[clang-tools-extra] [clang-tidy] Ignore unused parameters in `rvalue-reference-param-not-moved check` (PR #69045)

[via cfe-commits]

https://github.com/AMS21 updated https://github.com/llvm/llvm-project/pull/69045

>From acf77633498bb0f8b67760628f0ac54f772ad1ac Mon Sep 17 00:00:00 2001
From: AMS21 <AMS21.github at gmail.com>
Date: Sat, 14 Oct 2023 10:26:36 +0200
Subject: [PATCH] [clang-tidy] Ignore unused parameters in
 `rvalue-reference-param-not-moved check`

With this patch we no longer issue a warning for unused parameters which
are marked as such.

This fixes #68209
---
 .../RvalueReferenceParamNotMovedCheck.cpp     |  3 +++
 clang-tools-extra/docs/ReleaseNotes.rst       |  4 +++
 .../rvalue-reference-param-not-moved.rst      | 10 ++++++++
 .../rvalue-reference-param-not-moved.cpp      | 25 +++++++++++++++++++
 4 files changed, 42 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/RvalueReferenceParamNotMovedCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/RvalueReferenceParamNotMovedCheck.cpp
index efcaffb45d9ad8a..88b00dc17470f32 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/RvalueReferenceParamNotMovedCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/RvalueReferenceParamNotMovedCheck.cpp
@@ -84,6 +84,9 @@ void RvalueReferenceParamNotMovedCheck::check(
   if (IgnoreUnnamedParams && Param->getName().empty())
     return;
 
+  if (!Param->isUsed() && Param->hasAttr<UnusedAttr>())
+    return;
+
   const auto *Function = dyn_cast<FunctionDecl>(Param->getDeclContext());
   if (!Function)
     return;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 03e5dc6f164af2a..c732d4904df13fa 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -237,6 +237,10 @@ Changes in existing checks
   <clang-tidy/checks/cppcoreguidelines/pro-type-vararg>` check to ignore
   false-positives in unevaluated context (e.g., ``decltype``, ``sizeof``, ...).
 
+- Improved :doc:`cppcoreguidelines-rvalue-reference-param-not-moved
+  <clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved>` check
+  to ignore unused parameters when they are marked as unused.
+
 - Improved :doc:`llvm-namespace-comment
   <clang-tidy/checks/llvm/namespace-comment>` check to provide fixes for
   ``inline`` namespaces in the same format as :program:`clang-format`.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved.rst b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved.rst
index 9ab4ae7871e46e4..ffa3a9d61e48e9d 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved.rst
@@ -18,6 +18,16 @@ Example:
     std::string Copy(Input); // Oops - forgot to std::move
   }
 
+Note that parameters that are unused and marked as such will not be diagnosed.
+
+Example:
+
+.. code-block:: c++
+
+  void conditional_use([[maybe_unused]] std::string&& Input) {
+    // No diagnostic here since Input is unused and marked as such
+  }
+
 Options
 -------
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/rvalue-reference-param-not-moved.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/rvalue-reference-param-not-moved.cpp
index 8f8e272e1e8a90d..a9b87567a08cc0a 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/rvalue-reference-param-not-moved.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/rvalue-reference-param-not-moved.cpp
@@ -333,3 +333,28 @@ void instantiate_a_class_template() {
   AClassTemplate<Obj&> withObjRef(o);
   withObjRef.never_moves(o);
 }
+
+namespace gh68209
+{
+  void f1([[maybe_unused]] int&& x) {}
+
+  void f2(__attribute__((unused)) int&& x) {}
+
+  void f3(int&& x) {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: rvalue reference parameter 'x' is never moved from inside the function body [cppcoreguidelines-rvalue-reference-param-not-moved]
+
+  template <typename T>
+  void f4([[maybe_unused]] T&& x) {}
+
+  template <typename T>
+  void f5(__attribute((unused)) T&& x) {}
+
+  template<typename T>
+  void f6(T&& x) {}
+
+  void f7([[maybe_unused]] int&& x) { x += 1; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:34: warning: rvalue reference parameter 'x' is never moved from inside the function body [cppcoreguidelines-rvalue-reference-param-not-moved]
+
+  void f8(__attribute__((unused)) int&& x) { x += 1; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:41: warning: rvalue reference parameter 'x' is never moved from inside the function body [cppcoreguidelines-rvalue-reference-param-not-moved]
+} // namespace gh68209