* fileio.c (Fwrite_region, Fdo_auto_save): Handle save_length = -2.

(Fset_buffer_auto_saved): Handle save_length = -2.

Comment changes in other files.

4 files changed, 27 insertions, 8 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 999269f60a8..698ab0d58dd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2009-07-16  Richard Stallman  <rms@gnu.org>
+
+        * fileio.c (Fwrite_region, Fdo_auto_save): Handle save_length = -2.
+        (Fset_buffer_auto_saved): Handle save_length = -2.
+
 2009-07-16  Chong Yidong  <cyd@stupidchicken.com>
 
         * xterm.c (Qx_gtk_map_stock): New var.
diff --git a/src/buffer.c b/src/buffer.c
index f06a6c06a92..f811f162ef2 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5853,7 +5853,12 @@ Backing up is done before the first time the file is saved.  */);
   DEFVAR_PER_BUFFER ("buffer-saved-size", &current_buffer->save_length,
                      make_number (Lisp_Int),
                      doc: /* Length of current buffer when last read in, saved or auto-saved.
-0 initially.  */);
+0 initially.
+-1 means auto-saving turned off until next real save.
+
+If you set this to -2, that means don't turn off auto-saving in this buffer
+if its text size shrinks.   If you use `buffer-swap-text' on a buffer,
+you probably should set this to -2 in that buffer.  */);
 
   DEFVAR_PER_BUFFER ("selective-display", &current_buffer->selective_display,
                      Qnil,
diff --git a/src/buffer.h b/src/buffer.h
index 1fb322e3ed9..397b97579e6 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -584,6 +584,9 @@ struct buffer
   /* This isn't really used by the C code, so could be deleted.  */
   Lisp_Object backed_up;
   /* Length of file when last read or saved.
+     -1 means auto saving turned off because buffer shrank a lot.
+     -2 means don't turn off auto saving if buffer shrinks.
+       (That value is used with buffer-swap-text.)
      This is not in the  struct buffer_text
      because it's not used in indirect buffers at all.  */
   Lisp_Object save_length;
diff --git a/src/fileio.c b/src/fileio.c
index bf96b3aa2b1..43872d59472 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4492,7 +4492,8 @@ This calls `write-region-annotate-functions' at the start, and
       if (visiting)
         {
           SAVE_MODIFF = MODIFF;
-          XSETFASTINT (current_buffer->save_length, Z - BEG);
+          if (XINT (current_buffer->save_length) != -2)
+            XSETFASTINT (current_buffer->save_length, Z - BEG);
           current_buffer->filename = visit_file;
         }
       UNGCPRO;
@@ -4703,7 +4704,8 @@ This calls `write-region-annotate-functions' at the start, and
   if (visiting)
     {
       SAVE_MODIFF = MODIFF;
-      XSETFASTINT (current_buffer->save_length, Z - BEG);
+      if (XINT (current_buffer->save_length) != -2)
+        XSETFASTINT (current_buffer->save_length, Z - BEG);
       current_buffer->filename = visit_file;
       update_mode_lines++;
     }
@@ -5307,7 +5309,7 @@ A non-nil CURRENT-ONLY argument means save only current buffer.  */)
             && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b)
             && b->auto_save_modified < BUF_MODIFF (b)
             /* -1 means we've turned off autosaving for a while--see below.  */
-            && XINT (b->save_length) >= 0
+            && XINT (b->save_length) != -1
             && (do_handled_files
                 || NILP (Ffind_file_name_handler (b->auto_save_file_name,
                                                   Qwrite_region))))
@@ -5321,8 +5323,10 @@ A non-nil CURRENT-ONLY argument means save only current buffer.  */)
                 && EMACS_SECS (before_time) - b->auto_save_failure_time < 1200)
               continue;
 
-            if ((XFASTINT (b->save_length) * 10
-                 > (BUF_Z (b) - BUF_BEG (b)) * 13)
+            if (XINT (b->save_length) != -2
+                /* -2 is a magic flag turning off this feature in a buffer.  */
+                && (XFASTINT (b->save_length) * 10
+                    > (BUF_Z (b) - BUF_BEG (b)) * 13)
                 /* A short file is likely to change a large fraction;
                    spare the user annoying messages.  */
                 && XFASTINT (b->save_length) > 5000
@@ -5347,7 +5351,8 @@ A non-nil CURRENT-ONLY argument means save only current buffer.  */)
             internal_condition_case (auto_save_1, Qt, auto_save_error);
             auto_saved++;
             b->auto_save_modified = BUF_MODIFF (b);
-            XSETFASTINT (current_buffer->save_length, Z - BEG);
+            if (XINT (current_buffer->save_length) != -2)
+              XSETFASTINT (current_buffer->save_length, Z - BEG);
             set_buffer_internal (old);
 
             EMACS_GET_TIME (after_time);
@@ -5392,7 +5397,8 @@ No auto-save file will be written until the buffer changes again.  */)
      ()
 {
   current_buffer->auto_save_modified = MODIFF;
-  XSETFASTINT (current_buffer->save_length, Z - BEG);
+  if (XINT (current_buffer->save_length) != -2)
+    XSETFASTINT (current_buffer->save_length, Z - BEG);
   current_buffer->auto_save_failure_time = -1;
   return Qnil;
 }