Subject: Re: [PATCH 2/4] strbuf: refactor strbuf_trim_trailing_ch()

From: Junio C Hamano <[email-masked]>
Date: Wed, 31 Jul 2024 10:29:00 -0700

Christian Couder <[email-masked]> writes:

> We often have to split strings at some specified terminator character.
> The strbuf_split*() functions, that we can use for this purpose,
> return substrings that include the terminator character, so we often
> need to remove that character.
>
> When it is a whitespace, newline or directory separator, the
> terminator character can easily be removed using an existing triming
> function like strbuf_rtrim(), strbuf_trim_trailing_newline() or
> strbuf_trim_trailing_dir_sep(). There is no function to remove that
> character when it's not one of those characters though.

OK.

> Let's introduce a new strbuf_trim_trailing_ch() function that can be
> used to remove any trailing character, and let's refactor existing code
> that manually removed trailing characters using this new function.

It is disappointing that this new one is not adequate to rewrite any
of the existing strbuf_trim* functions in terms of it, but that's
probably OK.  At least this one we have two existing callers, but
makes me wonder if these callers are doing sensible things in the
first place.  After trimming trailing commas, there may be trailing
newlines to be trimmed, and then again whitespaces around the whole
thing may need to be trimmed---what kind of input is that?  The
value has to be " junk \n\n,,,", but " junk, \n\n, " will only
become "junk, \n\n," without further cleaned up, and it is very
dubious how that is useful.

But that is not an issue this patch introduces ;-)

> diff --git a/trace2/tr2_cfg.c b/trace2/tr2_cfg.c
> index d96d908bb9..356fcd38f4 100644
> --- a/trace2/tr2_cfg.c
> +++ b/trace2/tr2_cfg.c
> @@ -33,10 +33,7 @@ static int tr2_cfg_load_patterns(void)
>  
>  	tr2_cfg_patterns = strbuf_split_buf(envvar, strlen(envvar), ',', -1);
>  	for (s = tr2_cfg_patterns; *s; s++) {
> -		struct strbuf *buf = *s;
> -
> -		if (buf->len && buf->buf[buf->len - 1] == ',')
> -			strbuf_setlen(buf, buf->len - 1);
> +		strbuf_trim_trailing_ch(*s, ',');
>  		strbuf_trim_trailing_newline(*s);
>  		strbuf_trim(*s);
>  	}
> @@ -72,10 +69,7 @@ static int tr2_load_env_vars(void)
>  
>  	tr2_cfg_env_vars = strbuf_split_buf(varlist, strlen(varlist), ',', -1);
>  	for (s = tr2_cfg_env_vars; *s; s++) {
> -		struct strbuf *buf = *s;
> -
> -		if (buf->len && buf->buf[buf->len - 1] == ',')
> -			strbuf_setlen(buf, buf->len - 1);
> +		strbuf_trim_trailing_ch(*s, ',');
>  		strbuf_trim_trailing_newline(*s);
>  		strbuf_trim(*s);
>  	}