Add "Allow edits from maintainer" feature (#18002)

Adds a feature [like GitHub has](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork) (step 7).
If you create a new PR from a forked repo, you can select (and change later, but only if you are the PR creator/poster) the "Allow edits from maintainers" option.
Then users with write access to the base branch get more permissions on this branch:
* use the update pull request button
* push directly from the command line (`git push`)
* edit/delete/upload files via web UI
* use related API endpoints

You can't merge PRs to this branch with this enabled, you'll need "full" code write permissions.

This feature has a pretty big impact on the permission system. I might forgot changing some things or didn't find security vulnerabilities. In this case, please leave a review or comment on this PR.

Closes #17728

Co-authored-by: 6543 <6543@obermui.de>

1 files changed, 37 insertions, 8 deletions

diff --git a/routers/web/repo/pull.go b/routers/web/repo/pull.go
index a03e16f39a..99faa54138 100644
--- a/routers/web/repo/pull.go
+++ b/routers/web/repo/pull.go
@@ -1132,14 +1132,15 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 		Content:     form.Content,
 	}
 	pullRequest := &models.PullRequest{
-		HeadRepoID: ci.HeadRepo.ID,
-		BaseRepoID: repo.ID,
-		HeadBranch: ci.HeadBranch,
-		BaseBranch: ci.BaseBranch,
-		HeadRepo:   ci.HeadRepo,
-		BaseRepo:   repo,
-		MergeBase:  ci.CompareInfo.MergeBase,
-		Type:       models.PullRequestGitea,
+		HeadRepoID:          ci.HeadRepo.ID,
+		BaseRepoID:          repo.ID,
+		HeadBranch:          ci.HeadBranch,
+		BaseBranch:          ci.BaseBranch,
+		HeadRepo:            ci.HeadRepo,
+		BaseRepo:            repo,
+		MergeBase:           ci.CompareInfo.MergeBase,
+		Type:                models.PullRequestGitea,
+		AllowMaintainerEdit: form.AllowMaintainerEdit,
 	}
 	// FIXME: check error in the case two people send pull request at almost same time, give nice error prompt
 	// instead of 500.
@@ -1411,3 +1412,31 @@ func UpdatePullRequestTarget(ctx *context.Context) {
 		"base_branch": pr.BaseBranch,
 	})
 }
+
+// SetAllowEdits allow edits from maintainers to PRs
+func SetAllowEdits(ctx *context.Context) {
+	form := web.GetForm(ctx).(*forms.UpdateAllowEditsForm)
+
+	pr, err := models.GetPullRequestByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
+	if err != nil {
+		if models.IsErrPullRequestNotExist(err) {
+			ctx.NotFound("GetPullRequestByIndex", err)
+		} else {
+			ctx.ServerError("GetPullRequestByIndex", err)
+		}
+		return
+	}
+
+	if err := pull_service.SetAllowEdits(ctx, ctx.Doer, pr, form.AllowMaintainerEdit); err != nil {
+		if errors.Is(pull_service.ErrUserHasNoPermissionForAction, err) {
+			ctx.Error(http.StatusForbidden)
+			return
+		}
+		ctx.ServerError("SetAllowEdits", err)
+		return
+	}
+
+	ctx.JSON(http.StatusOK, map[string]interface{}{
+		"allow_maintainer_edit": pr.AllowMaintainerEdit,
+	})
+}