branch: -d protects upstream branches

index a613148fc7..87f0aa4051 100644
@@ -203,6 +203,58 @@ enum delete_branch_flags {
 	DELETE_BRANCH_DRY_RUN = (1 << 4),
 };
 
+struct stacked_branch_data {
+	struct strset *deletable_branch_names;
+	struct strset *protected_branch_names;
+};
+
+static int collect_stacked_branch_base(const struct reference *ref,
+				       void *cb_data)
+{
+	struct stacked_branch_data *data = cb_data;
+	const char *branch_name;
+	struct branch *branch;
+	const char *upstream_refname;
+	const char *upstream_branch_name;
+
+	if (!skip_prefix(ref->name, "refs/heads/", &branch_name))
+		BUG("expected local branch ref, got '%s'", ref->name);
+	if (strset_contains(data->deletable_branch_names, branch_name))
+		return 0;
+
+	branch = branch_get(branch_name);
+	upstream_refname = branch_get_upstream(branch, NULL);
+	if (!upstream_refname ||
+	    !skip_prefix(upstream_refname, "refs/heads/",
+			 &upstream_branch_name) ||
+	    !strset_contains(data->deletable_branch_names,
+			    upstream_branch_name))
+		return 0;
+
+	strset_add(data->protected_branch_names, upstream_branch_name);
+	return 0;
+}
+
+static void protect_stacked_branch_bases(struct ref_store *refs,
+					 struct strset *deletable_branch_names,
+					 struct strset *protected_branch_names)
+{
+	struct stacked_branch_data data = {
+		.deletable_branch_names = deletable_branch_names,
+		.protected_branch_names = protected_branch_names,
+	};
+	struct refs_for_each_ref_options opts = {
+		.prefix = "refs/heads/",
+	};
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	refs_for_each_ref_ext(refs, collect_stacked_branch_base, &data, &opts);
+
+	strset_for_each_entry(protected_branch_names, &iter, entry)
+		strset_remove(deletable_branch_names, entry->key);
+}
+
 static int check_branch_commit(const char *branchname, const char *refname,
 			       const struct object_id *oid, struct commit *head_rev,
 			       int kinds, unsigned int flags)

@@ -718,58 +770,6 @@ static int parse_opt_forked(const struct option *opt, const char *arg, int unset
 	return 0;
 }
 
-struct stacked_branch_data {
-	struct strset *deletable_branch_names;
-	struct strset *protected_branch_names;
-};
-
-static int collect_stacked_branch_base(const struct reference *ref,
-				       void *cb_data)
-{
-	struct stacked_branch_data *data = cb_data;
-	const char *branch_name;
-	struct branch *branch;
-	const char *upstream_refname;
-	const char *upstream_branch_name;
-
-	if (!skip_prefix(ref->name, "refs/heads/", &branch_name))
-		BUG("expected local branch ref, got '%s'", ref->name);
-	if (strset_contains(data->deletable_branch_names, branch_name))
-		return 0;
-
-	branch = branch_get(branch_name);
-	upstream_refname = branch_get_upstream(branch, NULL);
-	if (!upstream_refname ||
-	    !skip_prefix(upstream_refname, "refs/heads/",
-			 &upstream_branch_name) ||
-	    !strset_contains(data->deletable_branch_names,
-			    upstream_branch_name))
-		return 0;
-
-	strset_add(data->protected_branch_names, upstream_branch_name);
-	return 0;
-}
-
-static void protect_stacked_branch_bases(struct ref_store *refs,
-					 struct strset *deletable_branch_names,
-					 struct strset *protected_branch_names)
-{
-	struct stacked_branch_data data = {
-		.deletable_branch_names = deletable_branch_names,
-		.protected_branch_names = protected_branch_names,
-	};
-	struct refs_for_each_ref_options opts = {
-		.prefix = "refs/heads/",
-	};
-	struct hashmap_iter iter;
-	struct strmap_entry *entry;
-
-	refs_for_each_ref_ext(refs, collect_stacked_branch_base, &data, &opts);
-
-	strset_for_each_entry(protected_branch_names, &iter, entry)
-		strset_remove(deletable_branch_names, entry->key);
-}
-
 static void clear_deleted_upstreams(struct strset *protected_branch_names,
 				    struct strset *deletable_branch_names)
 {

index 87f0aa4051..7f76789027 100644
@@ -294,12 +294,13 @@ static int delete_branches(int argc, const char **argv, int kinds,
 	struct object_id oid;
 	char *name = NULL;
 	const char *fmt;
-	int i;
 	int ret = 0;
 	int remote_branch = 0;
 	struct strbuf bname = STRBUF_INIT;
 	enum interpret_branch_kind allowed_interpret;
 	struct string_list refs_to_delete = STRING_LIST_INIT_DUP;
+	struct strset deletable_branch_names = STRSET_INIT;
+	struct strset protected_branch_names = STRSET_INIT;
 	struct string_list_item *item;
 	int branch_name_pos;
 	const char *fmt_remotes = "refs/remotes/%s";

@@ -326,7 +327,7 @@ static int delete_branches(int argc, const char **argv, int kinds,
 	    !(flags & DELETE_BRANCH_NO_HEAD_FALLBACK))
 		head_rev = lookup_commit_reference(the_repository, &head_oid);
 
-	for (i = 0; i < argc; i++, strbuf_reset(&bname)) {
+	for (int i = 0; i < argc; i++, strbuf_reset(&bname)) {
 		char *target = NULL;
 		int ref_flags = 0;
 

@@ -397,11 +398,42 @@ static int delete_branches(int argc, const char **argv, int kinds,
 		item->util = xstrdup((ref_flags & REF_ISBROKEN) ? "broken"
 				    : (ref_flags & REF_ISSYMREF) ? target
 				    : repo_find_unique_abbrev(the_repository, &oid, DEFAULT_ABBREV));
+		if (!remote_branch && !(flags & (DELETE_BRANCH_FORCE |
+						 DELETE_BRANCH_SKIP_UNMERGED)))
+			strset_add(&deletable_branch_names, bname.buf);
 
 	next:
 		free(target);
 	}
 
+	if (!remote_branch &&
+	    !(flags & (DELETE_BRANCH_FORCE | DELETE_BRANCH_SKIP_UNMERGED)) &&
+	    refs_to_delete.nr) {
+		protect_stacked_branch_bases(get_main_ref_store(the_repository),
+					     &deletable_branch_names, &protected_branch_names);
+		for (size_t i = refs_to_delete.nr; i; i--) {
+			const char *branch_name;
+
+			item = &refs_to_delete.items[i - 1];
+			if (!skip_prefix(item->string, "refs/heads/",
+					 &branch_name))
+				BUG("expected local branch ref, got '%s'",
+				    item->string);
+			if (strset_contains(&deletable_branch_names, branch_name))
+				continue;
+
+			error(_("the branch '%s' is an upstream of another branch"),
+			      branch_name);
+			advise_if_enabled(ADVICE_FORCE_DELETE_BRANCH,
+					  _("If you are sure you want to delete it, "
+					    "run 'git branch -D %s'"),
+					  branch_name);
+			ret = 1;
+			unsorted_string_list_delete_item(&refs_to_delete, i - 1,
+							 1);
+		}
+	}
+
 	if (!(flags & DELETE_BRANCH_DRY_RUN) &&
 	    refs_delete_refs(get_main_ref_store(the_repository), NULL, &refs_to_delete, REF_NO_DEREF))
 		ret = 1;

@@ -428,6 +460,8 @@ static int delete_branches(int argc, const char **argv, int kinds,
 		free(describe_ref);
 	}
 	string_list_clear(&refs_to_delete, 0);
+	strset_clear(&deletable_branch_names);
+	strset_clear(&protected_branch_names);
 
 	free(name);
 	strbuf_release(&bname);