[PATCH 0/2] [GSoC][RFC/Patch] FIX: use utf8_strnwidth for line_prefix in diff.c

[PATCH 0/2] [GSoC][RFC/Patch] FIX: use utf8_strnwidth for line_prefix in diff.c

[Md Isfarul Haque via GitGitGadget]

This patch adresses diff.c:2721 and proposes the fix using a new function.

Md Isfarul Haque (2):
  FIX: use utf8_strnwidth for line_prefix in diff.c
  FIX memory leak in one branch

 diff.c | 19 +++++++++++++++++--
 diff.h |  1 +
 2 files changed, 18 insertions(+), 2 deletions(-)


base-commit: e02ecfcc534e2021aae29077a958dd11c3897e4c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1653%2FInnocentZero%2Fdiff_needswork-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1653/InnocentZero/diff_needswork-v1
Pull-Request: https://github.com/git/git/pull/1653
-- 
gitgitgadget

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

[Md Isfarul Haque via GitGitGadget]

From: Md Isfarul Haque <isfarul.876@gmail.com>

This patch adresses diff.c:2721 and proposes the fix using a new function.

Signed-off-by: Md Isfarul Haque <isfarul.876@gmail.com>
---
 diff.c | 18 ++++++++++++++++--
 diff.h |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/diff.c b/diff.c
index a89a6a6128a..e3223b8ce5b 100644
--- a/diff.c
+++ b/diff.c
@@ -2300,6 +2300,20 @@ const char *diff_line_prefix(struct diff_options *opt)
 	return msgbuf->buf;
 }
 
+const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)
+{
+	struct strbuf *msgbuf = (struct strbuf *)malloc(sizeof(*msgbuf));
+	if (!opt->output_prefix){
+		msgbuf->buf = "";
+		msgbuf->len = 0;
+		msgbuf->alloc = 1;
+	}
+	else {
+		msgbuf = opt->output_prefix(opt, opt->output_prefix_data);
+	}
+	return msgbuf;
+}
+
 static unsigned long sane_truncate_line(char *line, unsigned long len)
 {
 	const char *cp;
@@ -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);
 	else
 		width = options->stat_width ? options->stat_width : 80;
 	number_width = decimal_width(max_change) > number_width ?
diff --git a/diff.h b/diff.h
index 66bd8aeb293..6eb8dc9a97e 100644
--- a/diff.h
+++ b/diff.h
@@ -460,6 +460,7 @@ const char *diff_get_color(int diff_use_color, enum color_diff ix);
 
 const char *diff_line_prefix(struct diff_options *);
 
+const struct strbuf *diff_line_prefix_buf(struct diff_options *);
 
 extern const char mime_boundary_leader[];
 
-- 
gitgitgadget

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

[Christian Couder]

On Wed, Jan 24, 2024 at 3:04 PM Md Isfarul Haque via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Md Isfarul Haque <isfarul.876@gmail.com>
>
> This patch adresses diff.c:2721 and proposes the fix using a new function.

Please give more details here about what is currently at diff.c:2721
and what the patch is fixing, as lines at diff.c:2721 could move to a
different location if some changes are made to diff.c before your
patches get merged or after they get merged.

Also if the patch is addressing an issue in a code comment I would
expect the corresponding code comment to be removed by the patch.

About the subject, maybe "diff: use utf8_strnwidth() for line_prefix"
is already better.

> Signed-off-by: Md Isfarul Haque <isfarul.876@gmail.com>
> ---
>  diff.c | 18 ++++++++++++++++--
>  diff.h |  1 +
>  2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/diff.c b/diff.c
> index a89a6a6128a..e3223b8ce5b 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -2300,6 +2300,20 @@ const char *diff_line_prefix(struct diff_options *opt)
>         return msgbuf->buf;
>  }
>
> +const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)

This function seems to be used only in diff.c, so it could be static.

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

[Md Isfarul Haque]

On 1/25/24 01:31, Christian Couder wrote:
> On Wed, Jan 24, 2024 at 3:04 PM Md Isfarul Haque via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
>>
>> From: Md Isfarul Haque <isfarul.876@gmail.com>
>>
>> This patch adresses diff.c:2721 and proposes the fix using a new function.
> 
> Please give more details here about what is currently at diff.c:2721
> and what the patch is fixing, as lines at diff.c:2721 could move to a
> different location if some changes are made to diff.c before your
> patches get merged or after they get merged.
> 
> Also if the patch is addressing an issue in a code comment I would
> expect the corresponding code comment to be removed by the patch.

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

> About the subject, maybe "diff: use utf8_strnwidth() for line_prefix"
> is already better.
> 
>> Signed-off-by: Md Isfarul Haque <isfarul.876@gmail.com>
>> ---
>>  diff.c | 18 ++++++++++++++++--
>>  diff.h |  1 +
>>  2 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/diff.c b/diff.c
>> index a89a6a6128a..e3223b8ce5b 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -2300,6 +2300,20 @@ const char *diff_line_prefix(struct diff_options *opt)
>>         return msgbuf->buf;
>>  }
>>
>> +const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)
> 
> This function seems to be used only in diff.c, so it could be static.

As Junio pointed out, I will probably use the existing function with slight
modifications and use it. Besides, having unnecessary allocations and frees
will probably only add overhead.

-- 

Thanks and regards
Md. Isfarul Haque

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

[Junio C Hamano]

"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).

> +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.

> @@ -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?

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.

Thanks.

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

[Md Isfarul Haque]

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

[PATCH 2/2] FIX memory leak in one branch

[Md Isfarul Haque via GitGitGadget]

From: Md Isfarul Haque <isfarul.876@gmail.com>

Signed-off-by: Md Isfarul Haque <isfarul.876@gmail.com>
---
 diff.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/diff.c b/diff.c
index e3223b8ce5b..9fa00103a6b 100644
--- a/diff.c
+++ b/diff.c
@@ -2309,6 +2309,7 @@ const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)
 		msgbuf->alloc = 1;
 	}
 	else {
+		free(msgbuf);
 		msgbuf = opt->output_prefix(opt, opt->output_prefix_data);
 	}
 	return msgbuf;
-- 
gitgitgadget

Re: [PATCH 2/2] FIX memory leak in one branch

[Junio C Hamano]

"Md Isfarul Haque via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Md Isfarul Haque <isfarul.876@gmail.com>
>
> Signed-off-by: Md Isfarul Haque <isfarul.876@gmail.com>
> ---
>  diff.c | 1 +
>  1 file changed, 1 insertion(+)

We do not need to see that you are just as human as other developers
and are prone to make mistakes that you need to fix it in a
follow-up.  In other words, please do not introduce a bug in [1/2]
only to be fixed in [2/2].  By squashing these two patches into one,
you can pretend as if you are a perfect developer and never leaked
memory ;-).

> diff --git a/diff.c b/diff.c
> index e3223b8ce5b..9fa00103a6b 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -2309,6 +2309,7 @@ const struct strbuf *diff_line_prefix_buf(struct diff_options *opt)
>  		msgbuf->alloc = 1;
>  	}
>  	else {
> +		free(msgbuf);
>  		msgbuf = opt->output_prefix(opt, opt->output_prefix_data);
>  	}
>  	return msgbuf;

But as I said, I do not see a need for this helper function in the
first place, so...

Re: [PATCH 0/2] [GSoC][RFC/Patch] FIX: use utf8_strnwidth for line_prefix in diff.c

[Junio C Hamano]

"Md Isfarul Haque via GitGitGadget" <gitgitgadget@gmail.com> writes:

> This patch adresses diff.c:2721 and proposes the fix using a new function.

Yay.  My favorite long-time pet-peeve topic.

>
> Md Isfarul Haque (2):
>   FIX: use utf8_strnwidth for line_prefix in diff.c
>   FIX memory leak in one branch

Our convention does not use "FIX" and other prefix on the subject.
Please check Documentation/SubmittingPatches.

Thanks.