Improve migrations to support migrating milestones/labels/issues/comments/pullrequests (#6290)

* add migrations

* fix package dependency

* fix lints

* implements migrations except pull requests

* add releases

* migrating releases

* fix bug

* fix lint

* fix migrate releases

* fix tests

* add rollback

* pull request migtations

* fix import

* fix go module vendor

* add tests for upload to gitea

* more migrate options

* fix swagger-check

* fix misspell

* add options on migration UI

* fix log error

* improve UI options on migrating

* add support for username password when migrating from github

* fix tests

* remove comments and fix migrate limitation

* improve error handles

* migrate API will also support migrate milestones/labels/issues/pulls/releases

* fix tests and remove unused codes

* add DownloaderFactory and docs about how to create a new Downloader

* fix misspell

* fix migration docs

* Add hints about migrate options on migration page

* fix tests

vendor/github.com/google/go-github/v24/github/git_trees.go

@@ -0,0 +1,99 @@
+// Copyright 2013 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package github
+
+import (
+	"context"
+	"fmt"
+)
+
+// Tree represents a GitHub tree.
+type Tree struct {
+	SHA     *string     `json:"sha,omitempty"`
+	Entries []TreeEntry `json:"tree,omitempty"`
+
+	// Truncated is true if the number of items in the tree
+	// exceeded GitHub's maximum limit and the Entries were truncated
+	// in the response. Only populated for requests that fetch
+	// trees like Git.GetTree.
+	Truncated *bool `json:"truncated,omitempty"`
+}
+
+func (t Tree) String() string {
+	return Stringify(t)
+}
+
+// TreeEntry represents the contents of a tree structure. TreeEntry can
+// represent either a blob, a commit (in the case of a submodule), or another
+// tree.
+type TreeEntry struct {
+	SHA     *string `json:"sha,omitempty"`
+	Path    *string `json:"path,omitempty"`
+	Mode    *string `json:"mode,omitempty"`
+	Type    *string `json:"type,omitempty"`
+	Size    *int    `json:"size,omitempty"`
+	Content *string `json:"content,omitempty"`
+	URL     *string `json:"url,omitempty"`
+}
+
+func (t TreeEntry) String() string {
+	return Stringify(t)
+}
+
+// GetTree fetches the Tree object for a given sha hash from a repository.
+//
+// GitHub API docs: https://developer.github.com/v3/git/trees/#get-a-tree
+func (s *GitService) GetTree(ctx context.Context, owner string, repo string, sha string, recursive bool) (*Tree, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/git/trees/%v", owner, repo, sha)
+	if recursive {
+		u += "?recursive=1"
+	}
+
+	req, err := s.client.NewRequest("GET", u, nil)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	t := new(Tree)
+	resp, err := s.client.Do(ctx, req, t)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return t, resp, nil
+}
+
+// createTree represents the body of a CreateTree request.
+type createTree struct {
+	BaseTree string      `json:"base_tree,omitempty"`
+	Entries  []TreeEntry `json:"tree"`
+}
+
+// CreateTree creates a new tree in a repository. If both a tree and a nested
+// path modifying that tree are specified, it will overwrite the contents of
+// that tree with the new path contents and write a new tree out.
+//
+// GitHub API docs: https://developer.github.com/v3/git/trees/#create-a-tree
+func (s *GitService) CreateTree(ctx context.Context, owner string, repo string, baseTree string, entries []TreeEntry) (*Tree, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/git/trees", owner, repo)
+
+	body := &createTree{
+		BaseTree: baseTree,
+		Entries:  entries,
+	}
+	req, err := s.client.NewRequest("POST", u, body)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	t := new(Tree)
+	resp, err := s.client.Do(ctx, req, t)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return t, resp, nil
+}