Re: Silly "git gc" UI issue.

[Junio C Hamano <gitster@pobox.com>]

A few commands that parse --expire=<time> command line option
behaves silly when given nonsense input.  For example

    $ git prune --no-expire
    Segmentation falut
    $ git prune --expire=npw; echo $?
    129

Both come from parse_opt_expiry_date_cb().

The former is because the function is not prepared to see arg==NULL
(for "--no-expire", it is a norm; "--expire" at the end of the
command line could be made to pass NULL, if it is told that the
argument is optional, but we don't so we do not have to worry about
that case).

The latter is because it does not check the value returned from  the
underlying parse_expiry_date().  

This seems to be a recent regression introduced while we attempted
to avoid spewing the entire usage message when given a correct
option but with an invalid value at 3bb0923f ("parse-options: do not
show usage upon invalid option value", 2018-03-22).

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * I do not expect this to be the final version (not just it lacks
   tests, but I haven't even run existing tests with the change
   yet), but I think I diagnosed the root cause correctly, at least.

 parse-options-cb.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/parse-options-cb.c b/parse-options-cb.c
index c6679cb2cd..872627eafe 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -38,7 +38,11 @@ int parse_opt_approxidate_cb(const struct option *opt, const char *arg,
 int parse_opt_expiry_date_cb(const struct option *opt, const char *arg,
 			     int unset)
 {
-	return parse_expiry_date(arg, (timestamp_t *)opt->value);
+	if (unset)
+		arg = "never";
+	if (parse_expiry_date(arg, (timestamp_t *)opt->value))
+		die("malformed expiration date '%s'", arg);
+	return 0;
 }
 
 int parse_opt_color_flag_cb(const struct option *opt, const char *arg,