major mode falsely changed when writing files

[Frank Schimmel]

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In GNU Emacs 21.1.2 (sparc-sun-solaris2.8, X toolkit, Xaw3d scroll bars)
 of 2002-02-11 on palpatine
configured using `configure  --prefix=/sw/solaris8/emacs-21.1 
--with-x-toolkit=athena --x-includes=/usr/openwin/include 
--x-libraries=/usr/openwin/lib --with-xpm --with-jpeg --with-tiff --with-gif 
--with-png'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: en_US.ISO8859-1
  value of $LC_CTYPE: en_US.ISO8859-1
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: en_US.ISO8859-1
  value of $LC_NUMERIC: en_US.ISO8859-1
  value of $LC_TIME: en_US.ISO8859-1
  value of $LANG: en_US.ISO8859-1
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: nil

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:


Setting the file name via `set-visited-file-name' incorrectly changes
the major mode according to the new file name only. For example,
changing the name of a file containing `// -*- C++ -*-' as its first
line from `test.h' to `test2.h' changes the major mode from c++-mode
to c-mode. An important side effect is that the same thing happens
when writing the file to a different name (`C-x C-w').

This is not consistent and also not what the documentation claims.
>From the info pages (`Choosing Modes'):

      The commands `C-x C-w' and `set-visited-file-name' change to a new
   major mode if the new file name implies a mode (*note Saving::).
   However, this does not happen if the buffer contents specify a major
   mode, and certain "special" major modes do not allow the mode to
   change.  You can turn off this mode-changing feature by setting
   `change-major-mode-with-file-name' to `nil'.

`C-h v change-major-mode-with-file-name <RET>' gives:

   change-major-mode-with-file-name's value is t

   Documentation:
   *Non-nil means C-x C-w should set the major mode from the file name.
   However, the mode will not be changed if
   (1) a local variables list or the `-*-' line specifies a major mode, or
   (2) the current major mode is a "special" mode,
      not suitable for ordinary files, or
   (3) the new file name does not particularly specify any mode.

Not all that important, but annoying...

Regards,
-Frank Schimmel


Recent input:
C-s C-s C-a C-x C-g <next> C-s C-s C-s C-a <next> C-s 
C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s 
C-a C-x k <return> t C-s m o d e <right> <left> <return> 
1 <next> <down> <up> <up> <next> <down> <down> <down> 
<down> <down> <left> <right> C-h c C-x C-w <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <S-right> C-h v <return> C-a C-x o C-SPC 
M-> <right> <up> <up> <up> M-w C-x k <return> C-x 0 
l l l <next> <up> M-x r e p o <tab> r <tab> <retur
n>

Recent messages:
Wrote /tmp/test.h
Wrote /tmp/test2.h
Note: file is write protected
Mark saved where search started [7 times]
C-x C-w runs the command write-file
Type C-x 1 to remove help window.  C-M-v to scroll the help.
Mark set [2 times]
call-interactively: End of buffer
Making completion list...
Loading emacsbug...done