opaque types and ASSERT_EQ

[Gottox]

Thanks a lot for this library! I have found it quite helpful!

Nonetheless, I'm facing the issue, that I have problems when I do NULL checks for opaque types:

#include "utest.h"

struct Foo;

UTEST(a, b) {
	struct Foo *foo = NULL;
	ASSERT_EQ(NULL, foo);
}

UTEST_MAIN();

clang-17 works here, but if I compile with gcc-13 I get the following error:

In file included from t.c:1:
t.c: In function 'utest_run_a_b':
utest.h:678:36: error: invalid use of undefined type 'struct Foo'
  678 | #define UTEST_AUTO(x) __typeof__(x + 0)
      |                                    ^
utest.h:754:5: note: in expansion of macro 'UTEST_AUTO'
  754 |     UTEST_AUTO(y) yEval = (y);                                                 \
      |     ^~~~~~~~~~
utest.h:800:25: note: in expansion of macro 'UTEST_COND'
  800 | #define ASSERT_EQ(x, y) UTEST_COND(x, y, ==, "", 1)
      |                         ^~~~~~~~~~
t.c:7:9: note: in expansion of macro 'ASSERT_EQ'
    7 |         ASSERT_EQ(NULL, foo);
      |         ^~~~~~~~~
utest.h:643:41: error: arithmetic on pointer to an incomplete type
  643 |                         : _Generic((val - val), ptrdiff_t                      \
      |                                         ^
utest.h:405:33: note: in definition of macro 'UTEST_PRINTF'
  405 |     fprintf(utest_state.output, __VA_ARGS__);                                  \
      |                                 ^~~~~~~~~~~
utest.h:765:7: note: in expansion of macro 'utest_type_printer'
  765 |       utest_type_printer(yEval);                                               \
      |       ^~~~~~~~~~~~~~~~~~
utest.h:800:25: note: in expansion of macro 'UTEST_COND'
  800 | #define ASSERT_EQ(x, y) UTEST_COND(x, y, ==, "", 1)
      |                         ^~~~~~~~~~
t.c:7:9: note: in expansion of macro 'ASSERT_EQ'
    7 |         ASSERT_EQ(NULL, foo);
      |         ^~~~~~~~~
utest.h:643:41: error: arithmetic on pointer to an incomplete type
  643 |                         : _Generic((val - val), ptrdiff_t                      \
      |                                         ^
utest.h:407:10: note: in definition of macro 'UTEST_PRINTF'
  407 |   printf(__VA_ARGS__)
      |          ^~~~~~~~~~~
utest.h:765:7: note: in expansion of macro 'utest_type_printer'
  765 |       utest_type_printer(yEval);                                               \
      |       ^~~~~~~~~~~~~~~~~~
utest.h:800:25: note: in expansion of macro 'UTEST_COND'
  800 | #define ASSERT_EQ(x, y) UTEST_COND(x, y, ==, "", 1)
      |                         ^~~~~~~~~~
t.c:7:9: note: in expansion of macro 'ASSERT_EQ'
    7 |         ASSERT_EQ(NULL, foo);
      |         ^~~~~~~~~

[Gottox]

Out of curiousity: why is typeof(x + 0) instead of typeof(x) used here?