[clang] Add separate C++23 extension flag for attrs on lambda (#74553)

Author: usx95

clang/docs/LanguageExtensions.rst

@@ -1483,6 +1483,7 @@ Conditional ``explicit``               __cpp_conditional_explicit       C++20
 ``using enum``                         __cpp_using_enum                 C++20         C++03
 ``if consteval``                       __cpp_if_consteval               C++23         C++20
 ``static operator()``                  __cpp_static_call_operator       C++23         C++03
+Attributes on Lambda-Expressions                                        C++23         C++11
 -------------------------------------- -------------------------------- ------------- -------------
 Designated initializers (N494)                                          C99           C89
 Array & element qualification (N2607)                                   C23           C89

clang/docs/ReleaseNotes.rst

@@ -156,6 +156,9 @@ C++23 Feature Support
   support for this feature is still experimental, the feature test macro ``__cpp_explicit_this_parameter``
   was not set in this version.
 
+- Added a separate warning to warn the use of attributes on lambdas as a C++23 extension
+  in previous language versions: ``-Wc++23-lambda-attributes``.
+
 C++2c Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1126,6 +1126,8 @@ def FutureAttrs : DiagGroup<"future-attribute-extensions", [CXX14Attrs,
                                                             CXX17Attrs,
                                                             CXX20Attrs]>;
 
+def CXX23AttrsOnLambda : DiagGroup<"c++23-lambda-attributes">;
+
 // A warning group for warnings about using C++11 features as extensions in
 // earlier C++ versions.
 def CXX11 : DiagGroup<"c++11-extensions", [CXX11ExtraSemi, CXX11InlineNamespace,
@@ -1145,7 +1147,7 @@ def CXX20 : DiagGroup<"c++20-extensions", [CXX20Designator, CXX20Attrs]>;
 
 // A warning group for warnings about using C++23 features as extensions in
 // earlier C++ versions.
-def CXX23 : DiagGroup<"c++23-extensions">;
+def CXX23 : DiagGroup<"c++23-extensions", [CXX23AttrsOnLambda]>;
 
 // A warning group for warnings about using C++26 features as extensions in
 // earlier C++ versions.

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1035,7 +1035,7 @@ def err_capture_default_first : Error<
   "capture default must be first">;
 def ext_decl_attrs_on_lambda : ExtWarn<
   "%select{an attribute specifier sequence|%0}1 in this position "
-  "is a C++23 extension">, InGroup<CXX23>;
+  "is a C++23 extension">, InGroup<CXX23AttrsOnLambda>;
 def ext_lambda_missing_parens : ExtWarn<
   "lambda without a parameter clause is a C++23 extension">,
   InGroup<CXX23>;

clang/test/SemaCXX/coro-lifetimebound.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++20 -fsyntax-only -verify -Wall -Wextra -Wno-error=unreachable-code -Wno-unused
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++20 -fsyntax-only -verify -Wall -Wextra -Wno-error=unreachable-code -Wno-unused -Wno-c++23-lambda-attributes
 
 #include "Inputs/std-coroutine.h"
 
@@ -64,14 +64,8 @@ Co<int> bar_coro(const int &b, int c) {
       : bar_coro(0, 1); // expected-warning {{returning address of local temporary object}}
 }
 
-#define CORO_WRAPPER \
-  _Pragma("clang diagnostic push") \
-  _Pragma("clang diagnostic ignored \"-Wc++23-extensions\"") \
-  [[clang::coro_wrapper]] \
-  _Pragma("clang diagnostic pop")
-
 void lambdas() {
-  auto unsafe_lambda = [] CORO_WRAPPER (int b) {
+  auto unsafe_lambda = [] [[clang::coro_wrapper]] (int b) {
     return foo_coro(b); // expected-warning {{address of stack memory associated with parameter}}
   };
   auto coro_lambda = [] (const int&) -> Co<int> {

clang/test/SemaCXX/coro-return-type-and-wrapper.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++20 -fsyntax-only -verify -Wall -Wextra
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -std=c++20 -fsyntax-only -verify -Wall -Wextra -Wno-c++23-lambda-attributes
 #include "Inputs/std-coroutine.h"
 
 using std::suspend_always;
@@ -45,11 +45,6 @@ Co<int> non_marked_wrapper(int b) { return foo_coro(b); }
 } // namespace using_decl
 
 namespace lambdas {
-#define CORO_WRAPPER \
-  _Pragma("clang diagnostic push") \
-  _Pragma("clang diagnostic ignored \"-Wc++23-extensions\"") \
-  [[clang::coro_wrapper]] \
-  _Pragma("clang diagnostic pop")
 
 void foo() {
   auto coro_lambda = []() -> Gen<int> {
@@ -59,7 +54,7 @@ void foo() {
   auto not_allowed_wrapper = []() -> Gen<int> {
     return foo_coro(1);
   };
-  auto allowed_wrapper = [] CORO_WRAPPER() -> Gen<int> {
+  auto allowed_wrapper = [] [[clang::coro_wrapper]] () -> Gen<int> {
     return foo_coro(1);
   };
 }