[Coroutines] [Clang] Look up coroutine component in std namespace first

Summary: Now in libcxx and clang, all the coroutine components are
defined in std::experimental namespace.
And now the coroutine TS is merged into C++20. So in the working draft
like N4892, we could find the coroutine components is defined in std
namespace instead of std::experimental namespace.
And the coroutine support in clang seems to be relatively stable. So I
think it may be suitable to move the coroutine component into the
experiment namespace now.

But move the coroutine component into the std namespace may be an break
change. So I planned to split this change into two patch. One in clang
and other in libcxx.

This patch would make clang lookup coroutine_traits in std namespace
first. For the compatibility consideration, clang would lookup in
std::experimental namespace if it can't find definitions in std
namespace and emit a warning in this case. So the existing codes
wouldn't be break after update compiler.

Test Plan: check-clang, check-libcxx

Reviewed By: lxfind

Differential Revision: https://reviews.llvm.org/D108696

Author: ChuanqiXu9

clang-tools-extra/test/clang-tidy/checkers/Inputs/readability-identifier-naming/system/coroutines.h

@@ -1,7 +1,6 @@
 #pragma once
 
 namespace std {
-namespace experimental {
 
 template <typename ret_t, typename... args_t>
 struct coroutine_traits {
@@ -13,7 +12,6 @@ struct coroutine_handle {
   static constexpr coroutine_handle from_address(void *addr) noexcept { return {}; };
 };
 
-} // namespace experimental
 } // namespace std
 
 struct never_suspend {

clang/docs/LanguageExtensions.rst

@@ -2872,7 +2872,7 @@ C++ Coroutines support builtins
 
 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::experimental::coroutine_handle` type.
+standard library to implement `std::coroutine_handle` type.
 
 **Syntax**:
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10957,19 +10957,20 @@ def err_coroutine_invalid_func_context : Error<
   "|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 <experimental/coroutine> before defining "
-  "a coroutine">;
+  "%0 type was not found; include <coroutine> before defining "
+  "a coroutine; include <experimental/coroutine> if your version "
+  "of libcxx is less than 14.0">;
 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::experimental::coroutine_handle must be a class template">;
+  "std::coroutine_handle must be a class template">;
 def err_coroutine_handle_missing_member : Error<
-  "std::experimental::coroutine_handle missing a member named '%0'">;
+  "std::coroutine_handle missing a member named '%0'">;
 def err_malformed_std_coroutine_traits : Error<
-  "'std::experimental::coroutine_traits' must be a class template">;
+  "'std::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<
@@ -11011,6 +11012,10 @@ def note_await_ready_no_bool_conversion : Note<
 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"
 >;

clang/include/clang/Sema/Sema.h

@@ -1128,6 +1128,10 @@ class Sema final {
   /// 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;
@@ -5662,6 +5666,7 @@ class Sema final {
   NamespaceDecl *getOrCreateStdNamespace();
 
   NamespaceDecl *lookupStdExperimentalNamespace();
+  NamespaceDecl *getCachedCoroNamespace() { return CoroTraitsNamespaceCache; }
 
   CXXRecordDecl *getStdBadAlloc() const;
   EnumDecl *getStdAlignValT() const;
@@ -10218,8 +10223,11 @@ class Sema final {
   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);
+                                           SourceLocation FuncLoc,
+                                           NamespaceDecl *&Namespace);
   /// Check that the expression co_await promise.final_suspend() shall not be
   /// potentially-throwing.
   bool checkFinalSuspendNoThrow(const Stmt *FinalSuspend);

clang/lib/Sema/SemaCoroutine.cpp

@@ -53,15 +53,10 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
                                   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();
-  }
 
-  ClassTemplateDecl *CoroTraits = S.lookupCoroutineTraits(KwLoc, FuncLoc);
+  NamespaceDecl *CoroNamespace = nullptr;
+  ClassTemplateDecl *CoroTraits =
+      S.lookupCoroutineTraits(KwLoc, FuncLoc, CoroNamespace);
   if (!CoroTraits) {
     return QualType();
   }
@@ -122,7 +117,7 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
   QualType PromiseType = S.Context.getTypeDeclType(Promise);
 
   auto buildElaboratedType = [&]() {
-    auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, StdExp);
+    auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, CoroNamespace);
     NNS = NestedNameSpecifier::Create(S.Context, NNS, false,
                                       CoroTrait.getTypePtr());
     return S.Context.getElaboratedType(ETK_None, NNS, PromiseType);
@@ -141,20 +136,20 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
   return PromiseType;
 }
 
-/// Look up the std::experimental::coroutine_handle<PromiseType>.
+/// Look up the std::coroutine_handle<PromiseType>.
 static QualType lookupCoroutineHandleType(Sema &S, QualType PromiseType,
                                           SourceLocation Loc) {
   if (PromiseType.isNull())
     return QualType();
 
-  NamespaceDecl *StdExp = S.lookupStdExperimentalNamespace();
-  assert(StdExp && "Should already be diagnosed");
+  NamespaceDecl *CoroNamespace = S.getCachedCoroNamespace();
+  assert(CoroNamespace && "Should already be diagnosed");
 
   LookupResult Result(S, &S.PP.getIdentifierTable().get("coroutine_handle"),
                       Loc, Sema::LookupOrdinaryName);
-  if (!S.LookupQualifiedName(Result, StdExp)) {
+  if (!S.LookupQualifiedName(Result, CoroNamespace)) {
     S.Diag(Loc, diag::err_implied_coroutine_type_not_found)
-        << "std::experimental::coroutine_handle";
+        << "std::coroutine_handle";
     return QualType();
   }
 
@@ -1000,7 +995,7 @@ static Expr *buildStdNoThrowDeclRef(Sema &S, SourceLocation Loc) {
   LookupResult Result(S, &S.PP.getIdentifierTable().get("nothrow"), Loc,
                       Sema::LookupOrdinaryName);
   if (!S.LookupQualifiedName(Result, Std)) {
-    // FIXME: <experimental/coroutine> should have been included already.
+    // FIXME: <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);
@@ -1663,25 +1658,32 @@ StmtResult Sema::BuildCoroutineBodyStmt(CoroutineBodyStmt::CtorArgs Args) {
 }
 
 ClassTemplateDecl *Sema::lookupCoroutineTraits(SourceLocation KwLoc,
-                                               SourceLocation FuncLoc) {
+                                               SourceLocation FuncLoc,
+                                               NamespaceDecl *&Namespace) {
   if (!StdCoroutineTraitsCache) {
-    if (auto StdExp = lookupStdExperimentalNamespace()) {
-      LookupResult Result(*this,
-                          &PP.getIdentifierTable().get("coroutine_traits"),
-                          FuncLoc, LookupOrdinaryName);
-      if (!LookupQualifiedName(Result, StdExp)) {
+    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)) {
         Diag(KwLoc, diag::err_implied_coroutine_type_not_found)
-            << "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);
+            << "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;
 }

clang/test/AST/Inputs/std-coroutine.h

@@ -3,7 +3,6 @@
 #define STD_COROUTINE_H
 
 namespace std {
-namespace experimental {
 
 template <typename R, typename...> struct coroutine_traits {
   using promise_type = typename R::promise_type;
@@ -67,7 +66,6 @@ struct suspend_never {
   void await_resume() noexcept {}
 };
 
-} // namespace experimental
 } // namespace std
 
 #endif // STD_COROUTINE_H

clang/test/AST/coroutine-locals-cleanup.cpp

@@ -2,7 +2,7 @@
 
 #include "Inputs/std-coroutine.h"
 
-using namespace std::experimental;
+using namespace std;
 
 struct Task {
   struct promise_type {

clang/test/AST/coroutine-source-location-crash.cpp

@@ -11,7 +11,7 @@
 
 #include "Inputs/std-coroutine.h"
 
-using namespace std::experimental;
+using namespace std;
 
 struct A {
   bool await_ready();

clang/test/Analysis/more-dtors-cfg-output.cpp

@@ -275,32 +275,32 @@ void new_default_ctor_with_default_arg(long count) {
 #if CXX2A
 // Boilerplate needed to test co_return:
 
-namespace std::experimental {
-  template <typename Promise>
-  struct coroutine_handle {
-    static coroutine_handle from_address(void *) noexcept;
-  };
-}
+namespace std {
+template <typename Promise>
+struct coroutine_handle {
+  static coroutine_handle from_address(void *) noexcept;
+};
+} // namespace std
 
 struct TestPromise {
   TestPromise initial_suspend();
   TestPromise final_suspend() noexcept;
   bool await_ready() noexcept;
-  void await_suspend(const std::experimental::coroutine_handle<TestPromise> &) noexcept;
+  void await_suspend(const std::coroutine_handle<TestPromise> &) noexcept;
   void await_resume() noexcept;
   Foo return_value(const Bar &);
   Bar get_return_object();
   void unhandled_exception();
 };
 
-namespace std::experimental {
-  template <typename Ret, typename... Args>
-  struct coroutine_traits;
-  template <>
-  struct coroutine_traits<Bar> {
-      using promise_type = TestPromise;
-  };
-}
+namespace std {
+template <typename Ret, typename... Args>
+struct coroutine_traits;
+template <>
+struct coroutine_traits<Bar> {
+  using promise_type = TestPromise;
+};
+} // namespace std
 
 Bar coreturn() {
   co_return get_bar();

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::experimental {
+namespace std {
 template <typename R, typename... T> struct coroutine_traits {
   using promise_type = typename R::promise_type;
 };
@@ -20,11 +20,11 @@ template <class Promise> struct coroutine_handle : coroutine_handle<void> {
   coroutine_handle() = default;
   static coroutine_handle from_address(void *) noexcept;
 };
-}
+} // namespace std
 
 struct suspend_always {
   bool await_ready() noexcept;
-  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
+  void await_suspend(std::coroutine_handle<>) noexcept;
   void await_resume() noexcept;
 };
 
@@ -41,7 +41,7 @@ struct task {
 struct awaitable {
   task await() { (void)co_await *this; }
   bool await_ready() { return false; }
-  bool await_suspend(std::experimental::coroutine_handle<> awaiter) { return false; }
+  bool await_suspend(std::coroutine_handle<> awaiter) { return false; }
   bool await_resume() { return false; }
 };
 

clang/test/CodeGenCoroutines/Inputs/coroutine.h

@@ -1,6 +1,6 @@
 #pragma once
 
-namespace std { namespace experimental { inline namespace coroutines_v1 {
+namespace std {
 
 template <typename R, typename...> struct coroutine_traits {
   using promise_type = typename R::promise_type;
@@ -77,4 +77,4 @@ struct suspend_never {
   void await_resume() noexcept {}
 };
 
-}}}
+} // namespace std