build: Define DBUS_INT64_MODIFIER, analogous to G_GINT64_MODIFIER

Using PRId64, etc. to print dbus_int64_t or dbus_uint64_t is not 100%
portable. On platforms where both long and long long are 64-bit (such as
Linux and macOS), we will prefer to define dbus_int64_t as long.
If the operating system has chosen to define int64_t as long long,
which is apparently the case on macOS, then the compiler can warn that
we are passing a long argument to PRId64, which is "lld" and therefore
expects a long long argument (even though that ends up with the same
bit-pattern being used).

We can't necessarily just use int64_t and uint64_t directly, even if all
our supported platforms have them available now, because swapping
dbus_int64_t between long and long long might change C++ name mangling,
causing ABI breaks in third-party libraries if they define C++ functions
that take a dbus_int64_t argument.

Signed-off-by: Simon McVittie <smcv@collabora.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/bus/containers.c b/bus/containers.c
index 8abeca1f..1a95a4a5 100644
--- a/bus/containers.c
+++ b/bus/containers.c
@@ -414,10 +414,8 @@ bus_container_instance_new (BusContext *context,
       goto fail;
     }
 
-  /* We assume PRIu64 exists on all Unix platforms: it's ISO C99, and the
-   * only non-C99 platform we support is MSVC on Windows. */
   if (!_dbus_string_append_printf (&path,
-                                   "/org/freedesktop/DBus/Containers1/c%" PRIu64,
+                                   "/org/freedesktop/DBus/Containers1/c%" DBUS_INT64_MODIFIER "u",
                                    containers->next_container_id++))
     {
       BUS_SET_OOM (error);