Re: [PATCH 1/2] FIX: use utf8_strnwidth for line_prefix in diff.c

[Md Isfarul Haque <isfarul.876@gmail.com>]

On 1/25/24 01:38, Junio C Hamano wrote:
> "Md Isfarul Haque via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Md Isfarul Haque <isfarul.876@gmail.com>
>>
>> This patch adresses diff.c:2721 and proposes the fix using a new function.
> 
> Once the issue has fully been addressed, it is expected that the
> NEEDSWORK comment there would be removed, making this proposed log
> message useless.  Make it a habit to write a log message that is
> self-contained enough to help readers (including yourself in the
> future when you have forgotten the details of what you did in this
> commit).
> 

I understand. Sorry for the mess-up. I will keep it in mind the next time.

>> +const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)
>> +{
> 
> Given that there is only one caller of this function in the same
> file, I do not see a reason why this needs to be extern and exported
> in diff.h (actually I do not see a need for this helper at all).
> 
> When dealing with a string buffer, it is much more common in this
> codebase for the caller to prepare a strbuf (often on its stack) and
> pass a pointer to it to helper functions.  I.e.
> 
> 	static void prepare_diff_line_prefix_buf(struct strbuf *buf,
> 						struct diff_options *opt)
> 	{
> 		... stuff whatever you need into the string buffer ...
>                 strbuf_add(buf, ...);
> 	}
> 
> 	/* in show_stats() */
> 	struct strbuf line_prefix = STRBUF_INIT;
> 	...
> 	prepare_diff_line_prefix_buf(&line_prefix, options);
> 	... use line_prefix and ...
> 	... release the resource before returning ...
> 	strbuf_release(&line_prefix);
> 	
> is more common and less prone to resource leak over time.
> 

Ah, this is indeed very neat. Didn't strike me. I'm not extremely familiar
with the codebase and was unaware of this practice. I will follow this 
pattern in the future.

>> @@ -2635,7 +2649,7 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
>>  	int width, name_width, graph_width, number_width = 0, bin_width = 0;
>>  	const char *reset, *add_c, *del_c;
>>  	int extra_shown = 0;
>> -	const char *line_prefix = diff_line_prefix(options);
>> +	const struct strbuf *line_prefix = diff_line_prefix_buf(options);
>>  	struct strbuf out = STRBUF_INIT;
>>  
>>  	if (data->nr == 0)
>> @@ -2718,7 +2732,7 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
>>  	 * used to correctly count the display width instead of strlen().
>>  	 */
>>  	if (options->stat_width == -1)
>> -		width = term_columns() - strlen(line_prefix);
>> +		width = term_columns() - utf8_strnwidth(line_prefix->buf, line_prefix->len, 1);
> 
> I do not see the need for any of the diff_line_prefix_buf() related
> changes, only to do this change.  You have a const char *line_prefix
> at this point, and utf8_strnwidth() wants to know its length, so
> what you need is to massage the parameter to match what it wants.
> Perhaps even something simple and dumb like
> 
> 	utf8_strnwidth(line_prefix, strlen(line_prefix), 1);
> 
> might be sufficient to replace strlen(line_prefix) in the original?

It was more of a force of habit on my end, since I usually do not use
functions that do not have a limit on the length they are reading.
However, considering that the string is generated by another function
and is most likely safe as it was used earlier, I will implement 
this suggestion.

> 
> This patch hopefully will change the behaviour of the command.  A
> patch needs to also protect the change from future breakages by
> adding a test or two to demonstrate the desired behaviour.  Such a
> test should pass with the code change in the patch, and should fail
> when the code change in the patch gets reverted.
> 

Alright. Where should I add the test? A new/existing test in t/t4013 
or t4124-log-graph-octopus.sh?

-- 

Thanks and regards,
Md Isfarul Haque