rebase: be stricter when reading state files containing oids

The state files for 'onto' and 'orig_head' should contain a full hex
oid, change the reading functions from get_oid() to get_oid_hex() to
reflect this. They should also name commits and not tags so add and use
a function that looks up a commit from an oid like
lookup_commit_reference() but without dereferencing tags.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -429,9 +429,9 @@ static int read_basic_state(struct rebase_options *opts)
 	opts->head_name = starts_with(head_name.buf, "refs/") ?
 		xstrdup(head_name.buf) : NULL;
 	strbuf_release(&head_name);
-	if (get_oid(buf.buf, &oid))
-		return error(_("could not get 'onto': '%s'"), buf.buf);
-	opts->onto = lookup_commit_or_die(&oid, buf.buf);
+	if (get_oid_hex(buf.buf, &oid) ||
+	    !(opts->onto = lookup_commit_object(the_repository, &oid)))
+		return error(_("invalid onto: '%s'"), buf.buf);
 
 	/*
 	 * We always write to orig-head, but interactive rebase used to write to
@@ -446,7 +446,7 @@ static int read_basic_state(struct rebase_options *opts)
 	} else if (!read_oneliner(&buf, state_dir_path("head", opts),
 				  READ_ONELINER_WARN_MISSING))
 		return -1;
-	if (get_oid(buf.buf, &opts->orig_head))
+	if (get_oid_hex(buf.buf, &opts->orig_head))
 		return error(_("invalid orig-head: '%s'"), buf.buf);
 
 	if (file_exists(state_dir_path("quiet", opts)))

commit.c

@@ -59,6 +59,14 @@ struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref
 	return c;
 }
 
+struct commit *lookup_commit_object(struct repository *r,
+				    const struct object_id *oid)
+{
+	struct object *obj = parse_object(r, oid);
+	return obj ? object_as_type(obj, OBJ_COMMIT, 0) : NULL;
+
+}
+
 struct commit *lookup_commit(struct repository *r, const struct object_id *oid)
 {
 	struct object *obj = lookup_object(r, oid);

commit.h

@@ -64,6 +64,19 @@ enum decoration_type {
 void add_name_decoration(enum decoration_type type, const char *name, struct object *obj);
 const struct name_decoration *get_name_decoration(const struct object *obj);
 
+/*
+ * Look up commit named by "oid" respecting replacement objects.
+ * Returns NULL if "oid" is not a commit or does not exist.
+ */
+struct commit *lookup_commit_object(struct repository *r, const struct object_id *oid);
+
+/*
+ * Look up commit named by "oid" without replacement objects or
+ * checking for object existence. Returns the requested commit if it
+ * is found in the object cache, NULL if "oid" is in the object cache
+ * but is not a commit and a newly allocated unparsed commit object if
+ * "oid" is not in the object cache.
+ */
 struct commit *lookup_commit(struct repository *r, const struct object_id *oid);
 struct commit *lookup_commit_reference(struct repository *r,
 				       const struct object_id *oid);