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

[Ilya Biryukov via cfe-commits]

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@@ -15811,6 +15813,32 @@ static void diagnoseImplicitlyRetainedSelf(Sema &S) {
           << FixItHint::CreateInsertion(P.first, "self->");
 }
 
+// Return whether FD is `promise_type::get_return_object`.
+bool isGetReturnObject(FunctionDecl *FD) {
+  if (!FD->getDeclName().isIdentifier() ||
+      !FD->getName().equals("get_return_object") || !FD->param_empty())
+    return false;
+  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
+  if (!MD || !MD->isCXXInstanceMember())
+    return false;
+  RecordDecl *PromiseType = MD->getParent();
+  return PromiseType && PromiseType->getDeclName().isIdentifier() &&
+         PromiseType->getName().equals("promise_type");
+}
+
+void Sema::CheckCoroutineWrapper(FunctionDecl *FD) {
+  if (!getLangOpts().Coroutines || !FD || getCurFunction()->isCoroutine())
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ilya-biryukov wrote:

NIT: I believe we could skip a check for `getLangOpts().Coroutines`. It's safe to assume a low-level function like this is not called when coroutines are disabled, it's ok to make it the responsibility of the callers to ensure that.

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