Add support in emacsclient for EMACS_SOCKET_NAME

If the '--socket-name' argument is unspecified, the environment
variable 'EMACS_SOCKET_NAME' is now consulted with the same
semantics.  This mirrors the behavior of the '--server-file' argument,
and allows for easier configuration of emacsclient when the socket is
in a location other than 'TMPDIR' or '/tmp'.

* emacsclient.c (set_socket): Add support for the
EMACS_SOCKET_NAME environment variable.  (Bug#33095)

* misc.texi (emacsclient Options):
* emacsclient.1: Document the EMACS_SOCKET_NAME environment
variable.

* etc/NEWS: Announce the new feature.

Copyright-paperwork-exempt: yes

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 2249aa48ab8..be32ac6b9bb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -120,6 +120,12 @@ the new version of the file again.)
 * Changes in Emacs 27.1
 
 +++
+** emacsclient uses EMACS_SOCKET_NAME if --socket-name is not set.
+The behavior is identical to the EMACS_SERVER_FILE, in that the
+command line value will override the environment, and the natural
+default to TMPDIR, then /tmp, continues to apply.
+
++++
 ** The function 'read-passwd' uses '*' as default character to hide passwords.
 
 ---