clang/test/C/C2x/n2975.c

   1 // RUN: %clang_cc1 -verify -ffreestanding -Wpre-c2x-compat -std=c2x %s
   2
   3 /* WG14 N2975: partial
   4  * Relax requirements for va_start
   5  */
   6
   7 #include <stdarg.h>
   8
   9 #define DERP this is an error
  10
  11 void func(...) { // expected-warning {{'...' as the only parameter of a function is incompatible with C standards before C2x}}
  12   // Show that va_start doesn't require the second argument in C2x mode.
  13   va_list list;
  14   va_start(list); // FIXME: it would be nice to issue a portability warning to C17 and earlier here.
  15   va_end(list);
  16
  17   // Show that va_start doesn't expand or evaluate the second argument.
  18   va_start(list, DERP);
  19   va_end(list);
  20
  21   // FIXME: it would be kinder to diagnose this instead of silently accepting it.
  22   va_start(list, 1, 2);
  23   va_end(list);
  24
  25   // We didn't change the behavior of __builtin_va_start (and neither did GCC).
  26   __builtin_va_start(list); // expected-error {{too few arguments to function call, expected 2, have 1}}
  27
  28   // Verify that the return type of a call to va_start is 'void'.
  29   _Static_assert(__builtin_types_compatible_p(__typeof__(va_start(list)), void), "");
  30   _Static_assert(__builtin_types_compatible_p(__typeof__(__builtin_va_start(list, 0)), void), "");
  31 }
  32
  33 // Show that function pointer types also don't need an argument before the
  34 // ellipsis.
  35 typedef void (*fp)(...); // expected-warning {{'...' as the only parameter of a function is incompatible with C standards before C2x}}
  36
  37 // Passing something other than the argument before the ... is still not valid.
  38 void diag(int a, int b, ...) {
  39   va_list list;
  40   // FIXME: the call to va_start should also diagnose the same way as the call
  41   // to __builtin_va_start. However, because va_start is not allowed to expand
  42   // or evaluate the second argument, we can't pass it along to
  43   // __builtin_va_start to get that diagnostic. So in C17 and earlier, we will
  44   // diagnose this use through the macro, but in C2x and later we've lost the
  45   // diagnostic entirely. GCC has the same issue currently.
  46   va_start(list, a);
  47   // However, the builtin itself is under no such constraints regarding
  48   // expanding or evaluating the second argument, so it can still diagnose.
  49   __builtin_va_start(list, a); // expected-warning {{second argument to 'va_start' is not the last named parameter}}
  50   va_end(list);
  51 }
  52
  53 void foo(int a...); // expected-error {{C requires a comma prior to the ellipsis in a variadic function type}}
  54
  55 void use(void) {
  56   // Demonstrate that we can actually call the variadic function when it has no
  57   // formal parameters.
  58   func(1, '2', 3.0, "4");
  59   func();
  60
  61   // And that assignment still works as expected.
  62   fp local = func;
  63
  64   // ...including conversion errors.
  65   fp other_local = diag; // expected-error {{incompatible function pointer types initializing 'fp' (aka 'void (*)(...)') with an expression of type 'void (int, int, ...)'}}
  66 }