clang/test/C/C23/n2975.c

// RUN: %clang_cc1 -verify -ffreestanding -Wpre-c2x-compat -std=c2x %s

/* WG14 N2975: partial
 * Relax requirements for va_start
 */

#include <stdarg.h>

void func(...) { // expected-warning {{'...' as the only parameter of a function is incompatible with C standards before C23}}
  // Show that va_start doesn't require the second argument in C23 mode.
  va_list list;
  va_start(list); // expected-warning {{passing only one argument to 'va_start' is incompatible with C standards before C23}}
  va_end(list);

  va_start(list, 1, 2); // expected-error {{too many arguments to function call, expected at most 2, have 3}}
  va_end(list);

  // We didn't change the behavior of __builtin_va_start (and neither did GCC).
  __builtin_va_start(list); // expected-error {{too few arguments to function call, expected 2, have 1}}

  // Verify that the return type of a call to va_start is 'void'.
  _Static_assert(__builtin_types_compatible_p(__typeof__(va_start(list)), void), ""); // expected-warning {{passing only one argument to 'va_start' is incompatible with C standards before C23}}
  _Static_assert(__builtin_types_compatible_p(__typeof__(__builtin_va_start(list, 0)), void), ""); // expected-warning {{passing only one argument to 'va_start' is incompatible with C standards before C23}}
}

// Show that function pointer types also don't need an argument before the
// ellipsis.
typedef void (*fp)(...); // expected-warning {{'...' as the only parameter of a function is incompatible with C standards before C23}}

// Passing something other than the argument before the ... is still not valid.
void diag(int a, int b, ...) {
  va_list list;
  va_start(list, a); // expected-warning {{second argument to 'va_start' is not the last non-variadic parameter}}
  // However, the builtin itself is under no such constraints regarding
  // expanding or evaluating the second argument, so it can still diagnose.
  __builtin_va_start(list, a); // expected-warning {{second argument to 'va_start' is not the last non-variadic parameter}}
  va_end(list);
}

void foo(int a...); // expected-error {{C requires a comma prior to the ellipsis in a variadic function type}}

void use(void) {
  // Demonstrate that we can actually call the variadic function when it has no
  // formal parameters.
  func(1, '2', 3.0, "4");
  func();

  // And that assignment still works as expected.
  fp local = func;

  // ...including conversion errors.
  fp other_local = diag; // expected-error {{incompatible function pointer types initializing 'fp' (aka 'void (*)(...)') with an expression of type 'void (int, int, ...)'}}
}