Re: isolating history with buffer-local variables

[Pascal J. Bourguignon]

Nick Helm <nick@tenpoint.co.nz> writes:

> Hello, I'm trying to teach myself some elisp, but I'm having a problem
> with some code that works with buffer-local variables. It seems to
> work as intended for some variables, but not others.
>
> My objective is to create a minor mode that makes Emacs less likely to
> leak private data. 
>
> The approach I've taken is to locally turn off backups and auto-saves,
> and create buffer-local variables to isolate command histories and
> rings that may accumulate private information. My intent is for
> editing to work normally in the private buffer, with local histories
> and the local kill-ring etc all available, but without exposing them
> globally to other buffers and packages like savehist, which should
> continue uninterrupted. When the minor mode is turned off, the local
> variables are killed, reinstating the global bindings.
>
> Here's the code:
>
> (define-minor-mode private-mode
>    "This mode prevents Emacs from creating backups, auto-saves and
>    certain history records for the current buffer. It is useful
>    when editing private data, such as password files, key-chains and
>    secure notes."
>    :init-value nil
>    :lighter " Private"
>    :keymap nil
>    (if (symbol-value private-mode) (progn
>       (setq private-variables '( ;; data to isolate
>          minibuffer-history         ;; <-- not working
>          command-history            ;; ok
>          extended-command-history   ;; <-- not working
>          string-rectangle-history   ;; <-- not working
>          query-replace-history      ;; ok
>          search-ring                ;; ok
>          regexp-search-ring         ;; ok
>          kill-ring                  ;; ok
>          backup-inhibited           ;; ok
>          auto-save-timeout))        ;; ok 
>       (dolist (variable private-variables) (make-local-variable variable)) ;; 
> make local vars
>       (setq backup-inhibited t) ;; locally disable backups
>       (setq auto-save-timeout 0)) ;; locally idle auto-saves
>       ;; TODO: Add idle timer to purge changes to local vars
>     (dolist (variable private-variables) (kill-local-variable variable)))) ;; 
> pop local vars
>
> All the local auto-save/backup vars, local ring vars, and local
> query-replace-history and command-history vars work as intended. But
> minibuffer-history, extended-command-history and
> string-rectangle-history do not. The buffer-local vars for these are
> made as expected, but they are ignored and histories continue to
> accumulate in the global variables.
>
> Any idea why? Anyone have suggestions for a different approach or a
> way around the problem? 
>
> (There is a somewhat relevant discussion here:
> http://lists.gnu.org/archive/html/help-gnu-emacs/2011-10/msg00292.html)

minibuffer-history is used in the minibuffer.  This is a different
buffer.  Therefore it's a different buffer local variable.

I guess a similar problem might be the case for the other variables.


-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
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