[clang] [Clang] Preserve coroutine parameter referenced state (PR #70973)

[Yuxuan Chen via cfe-commits]

https://github.com/yuxuanchen1997 updated https://github.com/llvm/llvm-project/pull/70973

>From 3be73f10d376739460f0c22d3292bc0de8f64b82 Mon Sep 17 00:00:00 2001
From: Yuxuan Chen <ych at meta.com>
Date: Wed, 1 Nov 2023 11:59:57 -0700
Subject: [PATCH] [Clang] Preserve coroutine parameter referenced state

---
 clang/lib/Sema/SemaCoroutine.cpp              |  6 ++++
 .../warn-unused-parameters-coroutine.cpp      | 34 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 clang/test/SemaCXX/warn-unused-parameters-coroutine.cpp

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 38ac406b14adadf..bee80db8d166a68 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -1965,9 +1965,15 @@ bool Sema::buildCoroutineParameterMoves(SourceLocation Loc) {
     if (PD->getType()->isDependentType())
       continue;
 
+    // Preserve the referenced state for unused parameter diagnostics.
+    bool DeclReferenced = PD->isReferenced();
+
     ExprResult PDRefExpr =
         BuildDeclRefExpr(PD, PD->getType().getNonReferenceType(),
                          ExprValueKind::VK_LValue, Loc); // FIXME: scope?
+
+    PD->setReferenced(DeclReferenced);
+
     if (PDRefExpr.isInvalid())
       return false;
 
diff --git a/clang/test/SemaCXX/warn-unused-parameters-coroutine.cpp b/clang/test/SemaCXX/warn-unused-parameters-coroutine.cpp
new file mode 100644
index 000000000000000..b4c01550f9f7883
--- /dev/null
+++ b/clang/test/SemaCXX/warn-unused-parameters-coroutine.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -fsyntax-only -Wunused-parameter -verify -std=c++20 %s
+
+#include "Inputs/std-coroutine.h"
+
+struct awaitable {
+  bool await_ready() noexcept;
+  void await_resume() noexcept;
+  void await_suspend(std::coroutine_handle<>) noexcept;
+};
+
+struct task : awaitable {
+  struct promise_type {
+    task get_return_object() noexcept;
+    awaitable initial_suspend() noexcept;
+    awaitable final_suspend() noexcept;
+    void unhandled_exception() noexcept;
+    void return_void() noexcept;
+  };
+};
+
+task foo(int a) { // expected-warning{{unused parameter 'a'}}
+  co_return;
+}
+
+task bar(int a, int b) { // expected-warning{{unused parameter 'b'}}
+  a = a + 1;
+  co_return;
+}
+
+void create_closure() {
+  auto closure = [](int c) -> task { // expected-warning{{unused parameter 'c'}}
+    co_return;
+  };
+}