bug#5937: 23.1.95; why saving empty abbrev tables

[Stefan Monnier]

> Why empty abbrev tables are saved to file?

Don't know.

> It seems to make it more difficult for editing (edit-abbrevs) because
> the buffer is full of empty abbrev.  I wonder if saving only non-empty
> tables is better and user friendlier.

It does sound like a good idea.  Any objection?

> (defun abbrev-table-empty-p (table)
>   "Return nil if there are no abbrev symbols in abbrev table object TABLE."
>   (unless (abbrev-table-p table)
>     (error "Non abbrev table object"))
>   (not (catch 'some
>          (mapatoms (lambda (sym)
>                      (when (abbrev-symbol (symbol-name sym) table)
>                        (throw 'some t)))
>                    table))))
> (defadvice write-abbrev-file (around nonempty-abbrev-tables activate)
>   "Ignore empty abbrev tables when writing to FILE."
>   (let ((file (ad-get-arg 0))
>         (coding-system-for-write 'emacs-mule)
>         (tables (loop for table in abbrev-table-name-list
>                       unless (abbrev-table-empty-p (symbol-value table))
>                       collect table)))
>     (or (and file (> (length file) 0)) (setq file abbrev-file-name))
>     (with-temp-file file
>       (insert ";;-*-coding: emacs-mule;-*-\n")
>       (dolist (table (sort tables
>                            (lambda (s1 s2)
>                              (string< (symbol-name s1)
>                                       (symbol-name s2)))))
>         (insert-abbrev-table-description table nil)))))

Obviously, defadvice wouldn't be the right approach for us.
And rather than (abbrev-symbol (symbol-name sym) table), we can use
(symbol-value sym).
We should also eliminate abbrev tables that only contain "system
abbrevs".


        Stefan