Subject: Re: [PATCH v6] diff.c: keep arrow(=>) on show_stats()'s shortened filename part to make rename visible.

From: Junio C Hamano <[email-masked]>
Date: Thu, 17 Oct 2013 12:29:26 -0700

Yoshioka Tsuneo <[email-masked]> writes:

> "git diff -M --stat" can detect rename and show renamed file name like
> "foofoofoo => barbarbar".
> Before this commit, this output is shortened always by omitting left most
> part like "...foo => barbarbar". So, if the destination filename is too long,
> source filename putting left or arrow can be totally omitted like
> "...barbarbar", without including any of "foofoofoo =>".
> In such a case where arrow symbol is omitted, there is no way to know
> whether the file is renamed or existed in the original.
> Make sure there is always an arrow, like "...foo => ...bar".
> The output can contain curly braces('{','}') for grouping.
> So, in general, the output format is "<pfx>{<mid_a> => <mid_b>}<sfx>"
> To keep arrow("=>"), try to omit <pfx> as long as possible at first
> because later part or changing part will be the more important part.
> If it is not enough, shorten <mid_a>, <mid_b>, and <sfx> trying to
> have the maximum length the same because those will be equally important.

I somehow find this solid wall of text extremely hard to
read. Adding a blank line as a paragraph break may make it easier to
read, perhaps.

Also it is customary in our history to omit the full-stop from the
patch title on the Subject: line.

> +	name_len = pfx->len + a_mid->len + b_mid->len + sfx->len + strlen(arrow)
> +		+ (use_curly_braces ? 2 : 0);
> +
> +	if (name_len <= name_width) {
> +		/* Everthing fits in name_width */
> +		return;
> +	}

Logic up to this point seems good; drop {} around a single statement
"return;", i.e.

	if (name_len <= name_width)
        	return; /* everything fits */

> +		} else {
> +			if (pfx->len > strlen(dots)) {
> +				/*
> +				 * Just omitting left of '{' is not enough
> +				 * name will be "...{SOMETHING}SOMETHING"
> +				 */
> +				strbuf_reset(pfx);
> +				strbuf_addstr(pfx, dots);
> +			}

(mental note) ... otherwise, i.e. with a short common prefix, the
final result will be "ab{SOMETHING}SOMETHING", which is also fine
for the purpose of the remainder of this function.

> +		}
> +	}
> +
> +	/* available length for a_mid, b_mid and sfx */
> +	len = name_width - strlen(arrow) - (use_curly_braces ? 2 : 0);
> +
> +	/* a_mid, b_mid, sfx will be have the same max, including ellipsis("..."). */
> +	part_length[0] = a_mid->len;
> +	part_length[1] = b_mid->len;
> +	part_length[2] = sfx->len;
> +
> +	qsort(part_length, sizeof(part_length)/sizeof(part_length[0]), sizeof(part_length[0])
> +		  , compare_size_t_descending_order);

In our code, comma does not come at the beginning of continued
line.

> +	if (part_length[1] + part_length[1] + part_length[2] <= len) {
> +		/*
> +		 * "{...foofoo => barbar}file"
> +		 * There is only one omitted part.
> +		 */
> +		max_part_len = len - part_length[1] - part_length[2];

It would be clearer to explicitly set remainder to zero here, and
omit the initialization of the variable.  That would make what the
three parts of if/elseif/else do more consistent.

> +	} else if (part_length[2] + part_length[2] + part_length[2] <= len) {
> +		/*
> +		 * "{...foofoo => ...barbar}file"
> +		 * There are 2 omitted parts.
> +		 */
> +		max_part_len = (len - part_length[2]) / 2;
> +		remainder_part_len = (len - part_length[2]) - max_part_len * 2;
> +	} else {
> +		/*
> +		 * "{...ofoo => ...rbar}...file"
> +		 * There are 3 omitted parts.
> +		 */
> +		max_part_len = len / 3;
> +		remainder_part_len = len - (max_part_len) * 3;
> +	}

I am not sure if distributing the burden of truncation equally to
three parts so that the resulting pieces are of similar lengths is
really a good idea.  Between these two

	{...SourceDirectory => ...nationDirectory}...ileThatWasMoved 
	{...ceDirectory => ...ionDirectory}nameOfTheFileThatWasMoved

that attempt to show that the file nameOfTheFileThatWasMoved was
moved from the longSourceDirectory to the DestinationDirectory, the
latter is much more informative, I would think.

> diff --git a/t/t4001-diff-rename.sh b/t/t4001-diff-rename.sh
> index 2f327b7..03d6371 100755
> --- a/t/t4001-diff-rename.sh
> +++ b/t/t4001-diff-rename.sh
> @@ -156,4 +156,16 @@ test_expect_success 'rename pretty print common prefix and suffix overlap' '
>  	test_i18ngrep " d/f/{ => f}/e " output
>  '
>  
> +test_expect_success 'rename of very long path shows =>' '
> +	mkdir long_dirname_that_does_not_fit_in_a_single_line &&
> +	mkdir another_extremely_long_path_but_not_the_same_as_the_first &&
> +	cp path1 long_dirname*/ &&
> +	git add long_dirname*/path1 &&
> +	test_commit add_long_pathname &&
> +	git mv long_dirname*/path1 another_extremely_*/ &&
> +	test_commit move_long_pathname &&
> +	git diff -M --stat HEAD^ HEAD >output &&
> +	test_i18ngrep "=>.*path1" output

Does this have to be i18ngrep?  I had a feeling that we would not
want this part of the output localized, in which case "grep" may be
more appropriate.

> +'
> +
>  test_done