last-modified: support sparse checkouts

In a sparse checkout, a user might want to run `last-modified` on a
directory outside the worktree.

And even in non-sparse checkouts, a user might need to run that command
on a directory that does not exist in the worktree.

These use cases should be supported via the `--` separator between
revision and file arguments, which is even advertised in the
documentation. This patch fixes a tiny bug that prevents that from
working.

This fixes git-for-windows#5978

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

builtin/last-modified.c

@@ -525,7 +525,8 @@ int cmd_last_modified(int argc, const char **argv, const char *prefix,
 
 	argc = parse_options(argc, argv, prefix, last_modified_options,
 			     last_modified_usage,
-			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN_OPT);
+			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN_OPT |
+			     PARSE_OPT_KEEP_DASHDASH);
 
 	repo_config(repo, git_default_config, NULL);
 

t/t8020-last-modified.sh

@@ -227,4 +227,12 @@ test_expect_success 'last-modified complains about unknown arguments' '
 	grep "unknown last-modified argument: --foo" err
 '
 
+test_expect_success 'last-modified in sparse checkout' '
+	test_when_finished "git sparse-checkout disable" &&
+	git sparse-checkout set b &&
+	check_last_modified -- a <<-\EOF
+	3 a
+	EOF
+'
+
 test_done