alternates: use fspathcmp to detect duplicates

On a case-insensitive filesystem, we should realize that
"a/objects" and "A/objects" are the same path. We already
use fspathcmp() to check against the main object directory,
but until recently we couldn't use it for comparing against
other alternates (because their paths were not
NUL-terminated strings). But now we can, so let's do so.

Note that we also need to adjust count-objects to load the
config, so that it can see the setting of core.ignorecase
(this is required by the test, but is also a general bugfix
for users of count-objects).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/count-objects.c

@@ -97,6 +97,8 @@ int cmd_count_objects(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	git_config(git_default_config, NULL);
+
 	argc = parse_options(argc, argv, prefix, opts, count_objects_usage, 0);
 	/* we do not take arguments other than flags for now */
 	if (argc)

sha1_file.c

@@ -260,7 +260,7 @@ static int alt_odb_usable(struct strbuf *path, const char *normalized_objdir)
 	 * thing twice, or object directory itself.
 	 */
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		if (!strcmp(path->buf, alt->path))
+		if (!fspathcmp(path->buf, alt->path))
 			return 0;
 	}
 	if (!fspathcmp(path->buf, normalized_objdir))

t/t5613-info-alternate.sh

@@ -119,4 +119,21 @@ test_expect_success 'relative duplicates are eliminated' '
 	test_cmp expect actual.alternates
 '
 
+test_expect_success CASE_INSENSITIVE_FS 'dup finding can be case-insensitive' '
+	git init --bare insensitive.git &&
+	# the previous entry for "A" will have used uppercase
+	cat >insensitive.git/objects/info/alternates <<-\EOF &&
+	../../C/.git/objects
+	../../a/.git/objects
+	EOF
+	cat >expect <<-EOF &&
+	alternate: $(pwd)/C/.git/objects
+	alternate: $(pwd)/B/.git/objects
+	alternate: $(pwd)/A/.git/objects
+	EOF
+	git -C insensitive.git count-objects -v >actual &&
+	grep ^alternate: actual >actual.alternates &&
+	test_cmp expect actual.alternates
+'
+
 test_done