push --force-with-lease: tie it all together

This teaches the deepest part of the callchain for "git push" (and
"git send-pack") to enforce "the old value of the ref must be this,
otherwise fail this push" (aka "compare-and-swap" / "--lockref").

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

builtin/send-pack.c

@@ -55,6 +55,11 @@ static void print_helper_status(struct ref *ref)
 			msg = "needs force";
 			break;
 
+		case REF_STATUS_REJECT_STALE:
+			res = "error";
+			msg = "stale info";
+			break;
+
 		case REF_STATUS_REJECT_ALREADY_EXISTS:
 			res = "error";
 			msg = "already exists";

remote.c

@@ -1396,12 +1396,13 @@ int match_push_refs(struct ref *src, struct ref **dst,
 }
 
 void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
-	int force_update)
+			     int force_update)
 {
 	struct ref *ref;
 
 	for (ref = remote_refs; ref; ref = ref->next) {
 		int force_ref_update = ref->force || force_update;
+		int reject_reason = 0;
 
 		if (ref->peer_ref)
 			hashcpy(ref->new_sha1, ref->peer_ref->new_sha1);
@@ -1416,6 +1417,26 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 		}
 
 		/*
+		 * Bypass the usual "must fast-forward" check but
+		 * replace it with a weaker "the old value must be
+		 * this value we observed".  If the remote ref has
+		 * moved and is now different from what we expect,
+		 * reject any push.
+		 *
+		 * It also is an error if the user told us to check
+		 * with the remote-tracking branch to find the value
+		 * to expect, but we did not have such a tracking
+		 * branch.
+		 */
+		if (ref->expect_old_sha1) {
+			if (ref->expect_old_no_trackback ||
+			    hashcmp(ref->old_sha1, ref->old_sha1_expect))
+				reject_reason = REF_STATUS_REJECT_STALE;
+		}
+
+		/*
+		 * The usual "must fast-forward" rules.
+		 *
 		 * Decide whether an individual refspec A:B can be
 		 * pushed.  The push will succeed if any of the
 		 * following are true:
@@ -1433,24 +1454,26 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 		 *     passing the --force argument
 		 */
 
-		if (!ref->deletion && !is_null_sha1(ref->old_sha1)) {
-			int why = 0; /* why would this push require --force? */
-
+		else if (!ref->deletion && !is_null_sha1(ref->old_sha1)) {
 			if (!prefixcmp(ref->name, "refs/tags/"))
-				why = REF_STATUS_REJECT_ALREADY_EXISTS;
+				reject_reason = REF_STATUS_REJECT_ALREADY_EXISTS;
 			else if (!has_sha1_file(ref->old_sha1))
-				why = REF_STATUS_REJECT_FETCH_FIRST;
+				reject_reason = REF_STATUS_REJECT_FETCH_FIRST;
 			else if (!lookup_commit_reference_gently(ref->old_sha1, 1) ||
 				 !lookup_commit_reference_gently(ref->new_sha1, 1))
-				why = REF_STATUS_REJECT_NEEDS_FORCE;
+				reject_reason = REF_STATUS_REJECT_NEEDS_FORCE;
 			else if (!ref_newer(ref->new_sha1, ref->old_sha1))
-				why = REF_STATUS_REJECT_NONFASTFORWARD;
-
-			if (!force_ref_update)
-				ref->status = why;
-			else if (why)
-				ref->forced_update = 1;
+				reject_reason = REF_STATUS_REJECT_NONFASTFORWARD;
 		}
+
+		/*
+		 * "--force" will defeat any rejection implemented
+		 * by the rules above.
+		 */
+		if (!force_ref_update)
+			ref->status = reject_reason;
+		else if (reject_reason)
+			ref->forced_update = 1;
 	}
 }
 

remote.h

@@ -107,6 +107,7 @@ struct ref {
 		REF_STATUS_REJECT_NODELETE,
 		REF_STATUS_REJECT_FETCH_FIRST,
 		REF_STATUS_REJECT_NEEDS_FORCE,
+		REF_STATUS_REJECT_STALE,
 		REF_STATUS_UPTODATE,
 		REF_STATUS_REMOTE_REJECT,
 		REF_STATUS_EXPECTING_REPORT

send-pack.c

@@ -227,6 +227,7 @@ int send_pack(struct send_pack_args *args,
 		case REF_STATUS_REJECT_ALREADY_EXISTS:
 		case REF_STATUS_REJECT_FETCH_FIRST:
 		case REF_STATUS_REJECT_NEEDS_FORCE:
+		case REF_STATUS_REJECT_STALE:
 		case REF_STATUS_UPTODATE:
 			continue;
 		default:

transport-helper.c

@@ -683,6 +683,11 @@ static int push_update_ref_status(struct strbuf *buf,
 			free(msg);
 			msg = NULL;
 		}
+		else if (!strcmp(msg, "stale info")) {
+			status = REF_STATUS_REJECT_STALE;
+			free(msg);
+			msg = NULL;
+		}
 	}
 
 	if (*ref)
@@ -756,6 +761,7 @@ static int push_refs_with_push(struct transport *transport,
 		/* Check for statuses set by set_ref_status_for_push() */
 		switch (ref->status) {
 		case REF_STATUS_REJECT_NONFASTFORWARD:
+		case REF_STATUS_REJECT_STALE:
 		case REF_STATUS_REJECT_ALREADY_EXISTS:
 		case REF_STATUS_UPTODATE:
 			continue;

transport.c

@@ -709,6 +709,10 @@ static int print_one_push_status(struct ref *ref, const char *dest, int count, i
 		print_ref_status('!', "[rejected]", ref, ref->peer_ref,
 						 "needs force", porcelain);
 		break;
+	case REF_STATUS_REJECT_STALE:
+		print_ref_status('!', "[rejected]", ref, ref->peer_ref,
+						 "stale info", porcelain);
+		break;
 	case REF_STATUS_REMOTE_REJECT:
 		print_ref_status('!', "[remote rejected]", ref,
 						 ref->deletion ? NULL : ref->peer_ref,
@@ -1078,6 +1082,7 @@ static int run_pre_push_hook(struct transport *transport,
 	for (r = remote_refs; r; r = r->next) {
 		if (!r->peer_ref) continue;
 		if (r->status == REF_STATUS_REJECT_NONFASTFORWARD) continue;
+		if (r->status == REF_STATUS_REJECT_STALE) continue;
 		if (r->status == REF_STATUS_UPTODATE) continue;
 
 		strbuf_reset(&buf);