Backport purgeUnusedDependencies

models/migrations/migrations.go

@@ -300,7 +300,10 @@ var migrations = []Migration{
 //      minor revision and when the actual migration is executed again on the next major upgrade).
 //    * The function must not rely on data structures that might not be present in the branch
 //      it is backported to, unless its safe that it will add the column itself.
-var backports = []Migration{}
+var backports = []Migration{
+	// v117 -> v117.1
+	NewMigration("remove dependencies from deleted repositories", purgeUnusedDependencies),
+}
 
 // Migrate database to current version
 func Migrate(x *xorm.Engine) error {

models/migrations/v117.1.go

@@ -0,0 +1,18 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+func purgeUnusedDependencies(x *xorm.Engine) error {
+
+	if _, err := x.Exec("DELETE FROM issue_dependency WHERE issue_id NOT IN (SELECT id FROM issue)"); err != nil {
+		return err
+	}
+	_, err := x.Exec("DELETE FROM issue_dependency WHERE dependency_id NOT IN (SELECT id FROM issue)")
+	return err
+}