Subject: Re: [PATCH v3] diff.c: keep arrow(=>) on show_stats()'s shortened filename part to make rename visible.

From: Thomas Rast <[email-masked]>
Date: Sun, 13 Oct 2013 22:29:29 +0200

Hi,

Yoshioka Tsuneo <[email-masked]> writes:

> "git diff -M --stat" can detect rename and show renamed file name like
> "foofoofoo => barbarbar", but if destination filename is long the line
> is shortened like "...barbarbar" so there is no way to know whether the
> file is renamed or existed in the source commit.

Thanks for your patch!  I think this is indeed something that should be
fixed.

Can you explain the algorithm chosen in the commit message or a block
comment in the code?  I find it much easier to follow large code blocks
(like the one you added) with a prior notion of what it tries to do.

  [As an aside, Documentation/SubmittingPatches says

    The body should provide a meaningful commit message, which:

      . explains the problem the change tries to solve, iow, what is wrong
        with the current code without the change.

      . justifies the way the change solves the problem, iow, why the
        result with the change is better.

      . alternate solutions considered but discarded, if any.

  Observe that you explained the first item very well, but not the
  others.]

> This commit makes it visible like "...foo => ...bar".

Also, you should rewrite this to be in the imperative mood:

  Make sure there is always an arrow, e.g., "...foo => ...bar".

or some such.

  [Again from SubmittingPatches:

    Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
    instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
    to do frotz", as if you are giving orders to the codebase to change
    its behaviour.]

> Signed-off-by: Tsuneo Yoshioka <[email-masked]>
> ---
>  diff.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 51 insertions(+), 7 deletions(-)

Can you add a test?  Perhaps like the one below.  (You can squash it
into your commit if you like it.)

Note that in the test, the generated line looks like this:

 {..._does_not_fit_in_a_single_line => .../path1                          | 0

I don't want to go all bikesheddey, but I think it's somewhat
unfortunate that the elided parts do not correspond to each other.  In
particular, I think the closing brace should not be omitted.  Perhaps
something like this would be ideal (making it up on the spot, don't
count characters):

 {...a_single_line => ..._as_the_first}/path1                          | 0

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
+'
+
 test_done

-- 
Thomas Rast
[email-masked]