emacsclient: prefer XDG_RUNTIME_DIR (Bug#33367)

* lib-src/emacsclient.c: Disable -Wformat-truncation=2,
to avoid false alarms about the new snprintf calls.
(local_sockname): New function.
(set_local_socket): Use it.  Prefer XDG_RUNTIME_DIR (if set)
for location of socket directory.  Avoid unnecessary memory
allocation by using snprintf to destination.
* lisp/server.el (server-socket-dir): Prefer XDG_RUNTIME_DIR if set.

1 files changed, 4 insertions, 2 deletions

diff --git a/doc/misc/efaq.texi b/doc/misc/efaq.texi
index 0d4e4ba8bdd..d457267c248 100644
--- a/doc/misc/efaq.texi
+++ b/doc/misc/efaq.texi
@@ -2005,8 +2005,10 @@ or by invoking @code{server-start} from @file{.emacs}:
 (if (@var{some conditions are met}) (server-start))
 @end lisp
 
-When this is done, Emacs creates a Unix domain socket named
-@file{server} in @file{/tmp/emacs@var{userid}}. See
+When this is done, Emacs by default creates a Unix domain socket named
+@file{server} in a well-known directory, typically
+@file{$XDG_RUNTIME_DIR/emacs} if Emacs is running under an X Window System
+desktop and @file{$TMPDIR/emacs@var{userid}} otherwise.  See the variable
 @code{server-socket-dir}.
 
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