refactor: prepare to decouple the "model migration" package and "models" package (#38533)

Migrations should never use model structs directly, because the model
structs can be different in different releases. e.g. if one migration uses
"User" model, it works in the early releases, then one day, when the
User model changes, the migration breaks because it will use the
new (incorrect) User model, it should only use the old User model.

The same to "modules/structs".

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

modelmigration/fixtures/Test_RemoveInvalidLabels/comment.yml

@@ -0,0 +1,52 @@
+# type Comment struct {
+#   ID      int64 `xorm:"pk autoincr"`
+#   Type    int   `xorm:"INDEX"`
+#   IssueID int64 `xorm:"INDEX"`
+#   LabelID int64
+# }
+#
+# we are only interested in type 7
+#
+
+-
+  id: 1 # Should remain
+  type: 6
+  issue_id: 1
+  label_id: 0
+  should_remain: true
+-
+  id: 2 # Should remain
+  type: 7
+  issue_id: 1 # repo_id: 1
+  label_id: 1 # repo_id: 1
+  should_remain: true
+-
+  id: 3 # Should remain
+  type: 7
+  issue_id: 2 # repo_id: 2 owner_id: 1
+  label_id: 2 # org_id: 1
+  should_remain: true
+-
+  id: 4 # Should be DELETED
+  type: 7
+  issue_id: 1 # repo_id: 1
+  label_id: 3 # repo_id: 2
+  should_remain: false
+-
+  id: 5 # Should remain
+  type: 7
+  issue_id: 3 # repo_id: 1
+  label_id: 1 # repo_id: 1
+  should_remain: true
+-
+  id: 6 # Should be DELETED
+  type: 7
+  issue_id: 3 # repo_id: 1 owner_id: 2
+  label_id: 2 # org_id: 1
+  should_remain: false
+-
+  id: 7 # Should be DELETED
+  type: 7
+  issue_id: 3 # repo_id: 1 owner_id: 2
+  label_id: 5 # repo_id: 3
+  should_remain: false

modelmigration/fixtures/Test_RemoveInvalidLabels/issue.yml

@@ -0,0 +1,21 @@
+# type Issue struct {
+#   ID     int64 `xorm:"pk autoincr"`
+#   RepoID int64 `xorm:"INDEX UNIQUE(repo_index)"`
+#   Index  int64 `xorm:"UNIQUE(repo_index)"` // Index in one repository.
+# }
+-
+  id: 1
+  repo_id: 1
+  index: 1
+-
+  id: 2
+  repo_id: 2
+  index: 1
+-
+  id: 3
+  repo_id: 1
+  index: 2
+-
+  id: 4
+  repo_id: 3
+  index: 1

modelmigration/fixtures/Test_RemoveInvalidLabels/issue_label.yml

@@ -0,0 +1,35 @@
+# type IssueLabel struct {
+#   ID      int64 `xorm:"pk autoincr"`
+#   IssueID int64 `xorm:"UNIQUE(s)"`
+#   LabelID int64 `xorm:"UNIQUE(s)"`
+# }
+-
+  id: 1 # Should remain - matches comment 2
+  issue_id: 1
+  label_id: 1
+  should_remain: true
+-
+  id: 2 # Should remain
+  issue_id: 2
+  label_id: 2
+  should_remain: true
+-
+  id: 3 # Should be deleted
+  issue_id: 1
+  label_id: 3
+  should_remain: false
+-
+  id: 4 # Should remain
+  issue_id: 3
+  label_id: 1
+  should_remain: true
+-
+  id: 5 # Should be deleted
+  issue_id: 3
+  label_id: 2
+  should_remain: false
+-
+  id: 6 # Should be deleted
+  issue_id: 3
+  label_id: 5
+  should_remain: false

modelmigration/fixtures/Test_RemoveInvalidLabels/label.yml

@@ -0,0 +1,25 @@
+# type Label struct {
+#   ID     int64 `xorm:"pk autoincr"`
+#   RepoID int64 `xorm:"INDEX"`
+#   OrgID  int64 `xorm:"INDEX"`
+# }
+-
+  id: 1
+  repo_id: 1
+  org_id: 0
+-
+  id: 2
+  repo_id: 0
+  org_id: 1
+-
+  id: 3
+  repo_id: 2
+  org_id: 0
+-
+  id: 4
+  repo_id: 1
+  org_id: 0
+-
+  id: 5
+  repo_id: 3
+  org_id: 0

modelmigration/fixtures/Test_RemoveInvalidLabels/repository.yml

@@ -0,0 +1,17 @@
+# type Repository struct {
+#   ID        int64  `xorm:"pk autoincr"`
+#   OwnerID   int64  `xorm:"UNIQUE(s) index"`
+#   LowerName string `xorm:"UNIQUE(s) INDEX NOT NULL"`
+# }
+-
+  id: 1
+  owner_id: 2
+  lower_name: "repo1"
+-
+  id: 2
+  owner_id: 1
+  lower_name: "repo2"
+-
+  id: 3
+  owner_id: 2
+  lower_name: "repo3"