bug#65071: 29.1; RMAIL changed on disk leads to rmail-error-bad-format

[Eli Zaretskii]

> From: emacs-bug@rulnick.com
> Cc: 65071@debbugs.gnu.org
> Date: Sat, 05 Aug 2023 06:31:10 -0400
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: <emacs-bug@rulnick.com>
> >> Date: Fri, 04 Aug 2023 14:18:52 -0400
> >> 
> >> In Emacs 29.1, starting with no ~/RMAIL file and empty primary mail
> >> spool file ('$' indicates command line terminal prompt outside Emacs):
> >> 
> >>   $ mail me@foo ... # send a message to myself
> >> 
> >>   emacs -Q
> >> 
> >>   M-x RMAIL # retrieves/reads message
> >> 
> >>   $ cat /dev/null > ~/RMAIL # clear (or otherwise modify) RMAIL file
> >> 
> >>   $ mail me@foo ... # send another message to myself
> >> 
> >>   M-x RMAIL
> >> 
> >>   "File RMAIL changed on disk. Reread from disk? (yes or no) " yes
> >> 
> >>     "rmail-error-bad-format: Message is not a valid RFC 822 (or later)
> >>     message" and:
> >> 
> >>       mode changes from RMAIL to fundamental
> >> 
> >>       ~/RMAIL file on disk looks good (proper RFC 822 file)
> >> 
> >>       ~/RMAIL file as visited in buffer looks bad, can be seen (e.g.,
> >>         upon immediate save) to be missing top "From " and other header
> >>         lines ("Return-Path:", "Received:", etc.)
> >
> > Does using "M-x revert-buffer RET" avoid the problem?
> >
> > In any case, this is not how you are supposed to read new email into
> > an existing Rmail buffer.  You are supposed to use the 'g' command.
> 
> 1. M-x revert-buffer RET does not avoid or solve the problem completely;
>    the contents from disk appear to be restored as expected but the
>    buffer remains in Fundamental mode. However, following this with
>    RMAIL-mode RET does appear to at least be a fix.
> 
> 2. Yes, I should have said 'g' rather than 'M-x rmail RET' in the second
>    instance. The bug report applies in this case as well.

Then I'm sorry, I don't understand the recipe, because I cannot
reproduce this on my system.  After

   $ cat /dev/null > ~/RMAIL

the ~/RMAIL file is empty, right?  And the Emacs session that used
that file was terminated, i.e. Emacs doesn't run when you clear the
~/RMAIL file?

Then you do "M-x RMAIL"?   But it should be "M-x rmail", lower-case,
right?  Or is the command something else, like

  C-u M-x rmail RET ~/RMAIL RET

?

And how do you modify the recipe to use the 'g' command? can you show
the recipe with 'g' instead of a new "M-x rmail".