Attempt to fix #6707 (#6823) (#6854)

Author: zeripath

Diff for: models/migrations/v78.go

@@ -32,7 +32,14 @@ func renameRepoIsBareToIsEmpty(x *xorm.Engine) error {
 	if models.DbCfg.Type == core.POSTGRES || models.DbCfg.Type == core.SQLITE {
 		_, err = sess.Exec("DROP INDEX IF EXISTS IDX_repository_is_bare")
 	} else if models.DbCfg.Type == core.MSSQL {
-		_, err = sess.Exec("DROP INDEX IF EXISTS IDX_repository_is_bare ON repository")
+		_, err = sess.Exec(`DECLARE @ConstraintName VARCHAR(256)
+		DECLARE @SQL NVARCHAR(256)
+		SELECT @ConstraintName = obj.name FROM sys.columns col LEFT OUTER JOIN sys.objects obj ON obj.object_id = col.default_object_id AND obj.type = 'D' WHERE col.object_id = OBJECT_ID('repository') AND obj.name IS NOT NULL AND col.name = 'is_bare'
+		SET @SQL = N'ALTER TABLE [repository] DROP CONSTRAINT [' + @ConstraintName + N']'
+		EXEC sp_executesql @SQL`)
+		if err != nil {
+			return err
+		}
 	} else if models.DbCfg.Type == core.MYSQL {
 		indexes, err := sess.QueryString(`SHOW INDEX FROM repository WHERE KEY_NAME = 'IDX_repository_is_bare'`)
 		if err != nil {