DBusString: Add _DBUS_STRING_INIT_INVALID and allow "freeing" it

This means we can finally use patterns like this:

      DBusString buffer = _DBUS_STRING_INIT_INVALID;
      dbus_bool_t ret = FALSE;

      ... some long setup ...

      if (!_dbus_string_init (&buffer))
        goto out;

      ... some long operation ...

      ret = TRUE;

    out:
      ... free things ...
      _dbus_string_free (&buffer);
      ... free more things ...
      return ret;

without having to have a separate boolean to track whether buffer has
been initialized.

One observable difference is that if s is a "const" (borrowed pointer)
string, _dbus_string_free (&s) now sets it to be invalid. Previously,
it would have kept its (borrowed pointer) contents, which seems like
a violation of least-astonishment.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=89104

1 files changed, 9 insertions, 1 deletions

diff --git a/dbus/dbus-string-util.c b/dbus/dbus-string-util.c
index 08e0e917..a1390fea 100644
--- a/dbus/dbus-string-util.c
+++ b/dbus/dbus-string-util.c
@@ -228,7 +228,7 @@ _DBUS_STRING_DEFINE_STATIC (test_static_string, "hello");
 dbus_bool_t
 _dbus_string_test (void)
 {
-  DBusString str;
+  DBusString str = _DBUS_STRING_INIT_INVALID;
   DBusString other;
   int i, a, end;
   long v;
@@ -245,6 +245,11 @@ _dbus_string_test (void)
   _dbus_assert (real_test_static_string->valid);
   _dbus_assert (real_test_static_string->align_offset == 0);
 
+  /* Test that _DBUS_STRING_INIT_INVALID has the desired effect */
+  _dbus_string_free (&str);
+  _dbus_string_free (&str);
+  _dbus_string_free (&str);
+
   /* Test shortening and setting length */
   i = 0;
   while (i < _DBUS_N_ELEMENTS (lens))
@@ -270,6 +275,9 @@ _dbus_string_test (void)
         }
       
       _dbus_string_free (&str);
+      /* Test that a cleared string is effectively _DBUS_STRING_INIT_INVALID */
+      _dbus_string_free (&str);
+      _dbus_string_free (&str);
 
       ++i;
     }