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, 41 insertions, 22 deletions

diff --git a/src/editfns.c b/src/editfns.c
index 430c4c91fb3..2a7dd9209ae 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -93,6 +93,17 @@ static char const *initial_tz;
    It is OK (though a bit slower) if the user chooses this value.  */
 static char dump_tz_string[] = "TZ=UtC0";
 
+/* The cached value of Vsystem_name.  This is used only to compare it
+   to Vsystem_name, so it need not be visible to the GC.  */
+static Lisp_Object cached_system_name;
+
+static void
+init_and_cache_system_name (void)
+{
+  init_system_name ();
+  cached_system_name = Vsystem_name;
+}
+
 void
 init_editfns (void)
 {
@@ -102,7 +113,7 @@ init_editfns (void)
   Lisp_Object tem;
 
   /* Set up system_name even when dumping.  */
-  init_system_name ();
+  init_and_cache_system_name ();
 
 #ifndef CANNOT_DUMP
   /* When just dumping out, set the time zone to a known unlikely value
@@ -1365,6 +1376,8 @@ DEFUN ("system-name", Fsystem_name, Ssystem_name, 0, 0, 0,
        doc: /* Return the host name of the machine you are running on, as a string.  */)
   (void)
 {
+  if (EQ (Vsystem_name, cached_system_name))
+    init_and_cache_system_name ();
   return Vsystem_name;
 }
 
@@ -4965,6 +4978,7 @@ functions if all the text being accessed has this property.  */);
 
   DEFVAR_LISP ("system-name", Vsystem_name,
 	       doc: /* The host name of the machine Emacs is running on.  */);
+  Vsystem_name = cached_system_name = Qnil;
 
   DEFVAR_LISP ("user-full-name", Vuser_full_name,
 	       doc: /* The full name of the user logged in.  */);
diff --git a/src/filelock.c b/src/filelock.c
index f857c488143..99215f215e7 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -592,9 +592,10 @@ current_lock_owner (lock_info_type *owner, char *lfname)
     return -1;
 
   /* On current host?  */
-  if (STRINGP (Vsystem_name)
-      && dot - (at + 1) == SBYTES (Vsystem_name)
-      && memcmp (at + 1, SSDATA (Vsystem_name), SBYTES (Vsystem_name)) == 0)
+  Lisp_Object system_name = Fsystem_name ();
+  if (STRINGP (system_name)
+      && dot - (at + 1) == SBYTES (system_name)
+      && memcmp (at + 1, SSDATA (system_name), SBYTES (system_name)) == 0)
     {
       if (pid == getpid ())
         ret = 2; /* We own it.  */
diff --git a/src/sysdep.c b/src/sysdep.c
index 24cc5cb0b40..b4a9be1eb1a 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -1420,15 +1420,16 @@ extern int h_errno;
 void
 init_system_name (void)
 {
+  char *hostname_alloc = NULL;
+  char *hostname;
 #ifndef HAVE_GETHOSTNAME
   struct utsname uts;
   uname (&uts);
-  Vsystem_name = build_string (uts.nodename);
+  hostname = uts.nodename;
 #else /* HAVE_GETHOSTNAME */
-  char *hostname_alloc = NULL;
   char hostname_buf[256];
   ptrdiff_t hostname_size = sizeof hostname_buf;
-  char *hostname = hostname_buf;
+  hostname = hostname_buf;
 
   /* Try to get the host name; if the buffer is too short, try
      again.  Apparently, the only indication gethostname gives of
@@ -1541,15 +1542,15 @@ init_system_name (void)
 #endif /* !HAVE_GETADDRINFO */
       }
 #endif /* HAVE_SOCKETS */
-  Vsystem_name = build_string (hostname);
-  xfree (hostname_alloc);
 #endif /* HAVE_GETHOSTNAME */
-  {
-    char *p;
-    for (p = SSDATA (Vsystem_name); *p; p++)
-      if (*p == ' ' || *p == '\t')
-	*p = '-';
-  }
+  char *p;
+  for (p = hostname; *p; p++)
+    if (*p == ' ' || *p == '\t')
+      *p = '-';
+  if (! (STRINGP (Vsystem_name) && SBYTES (Vsystem_name) == p - hostname
+	 && strcmp (SSDATA (Vsystem_name), hostname) == 0))
+    Vsystem_name = build_string (hostname);
+  xfree (hostname_alloc);
 }
 
 sigset_t empty_mask;
diff --git a/src/xrdb.c b/src/xrdb.c
index e21206d0800..8500fb1095b 100644
--- a/src/xrdb.c
+++ b/src/xrdb.c
@@ -385,10 +385,11 @@ get_environ_db (void)
     {
       char *home = gethomedir ();
       ptrdiff_t homelen = strlen (home);
+      Lisp_Object system_name = Fsystem_name ();
       ptrdiff_t filenamesize = (homelen + sizeof xdefaults
-				+ SBYTES (Vsystem_name));
+				+ SBYTES (system_name));
       p = filename = xrealloc (home, filenamesize);
-      lispstpcpy (stpcpy (filename + homelen, xdefaults), Vsystem_name);
+      lispstpcpy (stpcpy (filename + homelen, xdefaults), system_name);
     }
 
   db = XrmGetFileDatabase (p);
diff --git a/src/xterm.c b/src/xterm.c
index 130174dff19..892562bd612 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -10497,8 +10497,9 @@ static bool
 same_x_server (const char *name1, const char *name2)
 {
   bool seen_colon = false;
-  const char *system_name = SSDATA (Vsystem_name);
-  ptrdiff_t system_name_length = SBYTES (Vsystem_name);
+  Lisp_Object sysname = Fsystem_name ();
+  const char *system_name = SSDATA (sysname);
+  ptrdiff_t system_name_length = SBYTES (sysname);
   ptrdiff_t length_until_period = 0;
 
   while (system_name[length_until_period] != 0
@@ -10890,14 +10891,15 @@ x_term_init (Lisp_Object display_name, char *xrm_option, char *resource_name)
 #endif
 
   lim = min (PTRDIFF_MAX, SIZE_MAX) - sizeof "@";
-  if (lim - SBYTES (Vinvocation_name) < SBYTES (Vsystem_name))
+  Lisp_Object system_name = Fsystem_name ();
+  if (lim - SBYTES (Vinvocation_name) < SBYTES (system_name))
     memory_full (SIZE_MAX);
   dpyinfo->x_id = ++x_display_id;
   dpyinfo->x_id_name = xmalloc (SBYTES (Vinvocation_name)
-				+ SBYTES (Vsystem_name) + 2);
+				+ SBYTES (system_name) + 2);
   char *nametail = lispstpcpy (dpyinfo->x_id_name, Vinvocation_name);
   *nametail++ = '@';
-  lispstpcpy (nametail, Vsystem_name);
+  lispstpcpy (nametail, system_name);
 
   /* Figure out which modifier bits mean what.  */
   x_find_modifier_meanings (dpyinfo);