[clang] Do not trigger -Wmissing-noreturn on lambdas prior to C++23 (PR #154545)

[Carlos Galvez via cfe-commits]

https://github.com/carlosgalvezp created https://github.com/llvm/llvm-project/pull/154545

Fixes #154493

>From ad5814e0d775db9c455809bec7c2e80ab5c5cfc3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20G=C3=A1lvez?= <carlos.galvez at zenseact.com>
Date: Wed, 20 Aug 2025 13:46:58 +0000
Subject: [PATCH] Do not trigger -Wmissing-noreturn on lambdas prior to C++23

Fixes #154493
---
 clang/docs/ReleaseNotes.rst                         |  3 +++
 clang/lib/Sema/SemaDeclAttr.cpp                     |  5 +++++
 clang/test/SemaCXX/wmissing-noreturn-suggestion.cpp | 13 ++++++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5c780851ca589..5a837642ca99b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -188,6 +188,9 @@ Improvements to Clang's diagnostics
   potential misaligned members get processed before they can get discarded.
   (#GH144729)
 
+- Fixed false positive in ``-Wmissing-noreturn`` diagnostic when it was requiring the usage of
+  ``[[noreturn]]`` on lambdas before C++23 (#GH154493).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 7a185106e4c6e..8c3130a7d4735 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1989,6 +1989,11 @@ void clang::inferNoReturnAttr(Sema &S, const Decl *D) {
       isKnownToAlwaysThrow(FD)) {
     NonConstFD->addAttr(InferredNoReturnAttr::CreateImplicit(S.Context));
 
+    // [[noreturn]] can only be added to lambdas since C++23
+    if (const auto *MD = dyn_cast<CXXMethodDecl>(FD);
+        MD && !S.getLangOpts().CPlusPlus23 && isLambdaCallOperator(MD))
+      return;
+
     // Emit a diagnostic suggesting the function being marked [[noreturn]].
     S.Diag(FD->getLocation(), diag::warn_suggest_noreturn_function)
         << /*isFunction=*/0 << FD;
diff --git a/clang/test/SemaCXX/wmissing-noreturn-suggestion.cpp b/clang/test/SemaCXX/wmissing-noreturn-suggestion.cpp
index 8beffcd39e85c..ef70250f1f468 100644
--- a/clang/test/SemaCXX/wmissing-noreturn-suggestion.cpp
+++ b/clang/test/SemaCXX/wmissing-noreturn-suggestion.cpp
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -Wmissing-noreturn -verify %s
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -Wmissing-noreturn -verify -std=c++17 %s
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -Wmissing-noreturn -verify -std=c++23 %s
 
 namespace std {
   class string {
@@ -16,6 +17,16 @@ void throwError(const std::string& msg) { // expected-warning {{function 'throwE
   throw std::runtime_error(msg);
 }
 
+// We cannot use the [[noreturn]] attribute on lambdas until C++23
+void lambda(const std::string& msg) {
+#if __cplusplus >= 202302L
+  auto l1 = [&msg](){ throw std::runtime_error(msg); };  // expected-warning {{function 'operator()' could be declared with attribute 'noreturn'}}
+  auto l2 = [&msg] [[noreturn]] (){ throw std::runtime_error(msg); };
+#else
+  auto l1 = [&msg](){ throw std::runtime_error(msg); };
+#endif
+}
+
 // The non-void caller should not warn about missing return.
 int ensureZero(int i) {
   if (i == 0) return 0;