 }
 
 template <typename... T>
-struct std::coroutine_traits<int, T...> {};
+struct std::experimental::coroutine_traits<int, T...> {};
 
-int no_promise_type() { // expected-error {{this function cannot be a coroutine: 'std::coroutine_traits<int>' has no member named 'promise_type'}}
+int no_promise_type() { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<int>' has no member named 'promise_type'}}
   co_await a;
 }
 
-int no_promise_type_multiple_awaits(int) { // expected-error {{this function cannot be a coroutine: 'std::coroutine_traits<int, int>' has no member named 'promise_type'}}
+int no_promise_type_multiple_awaits(int) { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<int, int>' has no member named 'promise_type'}}
   co_await a;
   co_await a;
 }
 
 template <>
-struct std::coroutine_traits<double, double> { typedef int promise_type; };
-double bad_promise_type(double) { // expected-error {{this function cannot be a coroutine: 'std::coroutine_traits<double, double>::promise_type' (aka 'int') is not a class}}
+struct std::experimental::coroutine_traits<double, double> { typedef int promise_type; };
+double bad_promise_type(double) { // expected-error {{this function cannot be a coroutine: 'experimental::coroutine_traits<double, double>::promise_type' (aka 'int') is not a class}}
   co_await a;
 }
 
 template <>
-struct std::coroutine_traits<double, int> {
+struct std::experimental::coroutine_traits<double, int> {
   struct promise_type {};
 };
 double bad_promise_type_2(int) { // expected-error {{no member named 'initial_suspend'}}
-  co_yield 0;                    // expected-error {{no member named 'yield_value' in 'std::coroutine_traits<double, int>::promise_type'}}
+  co_yield 0; // expected-error {{no member named 'yield_value' in 'std::experimental::coroutine_traits<double, int>::promise_type'}}
 }
 
 struct promise; // expected-note {{forward declaration}}
 struct promise_void;
 struct void_tag {};
 template <typename... T>
-struct std::coroutine_traits<void, T...> { using promise_type = promise; };
+struct std::experimental::coroutine_traits<void, T...> { using promise_type = promise; };
 template <typename... T>
-struct std::coroutine_traits<void, void_tag, T...> { using promise_type = promise_void; };
+struct std::experimental::coroutine_traits<void, void_tag, T...>
+{ using promise_type = promise_void; };
 
 // FIXME: This diagnostic is terrible.
-void undefined_promise() { // expected-error {{this function cannot be a coroutine: 'std::coroutine_traits<void>::promise_type' (aka 'promise') is an incomplete type}}
+void undefined_promise() { // expected-error {{this function cannot be a coroutine: 'experimental::coroutine_traits<void>::promise_type' (aka 'promise') is an incomplete type}}
   co_await a;
 }
 
@@ -146,12 +148,13 @@
   void unhandled_exception();
 };
 
-void no_coroutine_handle() { // expected-error {{std::coroutine_handle type was not found; include <coroutine> before defining a coroutine}}
+void no_coroutine_handle() { // expected-error {{std::experimental::coroutine_handle type was not found; include <experimental/coroutine> before defining a coroutine}}
   //expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
   co_return 5; //expected-note {{function is a coroutine due to use of 'co_return' here}}
 }
 
 namespace std {
+namespace experimental {
 template <class PromiseType = void>
 struct coroutine_handle {
   static coroutine_handle from_address(void *) noexcept;
@@ -162,7 +165,7 @@
   coroutine_handle(coroutine_handle<PromiseType>) noexcept;
   static coroutine_handle from_address(void *) noexcept;
 };
-} // namespace std
+}} // namespace std::experimental
 
 void yield() {
   co_yield 0;
@@ -526,7 +529,7 @@
 
 struct yield_fn_tag {};
 template <>
-struct std::coroutine_traits<void, yield_fn_tag> {
+struct std::experimental::coroutine_traits<void, yield_fn_tag> {
   struct promise_type {
     // FIXME: add an await_transform overload for functions
     awaitable yield_value(int());
@@ -744,7 +747,8 @@
 }
 template void ok_generic_lambda_coawait_PR41909<int>(); // expected-note {{in instantiation of function template specialization 'ok_generic_lambda_coawait_PR41909<int>' requested here}}
 
-template <> struct std::coroutine_traits<int, int, const char **> { using promise_type = promise; };
+template<> struct std::experimental::coroutine_traits<int, int, const char**>
+{ using promise_type = promise; };
 
 int main(int, const char**) {
   co_await a; // expected-error {{'co_await' cannot be used in the 'main' function}}
@@ -757,11 +761,12 @@
   void return_void();
   void unhandled_exception();
 };
-template <> struct std::coroutine_handle<good_promise_2> {};
+template<> struct std::experimental::coroutine_handle<good_promise_2> {};
 
-template <> struct std::coroutine_traits<float> { using promise_type = good_promise_2; };
+template<> struct std::experimental::coroutine_traits<float>
+{ using promise_type = good_promise_2; };
 
-float badly_specialized_coro_handle() { // expected-error {{std::coroutine_handle missing a member named 'from_address'}}
+float badly_specialized_coro_handle() { // expected-error {{std::experimental::coroutine_handle missing a member named 'from_address'}}
   //expected-note@-1 {{call to 'initial_suspend' implicitly required by the initial suspend point}}
   co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
 }
@@ -780,8 +785,8 @@
 
 struct promise_on_alloc_failure_tag {};
 
-template <>
-struct std::coroutine_traits<int, promise_on_alloc_failure_tag> {
+template<>
+struct std::experimental::coroutine_traits<int, promise_on_alloc_failure_tag> {
   struct promise_type {
     int get_return_object() {}
     suspend_always initial_suspend() { return {}; }
@@ -900,8 +905,8 @@
 }
 
 struct mismatch_gro_type_tag1 {};
-template <>
-struct std::coroutine_traits<int, mismatch_gro_type_tag1> {
+template<>
+struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag1> {
   struct promise_type {
     void get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
     suspend_always initial_suspend() { return {}; }
@@ -917,8 +922,8 @@
 }
 
 struct mismatch_gro_type_tag2 {};
-template <>
-struct std::coroutine_traits<int, mismatch_gro_type_tag2> {
+template<>
+struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag2> {
   struct promise_type {
     void *get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
     suspend_always initial_suspend() { return {}; }
@@ -935,8 +940,8 @@
 }
 
 struct mismatch_gro_type_tag3 {};
-template <>
-struct std::coroutine_traits<int, mismatch_gro_type_tag3> {
+template<>
+struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag3> {
   struct promise_type {
     int get_return_object() {}
     static void get_return_object_on_allocation_failure() {} //expected-note {{member 'get_return_object_on_allocation_failure' declared here}}
@@ -954,8 +959,8 @@
 
 
 struct mismatch_gro_type_tag4 {};
-template <>
-struct std::coroutine_traits<int, mismatch_gro_type_tag4> {
+template<>
+struct std::experimental::coroutine_traits<int, mismatch_gro_type_tag4> {
   struct promise_type {
     int get_return_object() {}
     static char *get_return_object_on_allocation_failure() {} //expected-note {{member 'get_return_object_on_allocation_failure' declared}}
@@ -987,13 +992,13 @@
 struct bad_await_suspend_return {
   bool await_ready();
   // expected-error@+1 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'char')}}
-  char await_suspend(std::coroutine_handle<>);
+  char await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 struct bad_await_ready_return {
   // expected-note@+1 {{return type of 'await_ready' is required to be contextually convertible to 'bool'}}
   void await_ready();
-  bool await_suspend(std::coroutine_handle<>);
+  bool await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 struct await_ready_explicit_bool {
@@ -1001,7 +1006,7 @@
     explicit operator bool() const;
   };
   BoolT await_ready();
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 template <class SuspendTy>
@@ -1009,7 +1014,7 @@
   bool await_ready();
   // expected-error@+2 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'bool &')}}
   // expected-error@+1 {{return type of 'await_suspend' is required to be 'void' or 'bool' (have 'bool &&')}}
-  SuspendTy await_suspend(std::coroutine_handle<>);
+  SuspendTy await_suspend(std::experimental::coroutine_handle<>);
   // cxx20_2b-warning@-1 {{volatile-qualified return type 'const volatile bool' is deprecated}}
   void await_resume();
 };
@@ -1069,7 +1074,7 @@
 
   template <class... Args>
   static constexpr bool MatchesArgs = IsSameV<T,
-                                              std::coroutine_traits<CoroMemberTag, Args...>>;
+                                              std::experimental::coroutine_traits<CoroMemberTag, Args...>>;
 };
 
 template <class T>
@@ -1081,7 +1086,7 @@
 
 template <class... CoroTraitsArgs>
 struct CoroMemberPromise {
-  using TraitsT = std::coroutine_traits<CoroTraitsArgs...>;
+  using TraitsT = std::experimental::coroutine_traits<CoroTraitsArgs...>;
   using TypeTestT = TypeTest<TraitsT>;
   using AwaitTestT = AwaitReturnsType<TypeTestT>;
 
@@ -1098,7 +1103,7 @@
 } // namespace CoroHandleMemberFunctionTest
 
 template <class... Args>
-struct ::std::coroutine_traits<CoroHandleMemberFunctionTest::CoroMemberTag, Args...> {
+struct ::std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::CoroMemberTag, Args...> {
   using promise_type = CoroHandleMemberFunctionTest::CoroMemberPromise<CoroHandleMemberFunctionTest::CoroMemberTag, Args...>;
 };
 
@@ -1184,16 +1189,16 @@
   }
 
   BadCoroMemberTag test_diagnostics() {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, CoroHandleMemberFunctionTest::TestType &>' has no member named 'promise_type'}}
+    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, CoroHandleMemberFunctionTest::TestType &>' has no member named 'promise_type'}}
     co_return;
   }
   BadCoroMemberTag test_diagnostics(int) const && {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, const CoroHandleMemberFunctionTest::TestType &&, int>' has no member named 'promise_type'}}
+    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, const CoroHandleMemberFunctionTest::TestType &&, int>' has no member named 'promise_type'}}
     co_return;
   }
 
   static BadCoroMemberTag test_static_diagnostics(long *) {
-    // expected-error@-1 {{this function cannot be a coroutine: 'std::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, long *>' has no member named 'promise_type'}}
+    // expected-error@-1 {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<CoroHandleMemberFunctionTest::BadCoroMemberTag, long *>' has no member named 'promise_type'}}
     co_return;
   }
 };
@@ -1305,7 +1310,7 @@
 
 coro<bad_promise_deleted_constructor>
 bad_coroutine_calls_deleted_promise_constructor() {
-  // expected-error@-1 {{call to deleted constructor of 'std::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_deleted_constructor>>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_deleted_constructor')}}
+  // expected-error@-1 {{call to deleted constructor of 'std::experimental::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_deleted_constructor>>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_deleted_constructor')}}
   co_return;
 }
 
@@ -1372,7 +1377,7 @@
 
 coro<bad_promise_no_matching_constructor>
 bad_coroutine_calls_with_no_matching_constructor(int, int) {
-  // expected-error@-1 {{call to deleted constructor of 'std::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor>, int, int>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor')}}
+  // expected-error@-1 {{call to deleted constructor of 'std::experimental::coroutine_traits<coro<CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor>, int, int>::promise_type' (aka 'CoroHandleMemberFunctionTest::bad_promise_no_matching_constructor')}}
   co_return;
 }
 
@@ -1388,7 +1393,7 @@
 
 class awaitable_no_unused_warn {
 public:
-  using handle_type = std::coroutine_handle<>;
+  using handle_type = std::experimental::coroutine_handle<>;
   constexpr bool await_ready() noexcept { return false; }
   void await_suspend(handle_type) noexcept {}
   int await_resume() noexcept { return 1; }
@@ -1397,7 +1402,7 @@
 
 class awaitable_unused_warn {
 public:
-  using handle_type = std::coroutine_handle<>;
+  using handle_type = std::experimental::coroutine_handle<>;
   constexpr bool await_ready() noexcept { return false; }
   void await_suspend(handle_type) noexcept {}
   [[nodiscard]] int await_resume() noexcept { return 1; }
@@ -1427,7 +1432,7 @@
 }
 
 struct missing_await_ready {
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
   void await_resume();
 };
 struct missing_await_suspend {
@@ -1436,7 +1441,7 @@
 };
 struct missing_await_resume {
   bool await_ready();
-  void await_suspend(std::coroutine_handle<>);
+  void await_suspend(std::experimental::coroutine_handle<>);
 };
 
 void test_missing_awaitable_members() {
diff --git a/clang/unittests/ASTMatchers/ASTMatchersTraversalTest.cpp b/clang/unittests/ASTMatchers/ASTMatchersTraversalTest.cpp
--- a/clang/unittests/ASTMatchers/ASTMatchersTraversalTest.cpp
+++ b/clang/unittests/ASTMatchers/ASTMatchersTraversalTest.cpp
@@ -623,6 +623,7 @@
   FileContentMappings M;
   M.push_back(std::make_pair("/coro_header", R"cpp(
 namespace std {
+namespace experimental {
 
 template <class... Args>
 struct void_t_imp {
@@ -641,7 +642,7 @@
 
 template <class Ret, class... Args>
 struct coroutine_traits : public traits_sfinae_base<Ret> {};
-}  // namespace std
+}}  // namespace std::experimental
 struct awaitable {
   bool await_ready() noexcept;
   template <typename F>
@@ -657,13 +658,14 @@
   void unhandled_exception();
 };
 template <typename... T>
-struct std::coroutine_traits<void, T...> { using promise_type = promise; };
+struct std::experimental::coroutine_traits<void, T...> { using promise_type = promise; };
 namespace std {
+namespace experimental {
 template <class PromiseType = void>
 struct coroutine_handle {
   static coroutine_handle from_address(void *) noexcept;
 };
-} // namespace std
+}} // namespace std::experimental
 )cpp"));
   StringRef CoReturnCode = R"cpp(
 #include <coro_header>