system-name's returned value can vary

Also, the system-name variable is now obsolete.
Fixes Bug#19438.
* doc/lispref/os.texi (System Environment):
* etc/NEWS: Document this.
* doc/misc/efaq.texi:
(Displaying the current file name in the titlebar):
* lisp/desktop.el (desktop-save-frameset):
* lisp/dnd.el (dnd-get-local-file-uri):
* lisp/gnus/message.el (message-make-fqdn):
* lisp/gnus/nnvirtual.el (nnvirtual-retrieve-headers)
(nnvirtual-update-xref-header):
* lisp/nxml/rng-uri.el (rng-uri-file-name-1):
* lisp/org/org-clock.el (org-clock-save):
* src/filelock.c (current_lock_owner):
* src/xrdb.c (get_environ_db):
* src/xterm.c (same_x_server):
* src/xterm.c (x_term_init):
Prefer (system-name) to system-name, and avoid naming
locals 'system-name'.
* doc/misc/smtpmail.texi (Server workarounds): Fix grammar.
* lisp/startup.el (system-name): Now an obsolete variable.
* src/editfns.c (cached_system_name): New static var.
(init_and_cache_system_name): New function.
(init_editfns, Fsystem_name): Use it.
(syms_of_editfns): Initialize it and Vsystem_name to the same value.
* src/sysdep.c [HAVE_SOCKETS]: Don't include <sys/socket.h>, <netdb.h>.
(h_errno) [TRY_AGAIN && !HAVE_H_ERRNO]: Remove decl.
(init_system_name) [HAVE_SOCKETS]: Don't canonicalize the name.
Don't create a new string if the current value is already correct.

5 files changed, 17 insertions, 16 deletions

diff --git a/lisp/desktop.el b/lisp/desktop.el
index bad0073fbba..bcf038762da 100644
--- a/lisp/desktop.el
+++ b/lisp/desktop.el
@@ -940,7 +940,7 @@ Frames with a non-nil `desktop-dont-save' parameter are not saved."
 	(and desktop-restore-frames
 	     (frameset-save nil
 			    :app desktop--app-id
-			    :name (concat user-login-name "@" system-name)
+			    :name (concat user-login-name "@" (system-name))
 			    :predicate #'desktop--check-dont-save))))
 
 ;;;###autoload
diff --git a/lisp/dnd.el b/lisp/dnd.el
index 73b531dfd16..2b68b025ac1 100644
--- a/lisp/dnd.el
+++ b/lisp/dnd.el
@@ -122,17 +122,18 @@ Return nil if URI is not a local file."
 
   ;; The hostname may be our hostname, in that case, convert to a local
   ;; file.  Otherwise return nil.  TODO:  How about an IP-address as hostname?
-  (let ((hostname (when (string-match "^file://\\([^/]*\\)" uri)
+  (let ((system-name (system-name)))
+    (let ((hostname (when (string-match "^file://\\([^/]*\\)" uri)
 		      (downcase (match-string 1 uri))))
-	(system-name-no-dot
-	 (downcase (if (string-match "^[^\\.]+" system-name)
-		       (match-string 0 system-name)
-		     system-name))))
-    (when (and hostname
-	     (or (string-equal "localhost" hostname)
-		 (string-equal (downcase system-name) hostname)
-		 (string-equal system-name-no-dot hostname)))
-	(concat "file://" (substring uri (+ 7 (length hostname)))))))
+	  (system-name-no-dot
+	   (downcase (if (string-match "^[^\\.]+" system-name)
+			 (match-string 0 system-name)
+		       system-name))))
+      (when (and hostname
+		 (or (string-equal "localhost" hostname)
+		     (string-equal (downcase system-name) hostname)
+		     (string-equal system-name-no-dot hostname)))
+	(concat "file://" (substring uri (+ 7 (length hostname))))))))
 
 (defsubst dnd-unescape-uri (uri)
   (replace-regexp-in-string
diff --git a/lisp/gnus/nnvirtual.el b/lisp/gnus/nnvirtual.el
index f67943a336a..d13b492ddb3 100644
--- a/lisp/gnus/nnvirtual.el
+++ b/lisp/gnus/nnvirtual.el
@@ -151,7 +151,7 @@ component group will show up when you enter the virtual group.")
 		  ;; and clean up the xrefs.
 		  (princ article nntp-server-buffer)
 		  (nnvirtual-update-xref-header cgroup carticle
-						prefix system-name)
+						prefix (system-name))
 		  (forward-line 1))
 		)
 
@@ -393,7 +393,7 @@ component group will show up when you enter the virtual group.")
     (forward-char -1)
     (delete-char 1))
 
-  (insert "Xref: " system-name " " group ":")
+  (insert "Xref: " (system-name) " " group ":")
   (princ article (current-buffer))
   (insert " ")
 
diff --git a/lisp/nxml/rng-uri.el b/lisp/nxml/rng-uri.el
index b93624a4f22..43218ec7c88 100644
--- a/lisp/nxml/rng-uri.el
+++ b/lisp/nxml/rng-uri.el
@@ -85,7 +85,7 @@ Signal an error if URI is not a valid file URL."
 	  ((not (string= (downcase scheme) "file"))
 	   (rng-uri-error "URI `%s' does not use the `file:' scheme" uri)))
     (when (not (member authority
-		       (cons system-name '(nil "" "localhost"))))
+		       (cons (system-name) '(nil "" "localhost"))))
       (rng-uri-error "URI `%s' does not start with `file:///' or `file://localhost/'"
 	     uri))
     (when query
diff --git a/lisp/org/org-clock.el b/lisp/org/org-clock.el
index 51c87892a9c..c9287586e4e 100644
--- a/lisp/org/org-clock.el
+++ b/lisp/org/org-clock.el
@@ -2811,8 +2811,8 @@ The details of what will be saved are regulated by the variable
 	  (delete-region (point-min) (point-max))
 	  ;;Store clock
 	  (insert (format ";; org-persist.el - %s at %s\n"
-			  system-name (format-time-string
-				       (cdr org-time-stamp-formats))))
+			  (system-name) (format-time-string
+					 (cdr org-time-stamp-formats))))
 	  (if (and (memq org-clock-persist '(t clock))
 		   (setq b (org-clocking-buffer))
 		   (setq b (or (buffer-base-buffer b) b))