Reduce delay between backing up a file and saving new version

* lisp/files.el (basic-save-buffer-2):
Choose coding system for writing the file before backing it up.

* src/fileio.c (choose_write_coding_system): Make it callable from Lisp.
(Fwrite_region): If coding-system-for-write is set, don't call
choose_write_coding_system.
Move the last piece of choose_write_coding_system here.
(syms_of_fileio): Add choose-write-coding-system.

Fixes: debbugs:13522

lisp/ChangeLog

@@ -1,3 +1,9 @@
+2013-01-31  Glenn Morris  <rgm@gnu.org>
+
+	* files.el (basic-save-buffer-2): Choose coding system for
+	writing the file before backing it up, to reduce delay between
+	backing up and writing the new version.  (Bug#13522)
+
 2013-01-31  Michal Nazarewicz  <mina86@mina86.com>
 
 	* simple.el (cycle-spacing): New command.

lisp/files.el

@@ -4656,7 +4656,7 @@ Before and after saving the buffer, this function runs
 ;; This returns a value (MODES EXTENDED-ATTRIBUTES BACKUPNAME), like
 ;; backup-buffer.
 (defun basic-save-buffer-2 ()
-  (let (tempsetmodes setmodes)
+  (let (tempsetmodes setmodes writecoding)
     (if (not (file-writable-p buffer-file-name))
 	(let ((dir (file-name-directory buffer-file-name)))
 	  (if (not (file-directory-p dir))
@@ -4672,6 +4672,14 @@ Before and after saving the buffer, this function runs
 		     buffer-file-name)))
 		  (setq tempsetmodes t)
 		(error "Attempt to save to a file which you aren't allowed to write"))))))
+    ;; This may involve prompting, so do it now before backing up the file.
+    ;; Otherwise there can be a delay while the user answers the
+    ;; prompt during which the original file has been renamed.  (Bug#13522)
+    (setq writecoding
+	  ;; Args here should match write-region call below around
+	  ;; which we use writecoding.
+	  (choose-write-coding-system nil nil buffer-file-name nil t
+				      buffer-file-truename))
     (or buffer-backed-up
 	(setq setmodes (backup-buffer)))
     (let* ((dir (file-name-directory buffer-file-name))
@@ -4753,10 +4761,11 @@ Before and after saving the buffer, this function runs
 				 (logior (car setmodes) 128))))))
 	(let (success)
 	  (unwind-protect
-	      (progn
                 ;; Pass in nil&nil rather than point-min&max to indicate
                 ;; we're saving the buffer rather than just a region.
                 ;; write-region-annotate-functions may make us of it.
+	      (let ((coding-system-for-write writecoding)
+		    (coding-system-require-warning nil))
 		(write-region nil nil
 			      buffer-file-name nil t buffer-file-truename)
 		(setq success t))

src/ChangeLog

@@ -1,3 +1,11 @@
+2013-01-31  Glenn Morris  <rgm@gnu.org>
+
+	* fileio.c (choose_write_coding_system): Make it callable from Lisp.
+	(Fwrite_region): If coding-system-for-write is set, don't
+	call choose_write_coding_system.  Move the last piece of
+	choose_write_coding_system here.  (Bug#13522)
+	(syms_of_fileio): Add choose-write-coding-system.
+
 2013-01-30  Eli Zaretskii  <eliz@gnu.org>
 
 	* w32.c (sys_open): Zero out the flags for the new file descriptor.

src/fileio.c

@@ -249,6 +249,7 @@ static Lisp_Object Qfile_acl;
 static Lisp_Object Qset_file_acl;
 static Lisp_Object Qfile_newer_than_file_p;
 Lisp_Object Qinsert_file_contents;
+Lisp_Object Qchoose_write_coding_system;
 Lisp_Object Qwrite_region;
 static Lisp_Object Qverify_visited_file_modtime;
 static Lisp_Object Qset_visited_file_modtime;
@@ -4615,14 +4616,24 @@ build_annotations_unwind (Lisp_Object arg)
 
 /* Decide the coding-system to encode the data with.  */
 
-static Lisp_Object
+DEFUN ("choose-write-coding-system", Fchoose_write_coding_system,
-choose_write_coding_system (Lisp_Object start, Lisp_Object end, Lisp_Object filename,
+       Schoose_write_coding_system, 3, 6, 0,
-			    Lisp_Object append, Lisp_Object visit, Lisp_Object lockname,
+       doc: /* Choose the coding system for writing a file.
-			    struct coding_system *coding)
+Arguments are as for `write-region'.
+This function is for internal use only.  It may prompt the user.  */ )
+  (Lisp_Object start, Lisp_Object end, Lisp_Object filename,
+   Lisp_Object append, Lisp_Object visit, Lisp_Object lockname)
 {
   Lisp_Object val;
   Lisp_Object eol_parent = Qnil;
 
+  /* Mimic write-region behavior.  */
+  if (NILP (start))
+    {
+      XSETFASTINT (start, BEGV);
+      XSETFASTINT (end, ZV);
+    }
+
   if (auto_saving
       && NILP (Fstring_equal (BVAR (current_buffer, filename),
 			      BVAR (current_buffer, auto_save_file_name))))
@@ -4715,10 +4726,6 @@ choose_write_coding_system (Lisp_Object start, Lisp_Object end, Lisp_Object file
     }
 
   val = coding_inherit_eol_type (val, eol_parent);
-  setup_coding_system (val, coding);
-
-  if (!STRINGP (start) && !NILP (BVAR (current_buffer, selective_display)))
-    coding->mode |= CODING_MODE_SELECTIVE_DISPLAY;
   return val;
 }
 
@@ -4874,9 +4881,15 @@ This calls `write-region-annotate-functions' at the start, and
      We used to make this choice before calling build_annotations, but that
      leads to problems when a write-annotate-function takes care of
      unsavable chars (as was the case with X-Symbol).  */
-  Vlast_coding_system_used
+  Vlast_coding_system_used = NILP (Vcoding_system_for_write) ?
-    = choose_write_coding_system (start, end, filename,
+    Fchoose_write_coding_system (start, end, filename,
-				  append, visit, lockname, &coding);
+                                append, visit, lockname) :
+    Vcoding_system_for_write;
+
+  setup_coding_system (Vlast_coding_system_used, &coding);
+
+  if (!STRINGP (start) && !NILP (BVAR (current_buffer, selective_display)))
+    coding.mode |= CODING_MODE_SELECTIVE_DISPLAY;
 
 #ifdef CLASH_DETECTION
   if (!auto_saving)
@@ -5861,6 +5874,7 @@ syms_of_fileio (void)
   DEFSYM (Qset_file_acl, "set-file-acl");
   DEFSYM (Qfile_newer_than_file_p, "file-newer-than-file-p");
   DEFSYM (Qinsert_file_contents, "insert-file-contents");
+  DEFSYM (Qchoose_write_coding_system, "choose-write-coding-system");
   DEFSYM (Qwrite_region, "write-region");
   DEFSYM (Qverify_visited_file_modtime, "verify-visited-file-modtime");
   DEFSYM (Qset_visited_file_modtime, "set-visited-file-modtime");
@@ -6085,6 +6099,7 @@ This includes interactive calls to `delete-file' and
   defsubr (&Sdefault_file_modes);
   defsubr (&Sfile_newer_than_file_p);
   defsubr (&Sinsert_file_contents);
+  defsubr (&Schoose_write_coding_system);
   defsubr (&Swrite_region);
   defsubr (&Scar_less_than_car);
   defsubr (&Sverify_visited_file_modtime);