Merge branch 'lp/diff-stat-utf8-display-width-fix' into jch

The computation of column width made by "git diff --stat" was
confused when pathnames contain non-ASCII characters.

* lp/diff-stat-utf8-display-width-fix:
  t4073: add test for diffstat paths length when containing UTF-8 chars
  diff: improve scaling of filenames in diffstat to handle UTF-8 chars

diff.c

@@ -2859,17 +2859,12 @@ 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;
+			if (len < 0)
+				len = 0;
+
+			while (name_len > len)
+				name_len -= utf8_width((const char**)&name, NULL);
+
 			slash = strchr(name, '/');
 			if (slash)
 				name = slash;

t/meson.build

@@ -498,6 +498,7 @@ integration_tests = [
   't4070-diff-pairs.sh',
   't4071-diff-minimal.sh',
   't4072-diff-max-depth.sh',
+  't4073-diff-stat-name-width.sh',
   't4100-apply-stat.sh',
   't4101-apply-nonl.sh',
   't4102-apply-rename.sh',

t/t4073-diff-stat-name-width.sh

@@ -0,0 +1,61 @@
+#!/bin/sh
+
+test_description='git-diff check diffstat filepaths length when containing UTF-8 chars'
+
+. ./test-lib.sh
+
+
+create_files () {
+	mkdir -p "d你好" &&
+	touch "d你好/f再见"
+}
+
+test_expect_success 'setup' '
+	git init &&
+	git config core.quotepath off &&
+	git commit -m "Initial commit" --allow-empty &&
+	create_files &&
+	git add . &&
+	git commit -m "Added files"
+'
+
+test_expect_success 'test name-width long enough for filepath' '
+	git diff HEAD~1 HEAD --stat --stat-name-width=12 >out &&
+	grep "d你好/f再见 |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=11 >out &&
+	grep "d你好/f再见 |" out
+'
+
+test_expect_success 'test name-width not long enough for dir name' '
+	git diff HEAD~1 HEAD --stat --stat-name-width=10 >out &&
+	grep ".../f再见  |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=9 >out &&
+	grep ".../f再见 |" out
+'
+
+test_expect_success 'test name-width not long enough for slash' '
+	git diff HEAD~1 HEAD --stat --stat-name-width=8 >out &&
+	grep "...f再见 |" out
+'
+
+test_expect_success 'test name-width not long enough for file name' '
+	git diff HEAD~1 HEAD --stat --stat-name-width=7 >out &&
+	grep "...再见 |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=6 >out &&
+	grep "...见  |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=5 >out &&
+	grep "...见 |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=4 >out &&
+	grep "...  |" out
+'
+
+test_expect_success 'test name-width minimum length' '
+	git diff HEAD~1 HEAD --stat --stat-name-width=3 >out &&
+	grep "... |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=2 >out &&
+	grep "... |" out &&
+	git diff HEAD~1 HEAD --stat --stat-name-width=1 >out &&
+	grep "... |" out
+'
+
+test_done