error: Kill @error_warn

We added @error_warn some two years ago in commit 3ffef1a55ca (error:
add global &error_warn destination).  It has multiple issues:

* error.h's big comment was not updated for it.

* Function contracts were not updated for it.

* ERRP_GUARD() is unaware of @error_warn, and fails to mask it from
  error_prepend() and such.  These crash on @error_warn, as pointed
  out by Akihiko Odaki.

All fixable.  However, after more than two years, we had just of 15
uses, of which the last few patches removed seven as unclean or
otherwise undesirable, adding back five elsewhere.  I didn't look
closely enough at the remaining seven to decide whether they are
desirable or not.

I don't think this feature earns its keep.  Drop it.

Thanks-to: Akihiko  Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20250923091000.3180122-14-armbru@redhat.com>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>

1 files changed, 0 insertions, 6 deletions

diff --git a/include/qapi/error.h b/include/qapi/error.h
index 41e3816380..b16c6303f8 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -534,12 +534,6 @@ static inline void error_propagator_cleanup(ErrorPropagator *prop)
 G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup);
 
 /*
- * Special error destination to warn on error.
- * See error_setg() and error_propagate() for details.
- */
-extern Error *error_warn;
-
-/*
  * Special error destination to abort on error.
  * See error_setg() and error_propagate() for details.
  */