c++: Implement C++26 P3176R1 - The Oxford variadic comma

While we are already in stage3, I wonder if implementing this small paper
wouldn't be useful even for GCC 15, so that we have in the GCC world one
extra year of deprecation of variadic ellipsis without preceding comma.

The paper just deprecates something, I'd hope most of the C++ code in the
wild when it uses variadic functions at all uses the comma before the
ellipsis.

2024-11-30  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c.opt (Wdeprecated-variadic-comma-omission): New option.
	* c.opt.urls: Regenerate.
	* c-opts.cc (c_common_post_options): Default to
	-Wdeprecated-variadic-comma-omission for C++26 or -Wpedantic.
gcc/cp/
	* parser.cc: Implement C++26 P3176R1 - The Oxford variadic comma.
	(cp_parser_parameter_declaration_clause): Emit
	-Wdeprecated-variadic-comma-omission warnings.
gcc/
	* doc/invoke.texi (-Wdeprecated-variadic-comma-omission): Document.
gcc/testsuite/
	* g++.dg/cpp26/variadic-comma1.C: New test.
	* g++.dg/cpp26/variadic-comma2.C: New test.
	* g++.dg/cpp26/variadic-comma3.C: New test.
	* g++.dg/cpp26/variadic-comma4.C: New test.
	* g++.dg/cpp26/variadic-comma5.C: New test.
	* g++.dg/cpp1z/fold10.C: Expect a warning for C++26.
	* g++.dg/ext/attrib33.C: Likewise.
	* g++.dg/cpp1y/lambda-generic-variadic19.C: Likewise.
	* g++.dg/cpp2a/lambda-generic10.C: Likewise.
	* g++.dg/cpp0x/lambda/lambda-const3.C: Likewise.
	* g++.dg/cpp0x/variadic164.C: Likewise.
	* g++.dg/cpp0x/variadic17.C: Likewise.
	* g++.dg/cpp0x/udlit-args-neg.C: Likewise.
	* g++.dg/cpp0x/variadic28.C: Likewise.
	* g++.dg/cpp0x/gen-attrs-33.C: Likewise.
	* g++.dg/cpp23/explicit-obj-diagnostics3.C: Likewise.
	* g++.old-deja/g++.law/operators15.C: Likewise.
	* g++.old-deja/g++.mike/p811.C: Likewise.
	* g++.old-deja/g++.mike/p12306.C (printf): Add , before ... .
	* g++.dg/analyzer/fd-bind-pr107783.C (bind): Likewise.
	* g++.dg/cpp0x/vt-65790.C (printf): Likewise.
libstdc++-v3/
	* include/std/functional (_Bind_check_arity): Add , before ... .
	* include/bits/refwrap.h (_Mem_fn_traits, _Weak_result_type_impl):
	Likewise.
	* include/tr1/type_traits (is_function): Likewise.

26 files changed, 138 insertions, 32 deletions

diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index 0871eb3..7d139a7 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1061,6 +1061,11 @@ c_common_post_options (const char **pfilename)
 		       warn_array_compare,
 		       warn_array_compare || deprecated_in (cxx20));
 
+  /* -Wdeprecated-variadic-comma-omission is enabled by default in C++26.  */
+  SET_OPTION_IF_UNSET (&global_options, &global_options_set,
+		       warn_deprecated_variadic_comma_omission,
+		       deprecated_in (cxx26));
+
   /* -Wtemplate-id-cdtor is enabled by default in C++20.  */
   SET_OPTION_IF_UNSET (&global_options, &global_options_set,
 		       warn_template_id_cdtor,
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 467d361..0d25556 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -672,6 +672,10 @@ Wdeprecated-non-prototype
 C ObjC Var(warn_deprecated_non_prototype) Init(-1) Warning
 Warn about calls with arguments to functions declared without parameters.
 
+Wdeprecated-variadic-comma-omission
+C++ ObjC++ Var(warn_deprecated_variadic_comma_omission) Warning
+Warn about deprecated omission of comma before ... in varargs function declaration.
+
 Wdesignated-init
 C ObjC Var(warn_designated_init) Init(1) Warning
 Warn about positional initialization of structs requiring designated initializers.
diff --git a/gcc/c-family/c.opt.urls b/gcc/c-family/c.opt.urls
index 56c814e..8fbe3bd 100644
--- a/gcc/c-family/c.opt.urls
+++ b/gcc/c-family/c.opt.urls
@@ -310,6 +310,9 @@ UrlSuffix(gcc/C_002b_002b-Dialect-Options.html#index-Wdeprecated-literal-operato
 Wdeprecated-non-prototype
 UrlSuffix(gcc/Warning-Options.html#index-Wdeprecated-non-prototype)
 
+Wdeprecated-variadic-comma-omission
+UrlSuffix(gcc/C_002b_002b-Dialect-Options.html#index-Wdeprecated-variadic-comma-omission)
+
 Wdesignated-init
 UrlSuffix(gcc/Warning-Options.html#index-Wdesignated-init)
 
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index f519ab0..94069d7 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25770,6 +25770,16 @@ cp_parser_parameter_declaration_clause (cp_parser* parser,
      omitted.  */
   else if (token->type == CPP_ELLIPSIS)
     {
+      /* Deprecated by P3176R1 in C++26.  */
+      if (warn_deprecated_variadic_comma_omission)
+	{
+	  gcc_rich_location richloc (token->location);
+	  richloc.add_fixit_insert_before (", ");
+	  warning_at (&richloc, OPT_Wdeprecated_variadic_comma_omission,
+		      "omission of %<,%> before varargs %<...%> is "
+		      "deprecated in C++26");
+	}
+
       /* Consume the `...' token.  */
       cp_lexer_consume_token (parser->lexer);
       /* And remember that we saw it.  */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 18a5754..fa2532f 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4069,6 +4069,22 @@ string operator "" _i18n(const char*, std::size_t); // deprecated
 string operator ""_i18n(const char*, std::size_t); // preferred
 @end smallexample
 
+@opindex Wdeprecated-variadic-comma-omission
+@opindex Wno-deprecated-variadic-comma-omission
+@item -Wdeprecated-variadic-comma-omission @r{(C++ and Objective-C++ only)}
+Warn that omitting a comma before the varargs @code{...} at the end of
+a function parameter list is deprecated.  This warning is enabled by
+default in C++26, or with explicit @option{-Wdeprecated}.
+
+@smallexample
+void f1(int...); // deprecated
+void f1(int, ...); // preferred
+template <typename ...T>
+void f2(T...); // ok
+template <typename ...T>
+void f3(T......); // deprecated
+@end smallexample
+
 @opindex Welaborated-enum-base
 @opindex Wno-elaborated-enum-base
 @item -Wno-elaborated-enum-base
@@ -10348,8 +10364,9 @@ In C++, explicitly specifying @option{-Wdeprecated} also enables
 warnings about some features that are deprecated in later language
 standards, specifically @option{-Wcomma-subscript},
 @option{-Wvolatile}, @option{-Wdeprecated-enum-float-conversion},
-@option{-Wdeprecated-enum-enum-conversion}, and
-@option{-Wdeprecated-literal-operator}.
+@option{-Wdeprecated-enum-enum-conversion},
+@option{-Wdeprecated-literal-operator}, and
+@option{-Wdeprecated-variadic-comma-omission}.
 
 @opindex Wno-deprecated-declarations
 @opindex Wdeprecated-declarations
diff --git a/gcc/testsuite/g++.dg/analyzer/fd-bind-pr107783.C b/gcc/testsuite/g++.dg/analyzer/fd-bind-pr107783.C
index eb5e23c..318e148 100644
--- a/gcc/testsuite/g++.dg/analyzer/fd-bind-pr107783.C
+++ b/gcc/testsuite/g++.dg/analyzer/fd-bind-pr107783.C
@@ -7,5 +7,5 @@ struct _Bind {
   _Bind(_Bind &);
 };
 template <typename _Func, typename _BoundArgs>
-_Bind bind(_Func, _BoundArgs &&...);
+_Bind bind(_Func, _BoundArgs &&, ...);
 void test01() { bind(minus(), _2, _1); }
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-33.C b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-33.C
index efb2a1a..485d349 100644
--- a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-33.C
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-33.C
@@ -5,7 +5,7 @@
 template <int N>
 struct T
 {
-  void foo [[gnu::format (printf,2,3)]] (char const * ...);
+  void foo [[gnu::format (printf,2,3)]] (char const * ...);	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 };
 
 template struct T<3>;
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const3.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const3.C
index a1ffadd..1767dd7 100644
--- a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const3.C
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const3.C
@@ -7,7 +7,7 @@ struct FF
 {
   template < class F, class ... Ts >
   void
-  operator () (F & ...)
+  operator () (F & ...)			// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
   {
     const int n = sizeof ... (Ts) + 1;
     void *mutexes[n];
diff --git a/gcc/testsuite/g++.dg/cpp0x/udlit-args-neg.C b/gcc/testsuite/g++.dg/cpp0x/udlit-args-neg.C
index 72cb4b4..2750888 100644
--- a/gcc/testsuite/g++.dg/cpp0x/udlit-args-neg.C
+++ b/gcc/testsuite/g++.dg/cpp0x/udlit-args-neg.C
@@ -27,6 +27,7 @@ operator ""_Foo(const char16_t *);	// { dg-error "1:.Foo operator\"\"_Foo\\(cons
 
 Foo
 operator ""_Foo(char...);	// { dg-error "1:.Foo operator\"\"_Foo\\(char, \\.\\.\\.\\). has invalid argument list" }
+				// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } .-1 }
 
 Foo
 operator ""_Foo(unsigned long long int, char);	// { dg-error "1:.Foo operator\"\"_Foo\\(long long unsigned int, char\\). has invalid argument list" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic164.C b/gcc/testsuite/g++.dg/cpp0x/variadic164.C
index 8f9cdb1..a385534 100644
--- a/gcc/testsuite/g++.dg/cpp0x/variadic164.C
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic164.C
@@ -8,5 +8,5 @@ template <typename Tuple, typename... Tuples, int... ElementIndices,
           typename =
               typename tuple<slice_result<ElementIndices, Tuples...>,
                              slice_result<ElementIndices, Tuples...>...>::type> // { dg-error "parameter pack" }
-void zip_with(Tuple...);
+void zip_with(Tuple...);	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 decltype(zip_with(0)) d;	// { dg-error "no match" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic17.C b/gcc/testsuite/g++.dg/cpp0x/variadic17.C
index d54022a..4791bb4 100644
--- a/gcc/testsuite/g++.dg/cpp0x/variadic17.C
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic17.C
@@ -2,7 +2,7 @@
 template<typename R, typename... ArgTypes>
 struct make_function_type
 {
-  typedef R type(const ArgTypes&......);
+  typedef R type(const ArgTypes&......);		// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 };
 
 template<typename T, typename U>
@@ -16,6 +16,6 @@ struct is_same<T, T> {
 };
 
 int a0[is_same<make_function_type<int>::type, int(...)>::value? 1 : -1];
-int a1[is_same<make_function_type<int, float>::type, int(const float&...)>::value? 1 : -1];
+int a1[is_same<make_function_type<int, float>::type, int(const float&...)>::value? 1 : -1];		// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 int a2[is_same<make_function_type<int, float>::type, int(const float&,...)>::value? 1 : -1];
-int a3[is_same<make_function_type<int, float, double>::type, int(const float&, double const&...)>::value? 1 : -1];
+int a3[is_same<make_function_type<int, float, double>::type, int(const float&, double const&...)>::value? 1 : -1];		// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic28.C b/gcc/testsuite/g++.dg/cpp0x/variadic28.C
index b027861..57f6d23 100644
--- a/gcc/testsuite/g++.dg/cpp0x/variadic28.C
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic28.C
@@ -3,7 +3,7 @@ template<typename Signature>
 struct function_traits;
 
 template<typename R, typename... ArgTypes>
-struct function_traits<R(ArgTypes......)> {
+struct function_traits<R(ArgTypes......)> {	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
   typedef R result_type;
 };
 
@@ -17,9 +17,9 @@ struct same_type<T, T> {
   static const bool value = true;
 };
 
-int a0[same_type<function_traits<int(double, char...)>::result_type, int>::value? 1 : -1];
+int a0[same_type<function_traits<int(double, char...)>::result_type, int>::value? 1 : -1];	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 int a1[same_type<function_traits<int(double, char,...)>::result_type, int>::value? 1 : -1];
 int a2[same_type<function_traits<int(char,...)>::result_type, int>::value? 1 : -1];
 int a3[same_type<function_traits<int(...)>::result_type, int>::value? 1 : -1];
-int a4[same_type<function_traits<int(double x, char...)>::result_type, int>::value? 1 : -1];
-int a5[same_type<function_traits<int(double, char y...)>::result_type, int>::value? 1 : -1];
+int a4[same_type<function_traits<int(double x, char...)>::result_type, int>::value? 1 : -1];	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
+int a5[same_type<function_traits<int(double, char y...)>::result_type, int>::value? 1 : -1];	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-65790.C b/gcc/testsuite/g++.dg/cpp0x/vt-65790.C
index 477e988..4e89963 100644
--- a/gcc/testsuite/g++.dg/cpp0x/vt-65790.C
+++ b/gcc/testsuite/g++.dg/cpp0x/vt-65790.C
@@ -1,7 +1,7 @@
 // PR c++/65790
 // { dg-do compile { target c++11 } }
 
-extern "C" int printf(const char* ...);
+extern "C" int printf(const char*, ...);
 
 namespace std
 {
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-variadic19.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-variadic19.C
index e78677d..0fb873d 100644
--- a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-variadic19.C
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-variadic19.C
@@ -1,4 +1,4 @@
 // PR c++/86728
 // { dg-do compile { target c++14 } }
 
-auto c = [](auto x ...) { };
+auto c = [](auto x ...) { };	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
diff --git a/gcc/testsuite/g++.dg/cpp1z/fold10.C b/gcc/testsuite/g++.dg/cpp1z/fold10.C
index 1bd39a0..87aee5b 100644
--- a/gcc/testsuite/g++.dg/cpp1z/fold10.C
+++ b/gcc/testsuite/g++.dg/cpp1z/fold10.C
@@ -4,7 +4,7 @@
 template <int...> struct seq {};
 template <bool> struct S {
     template <typename Args>
-    constexpr static void call(Args&&...) {}
+    constexpr static void call(Args&&...) {}	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 };
 
 template <int ...Idx,typename ...Args>
diff --git a/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics3.C b/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics3.C
index f6a892e..4ff13af 100644
--- a/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics3.C
+++ b/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics3.C
@@ -24,7 +24,7 @@ void S::f12(this S s = {}) {} // { dg-error "an explicit object parameter may no
 
 struct S0 {
   template<typename Selves>
-  void f(this Selves...) {}
+  void f(this Selves...) {}	    // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void g(this Selves... selves) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -37,7 +37,7 @@ struct S0 {
   void k(this Selves...) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
 
   template<typename Selves>
-  void fd(this Selves...);
+  void fd(this Selves...);	   // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void gd(this Selves... selves);  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -52,7 +52,7 @@ struct S0 {
 
 struct S1 {
   template<typename Selves>
-  void f(this Selves&...) {}
+  void f(this Selves&...) {}	     // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void g(this Selves&... selves) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -65,7 +65,7 @@ struct S1 {
   void k(this Selves&...) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
 
   template<typename Selves>
-  void fd(this Selves&...);
+  void fd(this Selves&...);	    // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void gd(this Selves&... selves);  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -80,7 +80,7 @@ struct S1 {
 
 struct S2 {
   template<typename Selves>
-  void f(this Selves&&...) {}
+  void f(this Selves&&...) {}	      // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void g(this Selves&&... selves) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -93,7 +93,7 @@ struct S2 {
   void k(this Selves&&...) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
 
   template<typename Selves>
-  void fd(this Selves&&...);
+  void fd(this Selves&&...);	     // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void gd(this Selves&&... selves);  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -108,7 +108,7 @@ struct S2 {
 
 struct S3 {
   template<typename Selves>
-  void f(this Selves const&...) {}
+  void f(this Selves const&...) {}	   // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void g(this Selves const&... selves) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -121,7 +121,7 @@ struct S3 {
   void k(this Selves const&...) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
 
   template<typename Selves>
-  void fd(this Selves const&...);
+  void fd(this Selves const&...);	  // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void gd(this Selves const&... selves);  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -136,7 +136,7 @@ struct S3 {
 
 struct S4 {
   template<typename Selves>
-  void f(this Selves const&&...) {}
+  void f(this Selves const&&...) {}	    // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void g(this Selves const&&... selves) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
@@ -149,7 +149,7 @@ struct S4 {
   void k(this Selves const&&...) {}  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
 
   template<typename Selves>
-  void fd(this Selves const&&...);
+  void fd(this Selves const&&...);	   // { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
   template<typename Selves>
   void gd(this Selves const&&... selves);  // { dg-error "an explicit object parameter cannot be a function parameter pack" }
diff --git a/gcc/testsuite/g++.dg/cpp26/variadic-comma1.C b/gcc/testsuite/g++.dg/cpp26/variadic-comma1.C
new file mode 100644
index 0000000..d5cf13f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/variadic-comma1.C
@@ -0,0 +1,18 @@
+// P3176R1 - The Oxford variadic comma
+// { dg-do compile { target c++11 } }
+
+void f1 (int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++26 } }
+#if __cplusplus >= 202002L
+void f2 (auto...);
+void f3 (auto......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++26 } }
+#endif
+template <typename ...T>
+void f4 (T......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++26 } }
+template <typename ...T>
+void f5 (T...);
+template <typename ...T>
+void f6 (T..., int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++26 } }
+void
+f7 (char...)			// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++26 } }
+{
+}
diff --git a/gcc/testsuite/g++.dg/cpp26/variadic-comma2.C b/gcc/testsuite/g++.dg/cpp26/variadic-comma2.C
new file mode 100644
index 0000000..8d2e8f0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/variadic-comma2.C
@@ -0,0 +1,19 @@
+// P3176R1 - The Oxford variadic comma
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wdeprecated" }
+
+void f1 (int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+#if __cplusplus >= 202002L
+void f2 (auto...);
+void f3 (auto......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++20 } }
+#endif
+template <typename ...T>
+void f4 (T......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+template <typename ...T>
+void f5 (T...);
+template <typename ...T>
+void f6 (T..., int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+void
+f7 (char...)			// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+{
+}
diff --git a/gcc/testsuite/g++.dg/cpp26/variadic-comma3.C b/gcc/testsuite/g++.dg/cpp26/variadic-comma3.C
new file mode 100644
index 0000000..6413478
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/variadic-comma3.C
@@ -0,0 +1,5 @@
+// P3176R1 - The Oxford variadic comma
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wno-deprecated-variadic-comma-omission" }
+
+#include "variadic-comma1.C"
diff --git a/gcc/testsuite/g++.dg/cpp26/variadic-comma4.C b/gcc/testsuite/g++.dg/cpp26/variadic-comma4.C
new file mode 100644
index 0000000..12f0d54
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/variadic-comma4.C
@@ -0,0 +1,5 @@
+// P3176R1 - The Oxford variadic comma
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wno-deprecated" }
+
+#include "variadic-comma1.C"
diff --git a/gcc/testsuite/g++.dg/cpp26/variadic-comma5.C b/gcc/testsuite/g++.dg/cpp26/variadic-comma5.C
new file mode 100644
index 0000000..ccf3ebc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/variadic-comma5.C
@@ -0,0 +1,19 @@
+// P3176R1 - The Oxford variadic comma
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wdeprecated-variadic-comma-omission" }
+
+void f1 (int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+#if __cplusplus >= 202002L
+void f2 (auto...);
+void f3 (auto......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" "" { target c++20 } }
+#endif
+template <typename ...T>
+void f4 (T......);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+template <typename ...T>
+void f5 (T...);
+template <typename ...T>
+void f6 (T..., int...);		// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+void
+f7 (char...)			// { dg-warning "omission of ',' before varargs '...' is deprecated in" }
+{
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic10.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic10.C
index 47a87bb..7329fa8 100644
--- a/gcc/testsuite/g++.dg/cpp2a/lambda-generic10.C
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic10.C
@@ -4,7 +4,7 @@
 void sink(...);
 template <int... args> void f()
 {
-  sink ([] <int T> (int...) { return 1; }
+  sink ([] <int T> (int...) { return 1; }	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
         .operator()<args>(args...)...); // { dg-warning "-Wmissing-template-keyword" }
 } // { dg-prune-output {expected '\)'} }
 
diff --git a/gcc/testsuite/g++.dg/ext/attrib33.C b/gcc/testsuite/g++.dg/ext/attrib33.C
index 55bfc4c..a244c1a 100644
--- a/gcc/testsuite/g++.dg/ext/attrib33.C
+++ b/gcc/testsuite/g++.dg/ext/attrib33.C
@@ -5,7 +5,7 @@
 template <int N>
 struct T
 {
-  void foo (char const * ...) __attribute__ ((format (printf,2,3)));
+  void foo (char const * ...) __attribute__ ((format (printf,2,3)));	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 };
 
 template struct T<3>;
diff --git a/gcc/testsuite/g++.old-deja/g++.law/operators15.C b/gcc/testsuite/g++.old-deja/g++.law/operators15.C
index ea0e688..9318f15 100644
--- a/gcc/testsuite/g++.old-deja/g++.law/operators15.C
+++ b/gcc/testsuite/g++.old-deja/g++.law/operators15.C
@@ -6,7 +6,7 @@
 // Subject: bug report
 // Date: Wed, 27 Jan 1993 16:37:30 -0500
 
-extern "C" int printf(const char* ...);
+extern "C" int printf(const char* ...);	// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
 
 int     delete_counter = -1;
 
diff --git a/gcc/testsuite/g++.old-deja/g++.mike/p12306.C b/gcc/testsuite/g++.old-deja/g++.mike/p12306.C
index 6309016..b96be33 100644
--- a/gcc/testsuite/g++.old-deja/g++.mike/p12306.C
+++ b/gcc/testsuite/g++.old-deja/g++.mike/p12306.C
@@ -4,7 +4,7 @@
 void *ptr1, *ptr2;
 int fail = 0;
 
-extern "C" int printf(const char *...);
+extern "C" int printf(const char *, ...);
 
 class RWSlist { };
 
diff --git a/gcc/testsuite/g++.old-deja/g++.mike/p811.C b/gcc/testsuite/g++.old-deja/g++.mike/p811.C
index 174b16e..ee20715 100644
--- a/gcc/testsuite/g++.old-deja/g++.mike/p811.C
+++ b/gcc/testsuite/g++.old-deja/g++.mike/p811.C
@@ -305,7 +305,7 @@ class ostream : public ios
     ostream& seekp(streampos);
     ostream& seekp(streamoff, _seek_dir);
     streampos tellp();
-    ostream& form(const char *format ...);
+    ostream& form(const char *format ...);		// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
     ostream& vform(const char *format, char*  args);
 };
 
@@ -460,7 +460,7 @@ class iostream : public ios {
 	{ return ((ostream*)this)->write((char*)s, n); }
     ostream& write(const void *s, int n)
 	{ return ((ostream*)this)->write((char*)s, n); }
-    ostream& form(const char *format ...);
+    ostream& form(const char *format ...);		// { dg-warning "omission of ',' before varargs '...' is deprecated" "" { target c++26 } }
     ostream& vform(const char *format, char*  args)
 	{ return ((ostream*)this)->vform(format, args); }
     ostream& seekp(streampos pos) { return ((ostream*)this)->seekp(pos); }