Delete Labels & IssueLabels on Repo Delete too (#15039)

* Doctor: find IssueLabels without existing label

* on Repo Delete: delete labels & issue_labels too

* performance nits

* Add Migration: Delete orphaned IssueLabels

* Migration v174: use Sync2

* USE sess !!!

* better func name

* code format & comment

* RAW SQL

* Update models/migrations/v176.go

* next try?

3 files changed, 58 insertions, 2 deletions

diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index 3427b5dec1..2c85ebdfd7 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -295,11 +295,13 @@ var migrations = []Migration{
 	// v173 -> v174
 	NewMigration("Add time_id column to Comment", addTimeIDCommentColumn),
 	// v174 -> v175
-	NewMigration("create repo transfer table", addRepoTransfer),
+	NewMigration("Create repo transfer table", addRepoTransfer),
 	// v175 -> v176
 	NewMigration("Fix Postgres ID Sequences broken by recreate-table", fixPostgresIDSequences),
 	// v176 -> v177
 	NewMigration("Remove invalid labels from comments", removeInvalidLabels),
+	// v177 -> v178
+	NewMigration("Delete orphaned IssueLabels", deleteOrphanedIssueLabels),
 }
 
 // GetCurrentDBVersion returns the current db version
diff --git a/models/migrations/v174.go b/models/migrations/v174.go
index ce337df2b3..5915d3626b 100644
--- a/models/migrations/v174.go
+++ b/models/migrations/v174.go
@@ -5,6 +5,8 @@
 package migrations
 
 import (
+	"fmt"
+
 	"xorm.io/xorm"
 )
 
@@ -19,5 +21,15 @@ func addRepoTransfer(x *xorm.Engine) error {
 		UpdatedUnix int64 `xorm:"INDEX NOT NULL updated"`
 	}
 
-	return x.Sync(new(RepoTransfer))
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	if err := sess.Sync2(new(RepoTransfer)); err != nil {
+		return fmt.Errorf("Sync2: %v", err)
+	}
+
+	return sess.Commit()
 }
diff --git a/models/migrations/v177.go b/models/migrations/v177.go
new file mode 100644
index 0000000000..2329a8dc48
--- /dev/null
+++ b/models/migrations/v177.go
@@ -0,0 +1,42 @@
+// Copyright 2021 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 (
+	"fmt"
+
+	"xorm.io/xorm"
+)
+
+func deleteOrphanedIssueLabels(x *xorm.Engine) error {
+	type IssueLabel struct {
+		ID      int64 `xorm:"pk autoincr"`
+		IssueID int64 `xorm:"UNIQUE(s)"`
+		LabelID int64 `xorm:"UNIQUE(s)"`
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	if err := sess.Sync2(new(IssueLabel)); err != nil {
+		return fmt.Errorf("Sync2: %v", err)
+	}
+
+	if _, err := sess.Exec(`DELETE FROM issue_label WHERE issue_label.id IN (
+		SELECT ill.id FROM (
+			SELECT il.id
+			FROM issue_label AS il
+				LEFT JOIN label ON il.label_id = label.id
+			WHERE
+				label.id IS NULL
+		) AS ill)`); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}