Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_13/v145.go

@@ -0,0 +1,82 @@
+// 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 v1_13 //nolint
+
+import (
+	"fmt"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"xorm.io/xorm"
+)
+
+func IncreaseLanguageField(x *xorm.Engine) error {
+	type LanguageStat struct {
+		RepoID   int64  `xorm:"UNIQUE(s) INDEX NOT NULL"`
+		Language string `xorm:"VARCHAR(50) UNIQUE(s) INDEX NOT NULL"`
+	}
+
+	if err := x.Sync2(new(LanguageStat)); err != nil {
+		return err
+	}
+
+	if setting.Database.UseSQLite3 {
+		// SQLite maps VARCHAR to TEXT without size so we're done
+		return nil
+	}
+
+	// need to get the correct type for the new column
+	inferredTable, err := x.TableInfo(new(LanguageStat))
+	if err != nil {
+		return err
+	}
+	column := inferredTable.GetColumn("language")
+	sqlType := x.Dialect().SQLType(column)
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	switch {
+	case setting.Database.UseMySQL:
+		if _, err := sess.Exec(fmt.Sprintf("ALTER TABLE language_stat MODIFY COLUMN language %s", sqlType)); err != nil {
+			return err
+		}
+	case setting.Database.UseMSSQL:
+		// Yet again MSSQL just has to be awkward.
+		// Here we have to drop the constraints first and then rebuild them
+		constraints := make([]string, 0)
+		if err := sess.SQL(`SELECT i.name AS Name
+			FROM sys.indexes i INNER JOIN sys.index_columns ic
+      			ON i.index_id = ic.index_id AND i.object_id = ic.object_id
+   			INNER JOIN sys.tables AS t
+      			ON t.object_id = i.object_id
+			INNER JOIN sys.columns c
+				ON t.object_id = c.object_id AND ic.column_id = c.column_id
+			WHERE t.name = 'language_stat' AND c.name = 'language'`).Find(&constraints); err != nil {
+			return fmt.Errorf("Find constraints: %w", err)
+		}
+		for _, constraint := range constraints {
+			if _, err := sess.Exec(fmt.Sprintf("DROP INDEX [%s] ON `language_stat`", constraint)); err != nil {
+				return fmt.Errorf("Drop table `language_stat` constraint `%s`: %w", constraint, err)
+			}
+		}
+		if _, err := sess.Exec(fmt.Sprintf("ALTER TABLE language_stat ALTER COLUMN language %s", sqlType)); err != nil {
+			return err
+		}
+		// Finally restore the constraint
+		if err := sess.CreateUniques(new(LanguageStat)); err != nil {
+			return err
+		}
+	case setting.Database.UsePostgreSQL:
+		if _, err := sess.Exec(fmt.Sprintf("ALTER TABLE language_stat ALTER COLUMN language TYPE %s", sqlType)); err != nil {
+			return err
+		}
+	}
+
+	return sess.Commit()
+}