[coroutines] Diagnose when promise types fail to declare either return_void or return_value.

Summary:
According to the PDTS it's perfectly legal to have a promise type that defines neither `return_value` nor `return_void`. However a coroutine that uses such a promise type will almost always have UB, because it can never `co_return`.

This patch changes Clang to diagnose such cases as an error. It also cleans up some of the diagnostic messages relating to member lookup in the promise type.

Reviewers: GorNishanov, rsmith

Reviewed By: GorNishanov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D33534

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303868 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 60 insertions, 37 deletions

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 60039fac6e..81eea5e683 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6303,6 +6303,8 @@ def warn_ambiguous_suitable_delete_function_found : Warning<
   InGroup<DiagGroup<"ambiguous-delete">>;
 def note_member_declared_here : Note<
   "member %0 declared here">;
+def note_member_first_declared_here : Note<
+  "member %0 first declared here">;
 def err_decrement_bool : Error<"cannot decrement expression of type bool">;
 def warn_increment_bool : Warning<
   "incrementing expression of type bool is deprecated and "
@@ -8918,8 +8920,6 @@ def err_return_in_coroutine : Error<
   "return statement not allowed in coroutine; did you mean 'co_return'?">;
 def note_declared_coroutine_here : Note<
   "function is a coroutine due to use of '%0' here">;
-def note_promise_member_declared_here : Note<
-  "'%0' is declared here">;
 def err_coroutine_objc_method : Error<
   "Objective-C methods as coroutines are not yet supported">;
 def err_coroutine_unevaluated_context : Error<
@@ -8954,8 +8954,10 @@ def err_coroutine_promise_type_incomplete : Error<
 def err_coroutine_type_missing_specialization : Error<
   "this function cannot be a coroutine: missing definition of "
   "specialization %q0">;
-def err_coroutine_promise_return_ill_formed : Error<
-  "%0 declares both 'return_value' and 'return_void'">;
+def err_coroutine_promise_incompatible_return_functions : Error<
+  "the coroutine promise type %0 declares both 'return_value' and 'return_void'">;
+def err_coroutine_promise_requires_return_function : Error<
+  "the coroutine promise type %0 must declare either 'return_value' or 'return_void'">;
 def note_coroutine_promise_implicit_await_transform_required_here : Note<
   "call to 'await_transform' implicitly required by 'co_await' here">;
 def note_coroutine_promise_suspend_implicitly_required : Note<
diff --git a/lib/Sema/SemaCoroutine.cpp b/lib/Sema/SemaCoroutine.cpp
index 45b3a48d15..009380df0e 100644
--- a/lib/Sema/SemaCoroutine.cpp
+++ b/lib/Sema/SemaCoroutine.cpp
@@ -23,14 +23,22 @@
 using namespace clang;
 using namespace sema;
 
-static bool lookupMember(Sema &S, const char *Name, CXXRecordDecl *RD,
-                         SourceLocation Loc) {
+static LookupResult lookupMember(Sema &S, const char *Name, CXXRecordDecl *RD,
+                                 SourceLocation Loc, bool &Res) {
   DeclarationName DN = S.PP.getIdentifierInfo(Name);
   LookupResult LR(S, DN, Loc, Sema::LookupMemberName);
   // Suppress diagnostics when a private member is selected. The same warnings
   // will be produced again when building the call.
   LR.suppressDiagnostics();
-  return S.LookupQualifiedName(LR, RD);
+  Res = S.LookupQualifiedName(LR, RD);
+  return LR;
+}
+
+static bool lookupMember(Sema &S, const char *Name, CXXRecordDecl *RD,
+                         SourceLocation Loc) {
+  bool Res;
+  lookupMember(S, Name, RD, Loc, Res);
+  return Res;
 }
 
 /// Look up the std::coroutine_traits<...>::promise_type for the given
@@ -861,9 +869,8 @@ bool CoroutineStmtBuilder::makeReturnOnAllocFailure() {
   StmtResult ReturnStmt =
       S.BuildReturnStmt(Loc, ReturnObjectOnAllocationFailure.get());
   if (ReturnStmt.isInvalid()) {
-    S.Diag(Found.getFoundDecl()->getLocation(),
-           diag::note_promise_member_declared_here)
-        << DN.getAsString();
+    S.Diag(Found.getFoundDecl()->getLocation(), diag::note_member_declared_here)
+        << DN;
     S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
         << Fn.getFirstCoroutineStmtKeyword();
     return false;
@@ -993,13 +1000,32 @@ bool CoroutineStmtBuilder::makeOnFallthrough() {
   // [dcl.fct.def.coroutine]/4
   // The unqualified-ids 'return_void' and 'return_value' are looked up in
   // the scope of class P. If both are found, the program is ill-formed.
-  const bool HasRVoid = lookupMember(S, "return_void", PromiseRecordDecl, Loc);
-  const bool HasRValue = lookupMember(S, "return_value", PromiseRecordDecl, Loc);
+  bool HasRVoid, HasRValue;
+  LookupResult LRVoid =
+      lookupMember(S, "return_void", PromiseRecordDecl, Loc, HasRVoid);
+  LookupResult LRValue =
+      lookupMember(S, "return_value", PromiseRecordDecl, Loc, HasRValue);
 
   StmtResult Fallthrough;
   if (HasRVoid && HasRValue) {
     // FIXME Improve this diagnostic
-    S.Diag(FD.getLocation(), diag::err_coroutine_promise_return_ill_formed)
+    S.Diag(FD.getLocation(),
+           diag::err_coroutine_promise_incompatible_return_functions)
+        << PromiseRecordDecl;
+    S.Diag(LRVoid.getRepresentativeDecl()->getLocation(),
+           diag::note_member_first_declared_here)
+        << LRVoid.getLookupName();
+    S.Diag(LRValue.getRepresentativeDecl()->getLocation(),
+           diag::note_member_first_declared_here)
+        << LRValue.getLookupName();
+    return false;
+  } else if (!HasRVoid && !HasRValue) {
+    // FIXME: The PDTS currently specifies this case as UB, not ill-formed.
+    // However we still diagnose this as an error since until the PDTS is fixed.
+    S.Diag(FD.getLocation(),
+           diag::err_coroutine_promise_requires_return_function)
+        << PromiseRecordDecl;
+    S.Diag(PromiseRecordDecl->getLocation(), diag::note_defined_here)
         << PromiseRecordDecl;
     return false;
   } else if (HasRVoid) {
@@ -1074,8 +1100,8 @@ bool CoroutineStmtBuilder::makeReturnObject() {
 static void noteMemberDeclaredHere(Sema &S, Expr *E, FunctionScopeInfo &Fn) {
   if (auto *MbrRef = dyn_cast<CXXMemberCallExpr>(E)) {
     auto *MethodDecl = MbrRef->getMethodDecl();
-    S.Diag(MethodDecl->getLocation(), diag::note_promise_member_declared_here)
-        << MethodDecl->getName();
+    S.Diag(MethodDecl->getLocation(), diag::note_member_declared_here)
+        << MethodDecl;
   }
   S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
       << Fn.getFirstCoroutineStmtKeyword();
diff --git a/test/SemaCXX/coreturn.cpp b/test/SemaCXX/coreturn.cpp
index 8bdf03ec67..0ec94d1b59 100644
--- a/test/SemaCXX/coreturn.cpp
+++ b/test/SemaCXX/coreturn.cpp
@@ -138,16 +138,3 @@ VoidTagReturnValue test11(bool b) {
   if (b)
     co_return 42;
 } // expected-warning {{control may reach end of coroutine}}
-
-// FIXME: Promise types that declare neither return_value nor return_void
-// should be ill-formed. This test should be removed when that is fixed.
-VoidTagNoReturn test12() {
-  co_await a;
-} // expected-warning {{control reaches end of coroutine}}
-
-// FIXME: Promise types that declare neither return_value nor return_void
-// should be ill-formed. This test should be removed when that is fixed.
-VoidTagNoReturn test13(bool b) {
-  if (b)
-    co_await a;
-} // expected-warning {{control reaches end of coroutine}}
diff --git a/test/SemaCXX/coroutines.cpp b/test/SemaCXX/coroutines.cpp
index 4588586d00..cfd32dc1bb 100644
--- a/test/SemaCXX/coroutines.cpp
+++ b/test/SemaCXX/coroutines.cpp
@@ -347,6 +347,7 @@ namespace dependent_operator_co_await_lookup {
     ::adl_ns::coawait_arg_type final_suspend();
     transformed await_transform(transform_awaitable);
     void unhandled_exception();
+    void return_void();
   };
   template <class AwaitArg>
   struct basic_promise {
@@ -355,6 +356,7 @@ namespace dependent_operator_co_await_lookup {
     awaitable initial_suspend();
     awaitable final_suspend();
     void unhandled_exception();
+    void return_void();
   };
 
   awaitable operator co_await(await_arg_1);
@@ -473,6 +475,7 @@ struct bad_promise_1 {
   suspend_always initial_suspend();
   suspend_always final_suspend();
   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;
@@ -483,6 +486,7 @@ struct bad_promise_2 {
   // FIXME: We shouldn't offer a typo-correction here!
   suspend_always final_suspend(); // expected-note {{here}}
   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'}}
@@ -494,6 +498,7 @@ struct bad_promise_3 {
   // FIXME: We shouldn't offer a typo-correction here!
   suspend_always initial_suspend(); // expected-note {{here}}
   void unhandled_exception();
+  void return_void();
 };
 coro<bad_promise_3> missing_final_suspend() { // expected-error {{no member named 'final_suspend' in 'bad_promise_3'}}
   co_await a;
@@ -503,6 +508,7 @@ struct bad_promise_4 {
   coro<bad_promise_4> get_return_object();
   not_awaitable initial_suspend();
   suspend_always final_suspend();
+  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'}}
@@ -514,6 +520,7 @@ struct bad_promise_5 {
   coro<bad_promise_5> get_return_object();
   suspend_always initial_suspend();
   not_awaitable final_suspend();
+  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'}}
@@ -526,8 +533,8 @@ struct bad_promise_6 {
   suspend_always initial_suspend();
   suspend_always final_suspend();
   void unhandled_exception();
-  void return_void();
-  void return_value(int) const;
+  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'}}
@@ -751,7 +758,7 @@ 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 {{'get_return_object' is declared here}}
+    void get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
     suspend_always initial_suspend() { return {}; }
     suspend_always final_suspend() { return {}; }
     void return_void() {}
@@ -768,7 +775,7 @@ 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 {{'get_return_object' is declared here}}
+    void *get_return_object() {} //expected-note {{member 'get_return_object' declared here}}
     suspend_always initial_suspend() { return {}; }
     suspend_always final_suspend() { return {}; }
     void return_void() {}
@@ -786,7 +793,7 @@ 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 {{'get_return_object_on_allocation_failure' is declared here}}
+    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() { return {}; }
     void return_void() {}
@@ -805,7 +812,7 @@ 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 {{'get_return_object_on_allocation_failure' is declared here}}
+    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() { return {}; }
     void return_void() {}
@@ -818,14 +825,15 @@ extern "C" int f(mismatch_gro_type_tag4) {
   co_return; //expected-note {{function is a coroutine due to use of 'co_return' here}}
 }
 
-struct bad_promise_no_return_func {
+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();
   void unhandled_exception();
 };
-// FIXME: Make this ill-formed because the promise type declares
-// neither return_value(...) or return_void().
+// 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;
 }