bad interaction between set-buffer-multibyte and narrowing

bad interaction between set-buffer-multibyte and narrowing

[Dave Love]

This is cut down from a real example in a Gnus bug report.  Note how
the buffer-string is truncated.

Making the buffer unibyte leaves point-max unchanged and it gets
reduced when the buffer is made multibyte again.  You can see this by
just making a narrowed buffer unibyte which contains Japanese.  The
effect is present in both the released and development code.

(with-temp-buffer
  (insert "From: ニシキノネット　FC事業部
Content-Type: text/plain; charset=ISO-2022-JP\n\n")
  (narrow-to-region (point-min) (1- (point-max)))
  (set-buffer-multibyte nil)
  (set-buffer-multibyte t)
  (buffer-string))
  => "From: ニシキノネット　FC事業部
Content-Type: text/plain"

Re: bad interaction between set-buffer-multibyte and narrowing

[Kenichi Handa]

In article <rzqsmqw5oqg.fsf@albion.dl.ac.uk>, Dave Love <d.love@dl.ac.uk> writes:
> This is cut down from a real example in a Gnus bug report.
> Note how the buffer-string is truncated.

> Making the buffer unibyte leaves point-max unchanged and
> it gets reduced when the buffer is made multibyte again.
> You can see this by just making a narrowed buffer unibyte
> which contains Japanese.  The effect is present in both
> the released and development code.

> (with-temp-buffer (insert "From: ニシキノネット　FC事業部
> Content-Type: text/plain; charset=ISO-2022-JP\n\n")
> (narrow-to-region (point-min) (1- (point-max)))
> (set-buffer-multibyte nil) (set-buffer-multibyte t)
> (buffer-string)) => "From: ニシキノネット　FC事業部
> Content-Type: text/plain"

Thank you for the report.  I've just installed the attached
fix in HEAD and RC.

---
Ken'ichi HANDA
handa@m17n.org

2003-05-31  Kenichi Handa  <handa@m17n.org>

	* buffer.c (Fset_buffer_multibyte): Correctly recover a narrowed
	region when a buffer is changed to unibyte.

Index: buffer.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/buffer.c,v
retrieving revision 1.423
retrieving revision 1.424
diff -u -c -r1.423 -r1.424
cvs server: conflicting specifications of output style
*** buffer.c	29 May 2003 18:36:07 -0000	1.423
--- buffer.c	1 Jun 2003 23:27:34 -0000	1.424
***************
*** 2049,2055 ****
    Lisp_Object tail, markers;
    struct buffer *other;
    int undo_enabled_p = !EQ (current_buffer->undo_list, Qt);
!   int begv = BEGV, zv = ZV;
    int narrowed = (BEG != begv || Z != zv);
    int modified_p = !NILP (Fbuffer_modified_p (Qnil));
  
--- 2049,2055 ----
    Lisp_Object tail, markers;
    struct buffer *other;
    int undo_enabled_p = !EQ (current_buffer->undo_list, Qt);
!   int begv, zv;
    int narrowed = (BEG != begv || Z != zv);
    int modified_p = !NILP (Fbuffer_modified_p (Qnil));
  
***************
*** 2067,2072 ****
--- 2067,2077 ----
  
    /* If the cached position is for this buffer, clear it out.  */
    clear_charpos_cache (current_buffer);
+ 
+   if (NILP (flag))
+     begv = BEGV_BYTE, zv = ZV_BYTE;
+   else
+     begv = BEGV, zv = ZV;
  
    if (narrowed)
      Fwiden ();