On Wed, Jan 14, 2026 at 02:50:02PM -0800, Junio C Hamano wrote:

LorenzoPegorari [off-list ref] writes:

quoted

The `show_stats()` function tries to scale the filenames in the diffstat to
ensure they don't exceed the given `name-width`. It does so by calculating
the "display width" of the characters to be dropped, but then advances the
filename pointer by that number of bytes.

However, the "display width" of a character is not always equal to its byte
count. The result is that sometimes, when displaying UTF-8 characters,
filenames exceed the given `name-width`, and frequently the bytes of the
UTF-8 characters are truncated.

The following is an example of the issue, where the 2 files are "HelloHi" and
"Hello你好", and `name-width=6`:

    ...oHi | 0
    ...<BD><A0>好 | 0

Make the filename pointer move by the actual number of bytes of the
characters to drop from the filename, rather than their display width, using
the `utf8_width()` function.

Signed-off-by: LorenzoPegorari <redacted>
---
 diff.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

Two comments and a half.

 * The change needed for this is surprisingly simple.

It is indeed surprisingly simple, I agree!

 * You already know about samples that may exhibit the issue you are
   addressing.  Can we add it as a test case somewhere in t/
   directory?

Yeah, we should add a test case. I will do it in the next reroll.

 * The NEEDSWORK item addressed by this patch is one of the two
   NEEDSWORK items added by ce8529b2 (diff: leave NEEDWORK notes in
   show_stats() function, 2022-10-21).  Makes me wonder how involved
   the changes would need to be to solve the other one?

Mmh, I see. I'll take a closer look, but at a first glance it doesn't
seem too involved.

Thanks.

Thank you!

quoted

diff --git a/diff.c b/diff.c
index a68ddd2168..271ace5728 100644
--- a/diff.c
+++ b/diff.c

@@ -2859,17 +2859,10 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
 			char *slash;
 			prefix = "...";
 			len -= 3;
-			/*
-			 * NEEDSWORK: (name_len - len) counts the display
-			 * width, which would be shorter than the byte
-			 * length of the corresponding substring.
-			 * Advancing "name" by that number of bytes does
-			 * *NOT* skip over that many columns, so it is
-			 * very likely that chomping the pathname at the
-			 * slash we will find starting from "name" will
-			 * leave the resulting string still too long.
-			 */
-			name += name_len - len;
+
+			while (name_len > len)
+				name_len -= utf8_width((const char**)&name, NULL);
+
 			slash = strchr(name, '/');
 			if (slash)
 				name = slash;