[bug-libunistring] Re: case-mapping part of a Unicode string

[Paolo Bonzini]

>   size_t uppercased_part_3_4_len;
>   uint8_t *uppercased_part_3_4 =
>     u8_ct_toupper (pointer3, pointer4 - pointer3,
>                    u8_casing_prefix_context (s, pointer3 - s),
>                    u8_casing_suffix_context (pointer4, s_end - pointer4),
>                    iso639_language, NULL, NULL, &uppercased_part_3_4_len);
>   size_t uppercased_part_6_8_len;
>   uint8_t *uppercased_part_6_8 =
>     u8_ct_toupper (pointer6, pointer8 - pointer6,
>                    u8_casing_prefix_context (s, pointer6 - s),
>                    u8_casing_suffix_context (pointer8, s_end - pointer6),
>                    iso639_language, NULL, NULL, &uppercased_part_6_8_len);

Regarding this part, how could I use the incremental context 
computation?  I can imagine how to use u8_casing_prefixes_context, but 
not the same for suffixes:

  forgot_the_type_name pre = u8_casing_prefix_context (s, pointer3 - s);
  forgot_the_type_name suf = u8_casing_suffix_context (pointer4,
                                                       s_end - pointer4);
  size_t uppercased_part_3_4_len;
  uint8_t *uppercased_part_3_4 =
    u8_ct_toupper (pointer3, pointer4 - pointer3, pre, suf,
                   iso639_language, NULL, NULL,
                   &uppercased_part_3_4_len);

  pre = u8_casing_prefixes_context (pointer4, pointer6 - pointer4, pre);
  suf = u8_casing_suffix_context (pointer8, s_end - pointer8, suf);
  size_t uppercased_part_6_8_len;
  uint8_t *uppercased_part_6_8 =
    u8_ct_toupper (pointer6, pointer8 - pointer6, pre, suf,
                   iso639_language, NULL, NULL,
                   &uppercased_part_6_8_len);

Is this intentional?  Does u8_casing_suffixes_context make sense only 
when scanning backwards?

If so, you should add something like: "u8_casing_prefixes_context is 
convenient if you are scanning a string forwards, while 
u8_casing_suffixes_context does the same function when scanning 
backwards.  For the suffix context on forward scans you should just pass 
the entire remaining part of the string u8_casing_suffix_context, and 
likewise for the prefix context on backward scans."

(Note that in my case I have no control on the characters I ask you to 
case-fold; it may be that I ask you to case-fold a combining accent and 
only that).

> And finally use u8_normalize to normalize the result to NFC
> (optional, but recommended):

It would be nice to have something in coreutils doing normalization...

Paolo