this-command oddness

[David Byers]

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In GNU Emacs 21.2.1 (sparc-sun-solaris2.8, X toolkit)
 of 2002-03-18 on sen14.ida.liu.se
configured using `configure  --prefix=/pkg/emacs-21.2 --with-xpm --with-jpeg 
--with-tiff --with-gif --with-png --with-x'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: en_US.ISO8859-1
  value of $LC_CTYPE: iso_8859_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
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

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


In the following command:

    (defun db--test-this-command (file)
       (interactive)
       (completing-read "Hit RET: " nil)
       (message "%S" this-command))

I expected the message "db--test-this-command" in the echo area.
Instead I get "exit-minibuffer". Furthermore, last-command becomes
bound to exit-minibuffer rather than db--test-this-command. 

Similarly, in the following command:

    (defun db--test-this-command (file)
       (interactive "f")
       (message "%S" this-command))

I expected the message "db--test-this-command" in the echo area.
Instead I get "minibuffer-complete-and-exit" (after entering a file
name).

The value of this-command in a post-command-hook that is run after one
of the examples above will be "minibuffer-complete-and-exit or
"exit-minibuffer" or rather than "db--test-this-command". Similarly,
the value of last-command is affected.

I assume that this is the result of completing-read interactively
reading characters from the user, re-binding this-command in the
process.

In my opinion, neither completing-read, nor read-from-minibuffer
should alter this-command. I *definitely* think that interactive
should not alter this-command, regardless of what it calls in turn (if
this-command is altered in the call to interactive, the command never
gets a chance to examine the original value of this-command).


I propose that one of the following changes be made:

* Alter completing-read and read-from-minibuffer so they save the
  value of this-command on entry and restore it on exit or at least
  alter interactive so it saves the value of this-command on entry and
  restores it on exit.

* Update the documentation of this-command and last-command to reflect
  the face that they may not behave as expected. Examples like those I
  have shown would be appropriate in the elisp manual. Update the
  documentation for post-command-hook to indicate that this-command
  may have been inadvertently altered by the command that ran last.

I would have submitted patches, but don't have the time to write them
at the moment. Sorry.

-- 
David Byers.