[clang] [coroutines] Introduce [[clang::coro_return_type]] and [[clang::coro_wrapper]] (PR #71945)

[Ilya Biryukov via cfe-commits]

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@@ -15811,6 +15813,20 @@ static void diagnoseImplicitlyRetainedSelf(Sema &S) {
           << FixItHint::CreateInsertion(P.first, "self->");
 }
 
+void Sema::CheckCoroutineWrapper(FunctionDecl *FD) {
+  if (!FD || getCurFunction()->isCoroutine())
+    return;
+  RecordDecl *RD = FD->getReturnType()->getAsRecordDecl();
+  if (!RD || !RD->getUnderlyingDecl()->hasAttr<CoroReturnTypeAttr>())
+    return;
+  // Allow `get_return_object()`.
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ilya-biryukov wrote:

NIT: you might want to add a mention in documentation that `PromiseType::get_return_object` are exempt of this analysis as it is a necessary implementation detail of any coroutine library.

https://github.com/llvm/llvm-project/pull/71945