[libcxx-commits] [clang] [libcxx] [clang] Make error for [[clang::coro_wrapper]] be downgradable to a warning (PR #172910)

[via libcxx-commits]

https://github.com/higher-performance updated https://github.com/llvm/llvm-project/pull/172910

>From 246cf3e8d88170c3193e8eed50e42845dfb9b652 Mon Sep 17 00:00:00 2001
From: higher-performance <higher.performance.github at gmail.com>
Date: Thu, 18 Dec 2025 16:50:59 -0500
Subject: [PATCH] [clang] Make error for [[clang::coro_wrapper]] be
 downgradable to a warning

Given that both -Wreturn-type and -Wdangling are already warnings and not hard errors, it makes sense for this diagnostic to behave similarly.

This allows suppressing benign occurrences of the error in external headers whose source code is not in the user's direct control.
---
 clang/include/clang/Basic/DiagnosticSemaKinds.td      |  6 +++---
 clang/lib/Sema/SemaDecl.cpp                           |  2 +-
 clang/test/SemaCXX/coro-return-type-and-wrapper.cpp   | 11 ++++++-----
 libcxx/test/tools/clang_tidy_checks/hide_from_abi.cpp |  1 -
 4 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index f3c13841c4bf0..1b299bf459657 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -12743,10 +12743,10 @@ def err_conflicting_aligned_options : Error <
 def err_coro_invalid_addr_of_label : Error<
   "the GNU address of label extension is not allowed in coroutines"
 >;
-def err_coroutine_return_type : Error<
+def warn_coroutine_return_type : Warning<
   "function returns a type %0 marked with [[clang::coro_return_type]] but is neither a coroutine nor a coroutine wrapper; "
-  "non-coroutines should be marked with [[clang::coro_wrapper]] to allow returning coroutine return type"
->;
+  "non-coroutines should be marked with [[clang::coro_wrapper]] to allow returning coroutine return type">,
+  DefaultError;
 def warn_coroutine_type_aware_allocator_ignored : Warning <
   "type aware %0 will not be used for coroutine allocation">,
   InGroup<CoroTypeAwareAllocationFunction>;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6505bb6e5f7ed..c77f0e1c42cbb 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16440,7 +16440,7 @@ void Sema::CheckCoroutineWrapper(FunctionDecl *FD) {
   if (CanBeGetReturnObject(FD) || CanBeGetReturnTypeOnAllocFailure(FD))
     return;
   if (!FD->hasAttr<CoroWrapperAttr>())
-    Diag(FD->getLocation(), diag::err_coroutine_return_type) << RD;
+    Diag(FD->getLocation(), diag::warn_coroutine_return_type) << RD;
 }
 
 Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body, bool IsInstantiation,
diff --git a/clang/test/SemaCXX/coro-return-type-and-wrapper.cpp b/clang/test/SemaCXX/coro-return-type-and-wrapper.cpp
index b08e1c9c065a0..8d8d7ddbd2e9c 100644
--- a/clang/test/SemaCXX/coro-return-type-and-wrapper.cpp
+++ b/clang/test/SemaCXX/coro-return-type-and-wrapper.cpp
@@ -59,16 +59,17 @@ Co<int> non_marked_wrapper(int b) { return foo_coro(b); }
 namespace lambdas {
 
 void foo() {
-  auto coro_lambda = []() -> Gen<int> {
+  auto coro_lambda [[maybe_unused]] = []() -> Gen<int> {
     co_return 1;
   };
   // expected-error at +1 {{neither a coroutine nor a coroutine wrapper}}
-  auto not_allowed_wrapper = []() -> Gen<int> {
-    return foo_coro(1);
-  };
-  auto allowed_wrapper = [] [[clang::coro_wrapper]] () -> Gen<int> {
+  auto not_allowed_wrapper [[maybe_unused]] = []() -> Gen<int> {
     return foo_coro(1);
   };
+  auto allowed_wrapper [[maybe_unused]] =
+      [] [[clang::coro_wrapper]] () -> Gen<int> {
+        return foo_coro(1);
+      };
 }
 
 Gen<int> coro_containing_lambda() {
diff --git a/libcxx/test/tools/clang_tidy_checks/hide_from_abi.cpp b/libcxx/test/tools/clang_tidy_checks/hide_from_abi.cpp
index 38bf62019599e..f46ea3a5f733b 100644
--- a/libcxx/test/tools/clang_tidy_checks/hide_from_abi.cpp
+++ b/libcxx/test/tools/clang_tidy_checks/hide_from_abi.cpp
@@ -13,7 +13,6 @@
 
 namespace {
 AST_MATCHER(clang::ClassTemplateDecl, hasFullSpecializations) { return !Node.specializations().empty(); }
-AST_MATCHER(clang::CXXRecordDecl, isTrivial) { return Node.isTrivial(); }
 } // namespace
 
 namespace libcpp {