coverity: avoid dereferencing NULL

builtin/bisect.c

@@ -663,6 +663,11 @@ static int bisect_successful(struct bisect_terms *terms)
 
 	refs_read_ref(get_main_ref_store(the_repository), bad_ref, &oid);
 	commit = lookup_commit_reference_by_name(bad_ref);
+	if (!commit) {
+		error(_("could not find commit for '%s'"), bad_ref);
+		free(bad_ref);
+		return BISECT_FAILED;
+	}
 	repo_format_commit_message(the_repository, commit, "%s", &commit_name,
 				   &pp);
 
@@ -806,9 +811,11 @@ static enum bisect_error bisect_start(struct bisect_terms *terms, int argc,
 	 */
 	head = refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
 				       "HEAD", 0, &head_oid, &flags);
-	if (!head)
+	if (!head) {
 		if (repo_get_oid(the_repository, "HEAD", &head_oid))
 			return error(_("bad HEAD - I need a HEAD"));
+		head = "HEAD";
+	}
 
 	/*
 	 * Check if we are bisecting

builtin/diff.c

@@ -579,9 +579,13 @@ int cmd_diff(int argc,
 		obj = deref_tag(the_repository, obj, NULL, 0);
 		if (!obj)
 			die(_("invalid object '%s' given."), name);
-		if (obj->type == OBJ_COMMIT)
-			obj = &repo_get_commit_tree(the_repository,
-						    ((struct commit *)obj))->object;
+		if (obj->type == OBJ_COMMIT) {
+			struct tree *tree = repo_get_commit_tree(
+				the_repository, (struct commit *)obj);
+			if (!tree)
+				die(_("unable to read tree object for commit '%s'"), name);
+			obj = &tree->object;
+		}
 
 		if (obj->type == OBJ_TREE) {
 			if (sdiff.skip && bitmap_get(sdiff.skip, i))

builtin/mailsplit.c

@@ -225,14 +225,14 @@ static int split_mbox(const char *file, const char *dir, int allow_bare,
 	FILE *f = !strcmp(file, "-") ? stdin : fopen(file, "r");
 	int file_done = 0;
 
-	if (isatty(fileno(f)))
-		warning(_("reading patches from stdin/tty..."));
-
 	if (!f) {
 		error_errno("cannot open mbox %s", file);
 		goto out;
 	}
 
+	if (isatty(fileno(f)))
+		warning(_("reading patches from stdin/tty..."));
+
 	do {
 		peek = fgetc(f);
 		if (peek == EOF) {

diffcore-break.c

@@ -289,6 +289,8 @@ void diffcore_merge_broken(void)
 			 */
 			for (j = i + 1; j < q->nr; j++) {
 				struct diff_filepair *pp = q->queue[j];
+				if (!pp)
+					continue;
 				if (pp->broken_pair &&
 				    !strcmp(pp->one->path, pp->two->path) &&
 				    !strcmp(p->one->path, pp->two->path)) {

pack-bitmap.c

@@ -523,6 +523,10 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 
 	if (midx->base_midx) {
 		bitmap_git->base = prepare_midx_bitmap_git(midx->base_midx);
+		if (!bitmap_git->base) {
+			warning(_("could not open bitmap for base MIDX"));
+			goto cleanup;
+		}
 		bitmap_git->base_nr = bitmap_git->base->base_nr + 1;
 	} else {
 		bitmap_git->base_nr = 0;

reftable/stack.c

@@ -171,7 +171,8 @@ void reftable_stack_destroy(struct reftable_stack *st)
 		st->merged = NULL;
 	}
 
-	err = read_lines(st->list_file, &names);
+	if (st->list_file)
+		err = read_lines(st->list_file, &names);
 	if (err < 0) {
 		REFTABLE_FREE_AND_NULL(names);
 	}

remote.c

@@ -2681,6 +2681,8 @@ static int remote_tracking(struct remote *remote, const char *refname,
 {
 	char *dst;
 
+	if (!remote)
+		BUG("remote_tracking() called with NULL remote");
 	dst = apply_refspecs(&remote->fetch, refname);
 	if (!dst)
 		return -1; /* no tracking ref for refname at remote */

replay.c

@@ -36,12 +36,16 @@ static struct commit *peel_committish(struct repository *repo,
 {
 	struct object *obj;
 	struct object_id oid;
+	struct commit *commit;
 
 	if (repo_get_oid(repo, name, &oid))
 		die(_("'%s' is not a valid commit-ish for %s"), name, mode);
 	obj = parse_object_or_die(repo, &oid, name);
-	return (struct commit *)repo_peel_to_type(repo, name, 0, obj,
-						  OBJ_COMMIT);
+	commit = (struct commit *)repo_peel_to_type(repo, name, 0, obj,
+						    OBJ_COMMIT);
+	if (!commit)
+		die(_("'%s' does not point to a commit for %s"), name, mode);
+	return commit;
 }
 
 static char *get_author(const char *message)

revision.c

@@ -1903,8 +1903,13 @@ static int add_parents_only(struct rev_info *revs, const char *arg_, int flags,
 		return 0;
 	while (1) {
 		it = get_reference(revs, arg, &oid, 0);
-		if (!it && revs->ignore_missing)
-			return 0;
+		if (!it) {
+			if (revs->ignore_missing)
+				return 0;
+			if (revs->do_not_die_on_missing_objects)
+				return 0;
+			return -1;
+		}
 		if (it->type != OBJ_TAG)
 			break;
 		if (!((struct tag*)it)->tagged)

shallow.c

@@ -359,7 +359,9 @@ struct write_shallow_data {
 static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 {
 	struct write_shallow_data *data = cb_data;
-	const char *hex = oid_to_hex(&graft->oid);
+	char hex[GIT_MAX_HEXSZ + 1];
+
+	oid_to_hex_r(hex, &graft->oid);
 	if (graft->nr_parent != -1)
 		return 0;
 	if (data->flags & QUICK) {
@@ -370,8 +372,7 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 		struct commit *c = lookup_commit(the_repository, &graft->oid);
 		if (!c || !(c->object.flags & SEEN)) {
 			if (data->flags & VERBOSE)
-				printf("Removing %s from .git/shallow\n",
-				       oid_to_hex(&c->object.oid));
+				printf("Removing %s from .git/shallow\n", hex);
 			return 0;
 		}
 	}

t/t0410-partial-clone.sh

@@ -489,6 +489,24 @@ test_expect_success 'rev-list dies for missing objects on cmd line' '
 	done
 '
 
+test_expect_success '--exclude-promisor-objects with ^@ on missing object' '
+	rm -rf repo &&
+	test_create_repo repo &&
+	test_commit -C repo foo &&
+	test_commit -C repo bar &&
+
+	COMMIT=$(git -C repo rev-parse foo) &&
+	promise_and_delete "$COMMIT" &&
+
+	git -C repo config core.repositoryformatversion 1 &&
+	git -C repo config extensions.partialclone "arbitrary string" &&
+
+	# Ensure that "$COMMIT^@" is handled gracefully even though the
+	# actual commits are missing.
+	git -C repo rev-list --exclude-promisor-objects "$COMMIT^@" >out &&
+	test_must_be_empty out
+'
+
 test_expect_success 'single promisor remote can be re-initialized gracefully' '
 	# ensure one promisor is in the promisors list
 	rm -rf repo &&