Bug 2056613

gcc-12.0.1-0.8.fc36 gives wrong dangling-pointer warnings (with unreachable code `for(;;)`).


This can be seen when building NetworkManager:
Run `podman run -it --privileged fedora:36`


Then:

```
dnf upgrade -y

dnf install git -y

git clone https://gitlab.freedesktop.org/NetworkManager/NetworkManager.git/
cd NetworkManager

git checkout -B test 47ff99515f0ecbc791851f3c1a1c61fb7efc234c

./contrib/fedora/REQUIRED_PACKAGES

CFLAGS='-O2' ./autogen.sh

make src/libnm-glib-aux/libnm_glib_aux_la-nm-shared-utils.lo
```




Compiler failure:
```
In file included from /usr/include/glib-2.0/glib.h:62,
                 from ./src/libnm-glib-aux/nm-default-glib.h:18,
                 from ./src/libnm-glib-aux/nm-default-glib-i18n-lib.h:13,
                 from src/libnm-glib-aux/nm-shared-utils.c:6:
src/libnm-glib-aux/nm-shared-utils.c: In function ‘nm_utils_parse_inaddr_bin_full’:
src/libnm-glib-aux/nm-shared-utils.c:1145:26: error: dangling pointer to ‘error’ may be used [-Werror=dangling-pointer=]
 1145 |                     error->message);
      |                          ^~
/usr/include/glib-2.0/glib/gmessages.h:343:32: note: in definition of macro ‘g_error’
  343 |                                __VA_ARGS__);         \
      |                                ^~~~~~~~~~~
src/libnm-glib-aux/nm-shared-utils.c:1133:31: note: ‘error’ declared here
 1133 |         gs_free_error GError *error = NULL;
      |                               ^~~~~
/usr/include/glib-2.0/glib/gmessages.h:341:25: error: dangling pointer to ‘addrbin’ may be used [-Werror=dangling-pointer=]
  341 |                         g_log (G_LOG_DOMAIN,         \
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  342 |                                G_LOG_LEVEL_ERROR,    \
      |                                ~~~~~~~~~~~~~~~~~~~~~~~
  343 |                                __VA_ARGS__);         \
      |                                ~~~~~~~~~~~~
src/libnm-glib-aux/nm-shared-utils.c:1141:13: note: in expansion of macro ‘g_error’
 1141 |             g_error("unexpected assertion failure: could parse \"%s\" as %s, but not accepted by "
      |             ^~~~~~~
src/libnm-glib-aux/nm-shared-utils.c:1112:14: note: ‘addrbin’ declared here
 1112 |     NMIPAddr addrbin;
      |              ^~~~~~~
cc1: all warnings being treated as errors
```

which happens here: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/47ff99515f0ecbc791851f3c1a1c61fb7efc234c/src/libnm-glib-aux/nm-shared-utils.c#L1141



There are several other failures. Just type `make` in above reproducer.



They are related to glib's `g_error()` macro, which is defined here: https://gitlab.gnome.org/GNOME/glib/-/blob/60e8b48be9f2c1cc3f8212ebfaee58f0750a2754/glib/gmessages.h#L344

```
#define g_error(...)  G_STMT_START {                 \
                        g_log (G_LOG_DOMAIN,         \
                               G_LOG_LEVEL_ERROR,    \
                               __VA_ARGS__);         \
                        for (;;) ;                   \
                      } G_STMT_END
```

The `for(;;)` trips gcc up.