push --force-with-lease: implement logic to populate old_sha1_expect[]

This plugs the push_cas_option data collected by the command line
option parser to the transport system with a new function
apply_push_cas(), which is called after match_push_refs() has
already been called.

At this point, we know which remote we are talking to, and what
remote refs we are going to update, so we can fill in the details
that may have been missing from the command line, such as

 (1) what abbreviated refname the user gave us matches the actual
     refname at the remote; and

 (2) which remote-tracking branch in our local repository to read
     the value of the object to expect at the remote.

to populate the old_sha1_expect[] field of each of the remote ref.
As stated in the documentation, the use of remote-tracking branch
as the default is a tentative one, and we may come up with a better
logic as we gain experience.

Still nobody uses this information, which is the topic of the next
patch.

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

1 files changed, 61 insertions, 0 deletions

diff --git a/remote.c b/remote.c
index 0d383533d4..52e3a12d6c 100644
--- a/remote.c
+++ b/remote.c
@@ -1978,3 +1978,64 @@ int parseopt_push_cas_option(const struct option *opt, const char *arg, int unse
 {
 	return parse_push_cas_option(opt->value, arg, unset);
 }
+
+int is_empty_cas(const struct push_cas_option *cas)
+{
+	return !cas->use_tracking_for_rest && !cas->nr;
+}
+
+/*
+ * Look at remote.fetch refspec and see if we have a remote
+ * tracking branch for the refname there.  Fill its current
+ * value in sha1[].
+ * If we cannot do so, return negative to signal an error.
+ */
+static int remote_tracking(struct remote *remote, const char *refname,
+			   unsigned char sha1[20])
+{
+	char *dst;
+
+	dst = apply_refspecs(remote->fetch, remote->fetch_refspec_nr, refname);
+	if (!dst)
+		return -1; /* no tracking ref for refname at remote */
+	if (read_ref(dst, sha1))
+		return -1; /* we know what the tracking ref is but we cannot read it */
+	return 0;
+}
+
+static void apply_cas(struct push_cas_option *cas,
+		      struct remote *remote,
+		      struct ref *ref)
+{
+	int i;
+
+	/* Find an explicit --<option>=<name>[:<value>] entry */
+	for (i = 0; i < cas->nr; i++) {
+		struct push_cas *entry = &cas->entry[i];
+		if (!refname_match(entry->refname, ref->name, ref_rev_parse_rules))
+			continue;
+		ref->expect_old_sha1 = 1;
+		if (!entry->use_tracking)
+			hashcpy(ref->old_sha1_expect, cas->entry[i].expect);
+		else if (remote_tracking(remote, ref->name, ref->old_sha1_expect))
+			ref->expect_old_no_trackback = 1;
+		return;
+	}
+
+	/* Are we using "--<option>" to cover all? */
+	if (!cas->use_tracking_for_rest)
+		return;
+
+	ref->expect_old_sha1 = 1;
+	if (remote_tracking(remote, ref->name, ref->old_sha1_expect))
+		ref->expect_old_no_trackback = 1;
+}
+
+void apply_push_cas(struct push_cas_option *cas,
+		    struct remote *remote,
+		    struct ref *remote_refs)
+{
+	struct ref *ref;
+	for (ref = remote_refs; ref; ref = ref->next)
+		apply_cas(cas, remote, ref);
+}