Re: [PATCH v2 1/1] diff.c: When appropriate, use utf8_strwidth()

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Torsten,

On Mon, 29 Aug 2022, Torsten Bögershausen wrote:

> On Mon, Aug 29, 2022 at 02:04:42PM +0200, Johannes Schindelin wrote:
> > >
> > > The choosen solution is to split code in diff.c like this
> > >
> > > strbuf_addf(&out, "%-*s", len, name);
> > >
> > > into something like this:
> > >
> > > size_t num_padding_spaces = 0;
> > > // [snip]
> > > if (len > utf8_strwidth(name))
> > >     num_padding_spaces = len - utf8_strwidth(name);
> > > strbuf_addf(&out, "%s", name);
> > > if (num_padding_spaces)
> > >     strbuf_addchars(&out, ' ', num_padding_spaces);
> >
> > ... this sounds like it would benefit from beinv refactored into a
> > separate function, e.g. `strbuf_add_padded(buf, utf8string)`, both for
> > readability as well as for self-documentation.
>
> Yes, but:
> All (tm) strbuf() functions use an unsigned size_t, and are not
> tolerant against passing 0 as "do nothing".

I am missing something, as this seems not to contradict the idea of
`strbuf_add_padded()`. Simply provide the desired width as a `size_t`,
compare the width of the actual added string, and if it is shorter, pad
with spaces. At no stage does this require a signed type, all involved
values are strictly non-negative.

> >
> > Also, it is unclear to me why we have to evaluate `utf8_strwidth()`
> > _twice_ and why we do not assign the result to a variable called `width`
> > and then have a conditional like
> >
> > 	if (width < len) /* pad to `len` columns */
> > 		strbuf_addchars(&out, ' ' , len - width);
> >
> > instead. That would sound more logical to me.
>
> This is caused by the logic in diff.c:
>   /*
>    * Find the longest filename and max number of changes
>    */
>    for (i = 0; (i < count) && (i < data->nr); i++) {
>        struct diffstat_file *file = data->files[i];
>        [snip]
>        len = utf8_strwidth(file->print_name);
>        if (max_width < len)
>           max_width = len;
> // and later
>     /*
>      * From here name_width is the width of the name area,
>      * and graph_width is the width of the graph area.
>      * max_change is used to scale graph properly.
>      */
>     for (i = 0; i < count; i++) {
>     /*
>      * "scale" the filename
>      */
>      // TB: Which means either shortening it with ...
>      // Or padding it, if needed, and here we need
>      // another
>      name_len = utf8_strwidth(name);

I was referring to this part of the commit message:

	if (len > utf8_strwidth(name))
		num_padding_spaces = len - utf8_strwidth(name);

Here, we evaluate `utf8_strwidth(name)`, compare it to `len`, and if the
former was smaller, we evaluate the same function call _again_.

What my feedback intended to suggest was to store the result and reuse it:

	name_width = utf8_strwidth(name);
	if (name_width < len)
		num_padding_spaces = len - name_width;

Ciao,
Dscho