Re: [PATCH v4 1/2] diff.c: When appropriate, use utf8_strwidth(), part1

> When unicode filenames (encoded in UTF-8) are used, the visible width
> on the screen is not the same as strlen(filename).
>
> For example, `git log --stat` may produce an output like this:
>
> [snip the header]
>
>  Arger.txt  | 1 +
>  Ärger.txt | 1 +
>  2 files changed, 2 insertions(+)
>
> A side note: the original report was about cyrillic filenames.
> After some investigations it turned out that
> a) This is not a problem with "ambiguous characters" in unicode
> b) The same problem exists for all unicode code points (so we
>   can use Latin based Umlauts for demonstrations below)
>
> The 'Ä' takes the same space on the screen as the 'A'.
> But needs one more byte in memory, so the the `git log --stat` output
> for "Arger.txt" (!) gets mis-aligned:
> The maximum length is derived from "Ärger.txt", 10 bytes in memory,
> 9 positions on the screen. That is why "Arger.txt" gets one extra ' '
> for aligment, it needs 9 bytes in memory.
> If there was a file "Ö", it would be correctly aligned by chance,
> but "Öhö" would not.
>
> The solution is of course, to use utf8_strwidth() instead of strlen()
> when dealing with the width on screen.
>
> Side note 1:
> Needed changes for this fix are split into 2 commits:
> This commit only changes strlen() into utf8_strwidth() in diff.c:
> The next commit will add tests and further needed changes.

> Side note 2:
> Junio C Hamano suspects that there is probably more work to be done,
> in a separate commit:
> Code in diff.c::pprint_rename() that "abbreviates" overly long pathnames
> and "transforms" renames lines like
> "a/b/c -> a/B/c" into the shorter
> "a/{b->B}/c" form, and IIRC this is all byte based.

>
> Reported-by: Alexander Meshcheryakov <alexander.s.m@gmail.com>
> Signed-off-by: Torsten Bögershausen <tboegi@web.de>
> ---
>  diff.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/diff.c b/diff.c
> index 974626a621..b5df464de5 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -2620,7 +2620,7 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
>  			continue;
>  		}
>  		fill_print_name(file);
> -		len = strlen(file->print_name);
> +		len = utf8_strwidth(file->print_name);
>  		if (max_len < len)
>  			max_len = len;
>
> @@ -2743,7 +2743,7 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
>  		 * "scale" the filename
>  		 */
>  		len = name_width;
> -		name_len = strlen(name);
> +		name_len = utf8_strwidth(name);
>  		if (name_width < name_len) {
>  			char *slash;
>  			prefix = "...";
> --
> 2.34.0