Add option to API to update PullRequest base branch

[6543]

close #11552

[blaggacao]

Failing test seem unrelated?

[blaggacao]

Some things I took from:

gitea/routers/repo/pull.go

Lines 1190 to 1229 in 5cb201d

	if err := pull_service.ChangeTargetBranch(pr, ctx.User, targetBranch); err != nil {
	if models.IsErrPullRequestAlreadyExists(err) {
	err := err.(models.ErrPullRequestAlreadyExists)
	RepoRelPath := ctx.Repo.Owner.Name + "/" + ctx.Repo.Repository.Name
	errorMessage := ctx.Tr("repo.pulls.has_pull_request", ctx.Repo.RepoLink, RepoRelPath, err.IssueID)
	ctx.Flash.Error(errorMessage)
	ctx.JSON(http.StatusConflict, map[string]interface{}{
	"error": err.Error(),
	"user_error": errorMessage,
	})
	} else if models.IsErrIssueIsClosed(err) {
	errorMessage := ctx.Tr("repo.pulls.is_closed")
	ctx.Flash.Error(errorMessage)
	ctx.JSON(http.StatusConflict, map[string]interface{}{
	"error": err.Error(),
	"user_error": errorMessage,
	})
	} else if models.IsErrPullRequestHasMerged(err) {
	errorMessage := ctx.Tr("repo.pulls.has_merged")
	ctx.Flash.Error(errorMessage)
	ctx.JSON(http.StatusConflict, map[string]interface{}{
	"error": err.Error(),
	"user_error": errorMessage,
	})
	} else if models.IsErrBranchesEqual(err) {
	errorMessage := ctx.Tr("repo.pulls.nothing_to_compare")
	ctx.Flash.Error(errorMessage)
	ctx.JSON(http.StatusBadRequest, map[string]interface{}{
	"error": err.Error(),
	"user_error": errorMessage,
	})
	} else {
	ctx.ServerError("UpdatePullRequestTarget", err)
	}
	return

[6543]

updated tests, now all should PASS :D

[lunny]

Is this change compitable with Github API?

[blaggacao]

What I know: Github provides this feature through it's API.

[6543]

@lunny https://developer.github.com/v3/pulls/#input-2

[blaggacao]

@zeripath @lunny Anything is blocking second review? Are code owners summoned?

[blaggacao]

git-town/git-town#1518 has gotten merged, git town now supports gitea, but for full support this PR is pressing, everything else is set up. ⌛ The gun is loaded.

[blaggacao]

@zeripath You marked this for 1.13.0. Given it's blocking git-town/git-town#1530, any chance to get this shipped earlier?

[techknowlogick]

@blaggacao as we've already passed the feature freeze, and are now in the RC phase for 1.12 we cannot get it into the 1.12 release.

[blaggacao]

I see, ok then, let's head for 1.13.0! 🚀

[zeripath]

notwithstanding my comments re:transactions as this doesn't make the function worse I think we can leave that be.

[zeripath]

@techknowlogick it might be reasonable to backport this as you could argue it's a bug that the API doesn't have this when the UI does.

[zeripath]

make lg-tm work

[6543]

Backport = #11796

[blaggacao]

Nice, thank you all!