Re: sanitized mm-string-to-multibyte

[Katsumi Yamaoka <yamaoka@jpl.org>]

>>>>> Dave Love wrote:
> I found some IMAP messages were crashing Emacs, and I was led to
> mm-string-to-multibyte.  I'm not sure exactly what the crash was due to,
> but the function isn't very sane in Emacs 21.  This version doesn't cons
> a string for each character.  Various uses of the function are at least
> dubious, and I'll send patches later.  mm-with-preserved-unibyte is
> useful for those changes and elsewhere.

> 2009-02-08  Dave Love  <fx@gnu.org>

> 	* mm-util.el (mm-identity-nat, mm-with-preserved-unibyte): New.
> 	(mm-string-to-multibyte): Use them.

Your version of `mm-string-to-multibyte' doesn't seem to convert
a unibyte string to a multibyte string.  In Emacs 21.1~21.4 I got:

(let* ((s1 (string-as-unibyte "a"))
       (s2 (mm-with-preserved-unibyte (string-make-multibyte s1))))
  (list (multibyte-string-p s1) (multibyte-string-p s2)))
 => (nil nil)

(let* ((s1 (string-as-multibyte "a"))
       (s2 (mm-with-preserved-unibyte (string-make-multibyte s1))))
  (list (multibyte-string-p s1) (multibyte-string-p s2)))
 => (t t)

Did I miss something?

> Index: mm-util.el
> ===================================================================
> RCS file: /usr/local/cvsroot/gnus/lisp/mm-util.el,v
> retrieving revision 7.91
> diff -u -r7.91 mm-util.el
> --- mm-util.el	14 Jan 2009 00:52:01 -0000	7.91
> +++ mm-util.el	8 Feb 2009 17:27:12 -0000
> @@ -202,6 +202,22 @@
>      (defalias 'mm-decode-coding-region 'decode-coding-region)
>      (defalias 'mm-encode-coding-region 'encode-coding-region)))

> +(defconst mm-identity-nat (let (l)
> +			    (dotimes (i 256)
> +			      (push (cons i i) l))
> +			    (make-translation-table l))
> +  "Translation table that applies the identity trasnlation.")
> +
> +(defmacro mm-with-preserved-unibyte (&rest body)
> +  "Execute BODY forms while preserving unibyte characters.
> +Such characters are not converted automatically to multibyte ones
> +when, for instance, inserted into a multibyte buffer within the
> +BODY forms."
> +  `(let ((nonascii-translation-table mm-identity-nat))
> +     ,@body))
> +(put 'mm-with-preserved-unibyte 'lisp-indent-function 0)
> +(put 'mm-with-preserved-unibyte 'edebug-form-spec '(body))
> +
>  ;; `string-to-multibyte' is available only in Emacs 22.1 or greater.
>  (defalias 'mm-string-to-multibyte
>    (cond
> @@ -210,11 +226,8 @@
>     ((fboundp 'string-to-multibyte)
>      'string-to-multibyte)
>     (t
> -    (lambda (string)
> -      "Return a multibyte string with the same individual chars as STRING."
> -      (mapconcat
> -       (lambda (ch) (mm-string-as-multibyte (char-to-string ch)))
> -       string "")))))
> +    (lambda (s)
> +      (mm-with-preserved-unibyte (string-make-multibyte s))))))

>  ;; `char-or-char-int-p' is an XEmacs function, not available in Emacs.
>  (eval-and-compile