[DB] Forgejo database migrations

- Implements https://codeberg.org/forgejo/discussions/issues/32#issuecomment-918737
- Allows to add Forgejo-specific migrations that don't interfere with Gitea's migration logic. Please do note that we cannot liberally add migrations for Gitea tables, as they might do their own migrations in a future version on that table, and that could undo our migrations. Luckily,  we don't have a scenario where that's needed and thus not taken into account.

Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/795
(cherry picked from commit 8ee32978c0)
(cherry picked from commit c240b34f59)
(cherry picked from commit 03936c6492)
(cherry picked from commit a20ed852f8)
(cherry picked from commit 1dfa82676f)
(cherry picked from commit c39ae0bf8a)

models/forgejo_migrations/migrate.go

@@ -0,0 +1,139 @@
+// Copyright 2023 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package forgejo_migrations //nolint:revive
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"xorm.io/xorm"
+	"xorm.io/xorm/names"
+)
+
+// ForgejoVersion describes the Forgejo version table. Should have only one row with id = 1.
+type ForgejoVersion struct {
+	ID      int64 `xorm:"pk autoincr"`
+	Version int64
+}
+
+type Migration struct {
+	description string
+	migrate     func(*xorm.Engine) error
+}
+
+// NewMigration creates a new migration.
+func NewMigration(desc string, fn func(*xorm.Engine) error) *Migration {
+	return &Migration{desc, fn}
+}
+
+// This is a sequence of additional Forgejo migrations.
+// Add new migrations to the bottom of the list.
+var migrations = []*Migration{}
+
+// GetCurrentDBVersion returns the current Forgejo database version.
+func GetCurrentDBVersion(x *xorm.Engine) (int64, error) {
+	if err := x.Sync(new(ForgejoVersion)); err != nil {
+		return -1, fmt.Errorf("sync: %w", err)
+	}
+
+	currentVersion := &ForgejoVersion{ID: 1}
+	has, err := x.Get(currentVersion)
+	if err != nil {
+		return -1, fmt.Errorf("get: %w", err)
+	}
+	if !has {
+		return -1, nil
+	}
+	return currentVersion.Version, nil
+}
+
+// ExpectedVersion returns the expected Forgejo database version.
+func ExpectedVersion() int64 {
+	return int64(len(migrations))
+}
+
+// EnsureUpToDate will check if the Forgejo database is at the correct version.
+func EnsureUpToDate(x *xorm.Engine) error {
+	currentDB, err := GetCurrentDBVersion(x)
+	if err != nil {
+		return err
+	}
+
+	if currentDB < 0 {
+		return fmt.Errorf("database has not been initialized")
+	}
+
+	expected := ExpectedVersion()
+
+	if currentDB != expected {
+		return fmt.Errorf(`current Forgejo database version %d is not equal to the expected version %d. Please run "forgejo [--config /path/to/app.ini] migrate" to update the database version`, currentDB, expected)
+	}
+
+	return nil
+}
+
+// Migrate Forgejo database to current version.
+func Migrate(x *xorm.Engine) error {
+	// Set a new clean the default mapper to GonicMapper as that is the default for .
+	x.SetMapper(names.GonicMapper{})
+	if err := x.Sync(new(ForgejoVersion)); err != nil {
+		return fmt.Errorf("sync: %w", err)
+	}
+
+	currentVersion := &ForgejoVersion{ID: 1}
+	has, err := x.Get(currentVersion)
+	if err != nil {
+		return fmt.Errorf("get: %w", err)
+	} else if !has {
+		// If the version record does not exist we think
+		// it is a fresh installation and we can skip all migrations.
+		currentVersion.ID = 0
+		currentVersion.Version = ExpectedVersion()
+
+		if _, err = x.InsertOne(currentVersion); err != nil {
+			return fmt.Errorf("insert: %w", err)
+		}
+	}
+
+	v := currentVersion.Version
+
+	// Downgrading Forgejo's database version not supported
+	if v > ExpectedVersion() {
+		msg := fmt.Sprintf("Your Forgejo database (migration version: %d) is for a newer version of Forgejo, you cannot use the newer database for this old Forgejo release (%d).", v, ExpectedVersion())
+		msg += "\nForgejo will exit to keep your database safe and unchanged. Please use the correct Forgejo release, do not change the migration version manually (incorrect manual operation may cause data loss)."
+		if !setting.IsProd {
+			msg += fmt.Sprintf("\nIf you are in development and really know what you're doing, you can force changing the migration version by executing: UPDATE forgejo_version SET version=%d WHERE id=1;", ExpectedVersion())
+		}
+		_, _ = fmt.Fprintln(os.Stderr, msg)
+		log.Fatal(msg)
+		return nil
+	}
+
+	// Some migration tasks depend on the git command
+	if git.DefaultContext == nil {
+		if err = git.InitSimple(context.Background()); err != nil {
+			return err
+		}
+	}
+
+	// Migrate
+	for i, m := range migrations[v:] {
+		log.Info("Migration[%d]: %s", v+int64(i), m.description)
+		// Reset the mapper between each migration - migrations are not supposed to depend on each other
+		x.SetMapper(names.GonicMapper{})
+		if err = m.migrate(x); err != nil {
+			return fmt.Errorf("migration[%d]: %s failed: %w", v+int64(i), m.description, err)
+		}
+		currentVersion.Version = v + int64(i) + 1
+		if _, err = x.ID(1).Update(currentVersion); err != nil {
+			return err
+		}
+	}
+	return nil
+}

models/migrations/migrations.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"os"
 
+	"code.gitea.io/gitea/models/forgejo_migrations"
 	"code.gitea.io/gitea/models/migrations/v1_10"
 	"code.gitea.io/gitea/models/migrations/v1_11"
 	"code.gitea.io/gitea/models/migrations/v1_12"
@@ -621,5 +622,7 @@ Please try upgrading to a lower version first (suggested v1.6.4), then upgrade t
 			return err
 		}
 	}
-	return nil
+
+	// Execute Forgejo specific migrations.
+	return forgejo_migrations.Migrate(x)
 }