Hi!
While the non-comma variadic functions/methods were deprecated in C++26,
they are still valid and they are valid without deprecation in C++98 to
C++23.
We parse default arguments followed by ...) outside of classes or
for out of class definitions of methods, but I think since C++11 support
in GCC 4.9 or so we consider ... to be a part of a default argument and
error on it.
I think a default argument can't validly contain a pack expansion
that ends the expression with ..., so I think we can simply handle
...) if at depth 0 as not part of the default argument.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-08-14 Jakub Jelinek <ja...@redhat.com>
PR c++/121539
* parser.cc (cp_parser_cache_defarg): Set done to true for
CPP_ELLIPSIS followed by CPP_CLOSE_PAREN in !nsdmi at depth 0.
* g++.dg/parse/defarg20.C: New test.
--- gcc/cp/parser.cc.jj 2025-08-13 22:10:18.000000000 +0200
+++ gcc/cp/parser.cc 2025-08-14 11:06:11.999673171 +0200
@@ -37080,7 +37080,11 @@ cp_parser_cache_defarg (cp_parser *parse
case CPP_CLOSE_SQUARE:
if (depth == 0
/* Handle correctly int n = sizeof ... ( p ); */
- && token->type != CPP_ELLIPSIS)
+ && (token->type != CPP_ELLIPSIS
+ /* For int n = 42 ...) handle ... as variadic arguments. */
+ || (!nsdmi
+ && cp_lexer_nth_token_is (parser->lexer, 2,
+ CPP_CLOSE_PAREN))))
done = true;
/* Update DEPTH, if necessary. */
else if (token->type == CPP_CLOSE_PAREN
--- gcc/testsuite/g++.dg/parse/defarg20.C.jj 2025-08-14 11:40:01.787894274
+0200
+++ gcc/testsuite/g++.dg/parse/defarg20.C 2025-08-14 11:44:59.157122997
+0200
@@ -0,0 +1,79 @@
+// PR c++/121539
+// { dg-do run }
+
+#include <cstdarg>
+
+#if __cplusplus >= 201103L
+#define I {}
+#else
+#define I 0
+#endif
+
+void foo (int = I...); // { dg-warning "omission of
',' before varargs '...' is deprecated" "" { target c++26 } }
+struct S {
+ void foo (int = I...); // { dg-warning "omission of
',' before varargs '...' is deprecated" "" { target c++26 } }
+ void bar (int...); // { dg-warning "omission of
',' before varargs '...' is deprecated" "" { target c++26 } }
+};
+
+void
+foo (int a, ...)
+{
+ if (a == 42)
+ {
+ va_list ap;
+ va_start (ap, a);
+ if (va_arg (ap, double) != 15.0)
+ __builtin_abort ();
+ va_end (ap);
+ }
+ else if (a != 0)
+ __builtin_abort ();
+}
+
+void
+S::foo (int a, ...)
+{
+ if (a == 43)
+ {
+ va_list ap;
+ va_start (ap, a);
+ if (va_arg (ap, double) != 16.0)
+ __builtin_abort ();
+ va_end (ap);
+ }
+ else if (a != 0)
+ __builtin_abort ();
+}
+
+void
+S::bar (int a = I...) // { dg-warning "omission of
',' before varargs '...' is deprecated" "" { target c++26 } }
+{
+ if (a == 44)
+ {
+ va_list ap;
+ va_start (ap, a);
+ if (va_arg (ap, double) != 17.0)
+ __builtin_abort ();
+ va_end (ap);
+ }
+ else if (a != 0)
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ S s;
+ foo ();
+ foo (0);
+ foo (42, 15.0);
+ foo (42, 15.0, 128LL);
+ s.foo ();
+ s.foo (0);
+ s.foo (43, 16.0);
+ s.foo (43, 16.0, 129ULL);
+ s.bar ();
+ s.bar (0);
+ s.bar (44, 17.0);
+ s.bar (44, 17.0, 130L);
+}
Jakub
