bug#40407: [PATCH] slow ENCODE_FILE and DECODE_FILE

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

Eli Zaretskii <eliz@gnu.org> writes:

>> -  if (BUFFERP (dst_object))
>> +  if (EQ (dst_object, Qt))
>> +    {
>> +      /* Fast path for ASCII-only input and an ASCII-compatible coding:
>> +         act as identity.  */
>> +      Lisp_Object attrs = CODING_ID_ATTRS (coding.id);
>> +      if (! NILP (CODING_ATTR_ASCII_COMPAT (attrs))
>> +          && (STRING_MULTIBYTE (string)
>> +              ? (chars == bytes) : string_ascii_p (string)))
>> +        return string;

While using the latest master branch, I noticed this became the cause of
decoding error.

The simple reproducible test is,

	(decode-coding-string "&abc" 'utf-7-imap)
        => "&abc"

like the above result, decoding utf-7-imap didn't work.

Because (coding-system-get 'utf-7-imap :ascii-compatible-p) => t.

I'm not sure, 'utf-7* should be fixed as non ascii-compatible, or
string_ascii_p() should check more strictly.

[BTW,

(define-coding-system 'utf-7-imap
  "UTF-7 encoding of Unicode, IMAP version (RFC 2060)"
  :coding-type 'utf-8
  :mnemonic ?u
  :charset-list '(unicode)
  :ascii-compatible-p nil		;; <=== added this line
  :pre-write-conversion 'utf-7-imap-pre-write-conversion
  :post-read-conversion 'utf-7-imap-post-read-conversion)

doesn't work. Because define-coding-system-internal overwrites
ascii-compatible-p.]

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>