name-hash: properly fold directory names in adjust_dirname_case()

Correct the pointer arithmetic in adjust_dirname_case() so that it calls
find_dir_entry() with the correct string length.  Previously passing in
"dir1/foo" would pass a length of 6 instead of the correct 4.  This resulted in
find_dir_entry() never finding the entry and so the subsequent memcpy that would
fold the name to the version with the correct case never executed.

Add a test to validate the corrected behavior with name folding of directories.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

name-hash.c

@@ -201,12 +201,12 @@ void adjust_dirname_case(struct index_state *istate, char *name)
 		if (*ptr == '/') {
 			struct dir_entry *dir;
 
-			ptr++;
-			dir = find_dir_entry(istate, name, ptr - name + 1);
+			dir = find_dir_entry(istate, name, ptr - name);
 			if (dir) {
 				memcpy((void *)startPtr, dir->name + (startPtr - name), ptr - startPtr);
-				startPtr = ptr;
+				startPtr = ptr + 1;
 			}
+			ptr++;
 		}
 	}
 }

t/t0050-filesystem.sh

@@ -80,7 +80,21 @@ test_expect_success 'merge (case change)' '
 	git merge topic
 '
 
-
+test_expect_success CASE_INSENSITIVE_FS 'add directory (with different case)' '
+	git reset --hard initial &&
+	mkdir -p dir1/dir2 &&
+	echo >dir1/dir2/a &&
+	echo >dir1/dir2/b &&
+	git add dir1/dir2/a &&
+	git add dir1/DIR2/b &&
+	git ls-files >actual &&
+	cat >expected <<-\EOF &&
+		camelcase
+		dir1/dir2/a
+		dir1/dir2/b
+	EOF
+	test_cmp expected actual
+'
 
 test_expect_failure CASE_INSENSITIVE_FS 'add (with different case)' '
 	git reset --hard initial &&