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>

4 files changed, 52 insertions, 18 deletions

diff --git a/routers/web/repo/compare.go b/routers/web/repo/compare.go
index 9f7bef43ef..7721507bae 100644
--- a/routers/web/repo/compare.go
+++ b/routers/web/repo/compare.go
@@ -398,6 +398,7 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 	}
 
 	ctx.Data["HeadRepo"] = ci.HeadRepo
+	ctx.Data["BaseCompareRepo"] = ctx.Repo.Repository
 
 	// Now we need to assert that the ctx.Doer has permission to read
 	// the baseRepo's code and pulls
@@ -436,6 +437,7 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 			ctx.NotFound("ParseCompareInfo", nil)
 			return nil
 		}
+		ctx.Data["CanWriteToHeadRepo"] = permHead.CanWrite(unit.TypeCode)
 	}
 
 	// If we have a rootRepo and it's different from:
diff --git a/routers/web/repo/issue.go b/routers/web/repo/issue.go
index 8e865e448f..a54ad3306b 100644
--- a/routers/web/repo/issue.go
+++ b/routers/web/repo/issue.go
@@ -1529,7 +1529,7 @@ func ViewIssue(ctx *context.Context) {
 		if ctx.IsSigned {
 			if err := pull.LoadHeadRepoCtx(ctx); err != nil {
 				log.Error("LoadHeadRepo: %v", err)
-			} else if pull.HeadRepo != nil && pull.HeadBranch != pull.HeadRepo.DefaultBranch {
+			} else if pull.HeadRepo != nil {
 				perm, err := models.GetUserRepoPermission(ctx, pull.HeadRepo, ctx.Doer)
 				if err != nil {
 					ctx.ServerError("GetUserRepoPermission", err)
@@ -1537,12 +1537,15 @@ func ViewIssue(ctx *context.Context) {
 				}
 				if perm.CanWrite(unit.TypeCode) {
 					// Check if branch is not protected
-					if protected, err := models.IsProtectedBranch(pull.HeadRepo.ID, pull.HeadBranch); err != nil {
-						log.Error("IsProtectedBranch: %v", err)
-					} else if !protected {
-						canDelete = true
-						ctx.Data["DeleteBranchLink"] = issue.Link() + "/cleanup"
+					if pull.HeadBranch != pull.HeadRepo.DefaultBranch {
+						if protected, err := models.IsProtectedBranch(pull.HeadRepo.ID, pull.HeadBranch); err != nil {
+							log.Error("IsProtectedBranch: %v", err)
+						} else if !protected {
+							canDelete = true
+							ctx.Data["DeleteBranchLink"] = issue.Link() + "/cleanup"
+						}
 					}
+					ctx.Data["CanWriteToHeadRepo"] = true
 				}
 			}
 
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,
+	})
+}
diff --git a/routers/web/repo/view.go b/routers/web/repo/view.go
index 168927d101..86fc36fad7 100644
--- a/routers/web/repo/view.go
+++ b/routers/web/repo/view.go
@@ -579,7 +579,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 			ctx.Data["LineEscapeStatus"] = statuses
 		}
 		if !isLFSFile {
-			if ctx.Repo.CanEnableEditor() {
+			if ctx.Repo.CanEnableEditor(ctx.Doer) {
 				if lfsLock != nil && lfsLock.OwnerID != ctx.Doer.ID {
 					ctx.Data["CanEditFile"] = false
 					ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.this_file_locked")
@@ -589,7 +589,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 				}
 			} else if !ctx.Repo.IsViewBranch {
 				ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.must_be_on_a_branch")
-			} else if !ctx.Repo.CanWrite(unit_model.TypeCode) {
+			} else if !ctx.Repo.CanWriteToBranch(ctx.Doer, ctx.Repo.BranchName) {
 				ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.fork_before_edit")
 			}
 		}
@@ -629,7 +629,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 		}
 	}
 
-	if ctx.Repo.CanEnableEditor() {
+	if ctx.Repo.CanEnableEditor(ctx.Doer) {
 		if lfsLock != nil && lfsLock.OwnerID != ctx.Doer.ID {
 			ctx.Data["CanDeleteFile"] = false
 			ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.this_file_locked")
@@ -639,7 +639,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 		}
 	} else if !ctx.Repo.IsViewBranch {
 		ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.must_be_on_a_branch")
-	} else if !ctx.Repo.CanWrite(unit_model.TypeCode) {
+	} else if !ctx.Repo.CanWriteToBranch(ctx.Doer, ctx.Repo.BranchName) {
 		ctx.Data["DeleteFileTooltip"] = ctx.Tr("repo.editor.must_have_write_access")
 	}
 }