Merge branch 'ap/maint-diff-rename-avoid-overlap'

The logic used by "git diff -M --stat" to shorten the names of
files before and after a rename did not work correctly when the
common prefix and suffix between the two filenames overlapped.

* ap/maint-diff-rename-avoid-overlap:
  tests: make sure rename pretty print works
  diff: prevent pprint_rename from underrunning input
  diff: Fix rename pretty-print when suffix and prefix overlap

diff.c

@@ -1264,6 +1264,7 @@ static char *pprint_rename(const char *a, const char *b)
 	const char *new = b;
 	struct strbuf name = STRBUF_INIT;
 	int pfx_length, sfx_length;
+	int pfx_adjust_for_slash;
 	int len_a = strlen(a);
 	int len_b = strlen(b);
 	int a_midlen, b_midlen;
@@ -1290,7 +1291,18 @@ static char *pprint_rename(const char *a, const char *b)
 	old = a + len_a;
 	new = b + len_b;
 	sfx_length = 0;
-	while (a <= old && b <= new && *old == *new) {
+	/*
+	 * If there is a common prefix, it must end in a slash.  In
+	 * that case we let this loop run 1 into the prefix to see the
+	 * same slash.
+	 *
+	 * If there is no common prefix, we cannot do this as it would
+	 * underrun the input strings.
+	 */
+	pfx_adjust_for_slash = (pfx_length ? 1 : 0);
+	while (a + pfx_length - pfx_adjust_for_slash <= old &&
+	       b + pfx_length - pfx_adjust_for_slash <= new &&
+	       *old == *new) {
 		if (*old == '/')
 			sfx_length = len_a - (old - a);
 		old--;

t/t4001-diff-rename.sh

@@ -102,4 +102,58 @@ test_expect_success 'setup for many rename source candidates' '
 	grep warning actual.err
 '
 
+test_expect_success 'rename pretty print with nothing in common' '
+	mkdir -p a/b/ &&
+	: >a/b/c &&
+	git add a/b/c &&
+	git commit -m "create a/b/c" &&
+	mkdir -p c/b/ &&
+	git mv a/b/c c/b/a &&
+	git commit -m "a/b/c -> c/b/a" &&
+	git diff -M --summary HEAD^ HEAD >output &&
+	test_i18ngrep " a/b/c => c/b/a " output &&
+	git diff -M --stat HEAD^ HEAD >output &&
+	test_i18ngrep " a/b/c => c/b/a " output
+'
+
+test_expect_success 'rename pretty print with common prefix' '
+	mkdir -p c/d &&
+	git mv c/b/a c/d/e &&
+	git commit -m "c/b/a -> c/d/e" &&
+	git diff -M --summary HEAD^ HEAD >output &&
+	test_i18ngrep " c/{b/a => d/e} " output &&
+	git diff -M --stat HEAD^ HEAD >output &&
+	test_i18ngrep " c/{b/a => d/e} " output
+'
+
+test_expect_success 'rename pretty print with common suffix' '
+	mkdir d &&
+	git mv c/d/e d/e &&
+	git commit -m "c/d/e -> d/e" &&
+	git diff -M --summary HEAD^ HEAD >output &&
+	test_i18ngrep " {c/d => d}/e " output &&
+	git diff -M --stat HEAD^ HEAD >output &&
+	test_i18ngrep " {c/d => d}/e " output
+'
+
+test_expect_success 'rename pretty print with common prefix and suffix' '
+	mkdir d/f &&
+	git mv d/e d/f/e &&
+	git commit -m "d/e -> d/f/e" &&
+	git diff -M --summary HEAD^ HEAD >output &&
+	test_i18ngrep " d/{ => f}/e " output &&
+	git diff -M --stat HEAD^ HEAD >output &&
+	test_i18ngrep " d/{ => f}/e " output
+'
+
+test_expect_success 'rename pretty print common prefix and suffix overlap' '
+	mkdir d/f/f &&
+	git mv d/f/e d/f/f/e &&
+	git commit -m "d/f/e d/f/f/e" &&
+	git diff -M --summary HEAD^ HEAD >output &&
+	test_i18ngrep " d/f/{ => f}/e " output &&
+	git diff -M --stat HEAD^ HEAD >output &&
+	test_i18ngrep " d/f/{ => f}/e " output
+'
+
 test_done