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

2 files changed, 17 insertions, 2 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 6ac51724328..c1142a45e8d 100644
--- a/lisp/ChangeLog
+++ b/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.
diff --git a/lisp/files.el b/lisp/files.el
index b015b53db3c..3bc3059c68f 100644
--- a/lisp/files.el
+++ b/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))