Support "merge upstream branch" (Sync fork) (#32741)

Add basic "sync fork" support (GitHub-like)

<details>

![image](https://github.com/user-attachments/assets/e71473f4-4518-48c7-b9e2-fedfcd564fc3)

</details>

10 files changed, 323 insertions, 136 deletions

diff --git a/modules/git/repo.go b/modules/git/repo.go
index 1c223018ad..fc6e6e7acc 100644
--- a/modules/git/repo.go
+++ b/modules/git/repo.go
@@ -223,7 +223,7 @@ func Push(ctx context.Context, repoPath string, opts PushOptions) error {
 	if err != nil {
 		if strings.Contains(stderr, "non-fast-forward") {
 			return &ErrPushOutOfDate{StdOut: stdout, StdErr: stderr, Err: err}
-		} else if strings.Contains(stderr, "! [remote rejected]") {
+		} else if strings.Contains(stderr, "! [remote rejected]") || strings.Contains(stderr, "! [rejected]") {
 			err := &ErrPushRejected{StdOut: stdout, StdErr: stderr, Err: err}
 			err.GenerateMessage()
 			return err
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index e4b8beeeff..1c56dce822 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -1946,6 +1946,10 @@ pulls.delete.title = Delete this pull request?
 pulls.delete.text = Do you really want to delete this pull request? (This will permanently remove all content. Consider closing it instead, if you intend to keep it archived)
 
 pulls.recently_pushed_new_branches = You pushed on branch <strong>%[1]s</strong> %[2]s
+pulls.upstream_diverging_prompt_behind_1 = This branch is %d commit behind %s
+pulls.upstream_diverging_prompt_behind_n = This branch is %d commits behind %s
+pulls.upstream_diverging_prompt_base_newer = The base branch %s has new changes
+pulls.upstream_diverging_merge = Sync fork
 
 pull.deleted_branch = (deleted):%s
 pull.agit_documentation = Review documentation about AGit
diff --git a/routers/web/repo/branch.go b/routers/web/repo/branch.go
index dc170742b9..c918cd7a72 100644
--- a/routers/web/repo/branch.go
+++ b/routers/web/repo/branch.go
@@ -259,3 +259,20 @@ func CreateBranch(ctx *context.Context) {
 	ctx.Flash.Success(ctx.Tr("repo.branch.create_success", form.NewBranchName))
 	ctx.Redirect(ctx.Repo.RepoLink + "/src/branch/" + util.PathEscapeSegments(form.NewBranchName) + "/" + util.PathEscapeSegments(form.CurrentPath))
 }
+
+func MergeUpstream(ctx *context.Context) {
+	branchName := ctx.FormString("branch")
+	_, err := repo_service.MergeUpstream(ctx, ctx.Doer, ctx.Repo.Repository, branchName)
+	if err != nil {
+		if errors.Is(err, util.ErrNotExist) {
+			ctx.JSONError(ctx.Tr("error.not_found"))
+			return
+		} else if models.IsErrMergeConflicts(err) {
+			ctx.JSONError(ctx.Tr("repo.pulls.merge_conflict"))
+			return
+		}
+		ctx.ServerError("MergeUpstream", err)
+		return
+	}
+	ctx.JSONRedirect("")
+}
diff --git a/routers/web/repo/view_file.go b/routers/web/repo/view_file.go
index 03f394d7d8..17c2821824 100644
--- a/routers/web/repo/view_file.go
+++ b/routers/web/repo/view_file.go
@@ -31,7 +31,7 @@ import (
 	"github.com/nektos/act/pkg/model"
 )
 
-func renderFile(ctx *context.Context, entry *git.TreeEntry) {
+func prepareToRenderFile(ctx *context.Context, entry *git.TreeEntry) {
 	ctx.Data["IsViewFile"] = true
 	ctx.Data["HideRepoInfo"] = true
 	blob := entry.Blob()
diff --git a/routers/web/repo/view_home.go b/routers/web/repo/view_home.go
index d1a50800c1..e0539f53b0 100644
--- a/routers/web/repo/view_home.go
+++ b/routers/web/repo/view_home.go
@@ -4,6 +4,7 @@
 package repo
 
 import (
+	"errors"
 	"fmt"
 	"html/template"
 	"net/http"
@@ -86,29 +87,31 @@ func prepareOpenWithEditorApps(ctx *context.Context) {
 	ctx.Data["OpenWithEditorApps"] = tmplApps
 }
 
-func prepareHomeSidebarCitationFile(ctx *context.Context, entry *git.TreeEntry) {
-	if entry.Name() != "" {
-		return
-	}
-	tree, err := ctx.Repo.Commit.SubTree(ctx.Repo.TreePath)
-	if err != nil {
-		HandleGitError(ctx, "Repo.Commit.SubTree", err)
-		return
-	}
-	allEntries, err := tree.ListEntries()
-	if err != nil {
-		ctx.ServerError("ListEntries", err)
-		return
-	}
-	for _, entry := range allEntries {
-		if entry.Name() == "CITATION.cff" || entry.Name() == "CITATION.bib" {
-			// Read Citation file contents
-			if content, err := entry.Blob().GetBlobContent(setting.UI.MaxDisplayFileSize); err != nil {
-				log.Error("checkCitationFile: GetBlobContent: %v", err)
-			} else {
-				ctx.Data["CitiationExist"] = true
-				ctx.PageData["citationFileContent"] = content
-				break
+func prepareHomeSidebarCitationFile(entry *git.TreeEntry) func(ctx *context.Context) {
+	return func(ctx *context.Context) {
+		if entry.Name() != "" {
+			return
+		}
+		tree, err := ctx.Repo.Commit.SubTree(ctx.Repo.TreePath)
+		if err != nil {
+			HandleGitError(ctx, "Repo.Commit.SubTree", err)
+			return
+		}
+		allEntries, err := tree.ListEntries()
+		if err != nil {
+			ctx.ServerError("ListEntries", err)
+			return
+		}
+		for _, entry := range allEntries {
+			if entry.Name() == "CITATION.cff" || entry.Name() == "CITATION.bib" {
+				// Read Citation file contents
+				if content, err := entry.Blob().GetBlobContent(setting.UI.MaxDisplayFileSize); err != nil {
+					log.Error("checkCitationFile: GetBlobContent: %v", err)
+				} else {
+					ctx.Data["CitiationExist"] = true
+					ctx.PageData["citationFileContent"] = content
+					break
+				}
 			}
 		}
 	}
@@ -174,83 +177,21 @@ func prepareHomeSidebarLatestRelease(ctx *context.Context) {
 	}
 }
 
-func renderHomeCode(ctx *context.Context) {
-	ctx.Data["PageIsViewCode"] = true
-	ctx.Data["RepositoryUploadEnabled"] = setting.Repository.Upload.Enabled
-	prepareOpenWithEditorApps(ctx)
-
-	if ctx.Repo.Commit == nil || ctx.Repo.Repository.IsEmpty || ctx.Repo.Repository.IsBroken() {
-		showEmpty := true
-		var err error
-		if ctx.Repo.GitRepo != nil {
-			showEmpty, err = ctx.Repo.GitRepo.IsEmpty()
-			if err != nil {
-				log.Error("GitRepo.IsEmpty: %v", err)
-				ctx.Repo.Repository.Status = repo_model.RepositoryBroken
-				showEmpty = true
-				ctx.Flash.Error(ctx.Tr("error.occurred"), true)
-			}
-		}
-		if showEmpty {
-			ctx.HTML(http.StatusOK, tplRepoEMPTY)
-			return
-		}
-
-		// the repo is not really empty, so we should update the modal in database
-		// such problem may be caused by:
-		// 1) an error occurs during pushing/receiving.  2) the user replaces an empty git repo manually
-		// and even more: the IsEmpty flag is deeply broken and should be removed with the UI changed to manage to cope with empty repos.
-		// it's possible for a repository to be non-empty by that flag but still 500
-		// because there are no branches - only tags -or the default branch is non-extant as it has been 0-pushed.
-		ctx.Repo.Repository.IsEmpty = false
-		if err = repo_model.UpdateRepositoryCols(ctx, ctx.Repo.Repository, "is_empty"); err != nil {
-			ctx.ServerError("UpdateRepositoryCols", err)
-			return
-		}
-		if err = repo_module.UpdateRepoSize(ctx, ctx.Repo.Repository); err != nil {
-			ctx.ServerError("UpdateRepoSize", err)
-			return
-		}
-
-		// the repo's IsEmpty has been updated, redirect to this page to make sure middlewares can get the correct values
-		link := ctx.Link
-		if ctx.Req.URL.RawQuery != "" {
-			link += "?" + ctx.Req.URL.RawQuery
-		}
-		ctx.Redirect(link)
-		return
-	}
-
-	title := ctx.Repo.Repository.Owner.Name + "/" + ctx.Repo.Repository.Name
-	if len(ctx.Repo.Repository.Description) > 0 {
-		title += ": " + ctx.Repo.Repository.Description
-	}
-	ctx.Data["Title"] = title
-
-	// Get Topics of this repo
-	prepareHomeSidebarRepoTopics(ctx)
-	if ctx.Written() {
+func prepareUpstreamDivergingInfo(ctx *context.Context) {
+	if !ctx.Repo.Repository.IsFork || !ctx.Repo.IsViewBranch || ctx.Repo.TreePath != "" {
 		return
 	}
-
-	// Get current entry user currently looking at.
-	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
+	upstreamDivergingInfo, err := repo_service.GetUpstreamDivergingInfo(ctx, ctx.Repo.Repository, ctx.Repo.BranchName)
 	if err != nil {
-		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
-		return
-	}
-
-	checkOutdatedBranch(ctx)
-
-	if entry.IsDir() {
-		prepareToRenderDirectory(ctx)
-	} else {
-		renderFile(ctx, entry)
-	}
-	if ctx.Written() {
+		if !errors.Is(err, util.ErrNotExist) && !errors.Is(err, util.ErrInvalidArgument) {
+			log.Error("GetUpstreamDivergingInfo: %v", err)
+		}
 		return
 	}
+	ctx.Data["UpstreamDivergingInfo"] = upstreamDivergingInfo
+}
 
+func prepareRecentlyPushedNewBranches(ctx *context.Context) {
 	if ctx.Doer != nil {
 		if err := ctx.Repo.Repository.GetBaseRepo(ctx); err != nil {
 			ctx.ServerError("GetBaseRepo", err)
@@ -280,53 +221,60 @@ func renderHomeCode(ctx *context.Context) {
 			}
 		}
 	}
+}
 
-	var treeNames, paths []string
-	branchLink := ctx.Repo.RepoLink + "/src/" + ctx.Repo.BranchNameSubURL()
-	treeLink := branchLink
-	if ctx.Repo.TreePath != "" {
-		treeLink += "/" + util.PathEscapeSegments(ctx.Repo.TreePath)
-		treeNames = strings.Split(ctx.Repo.TreePath, "/")
-		for i := range treeNames {
-			paths = append(paths, strings.Join(treeNames[:i+1], "/"))
-		}
-		ctx.Data["HasParentPath"] = true
-		if len(paths)-2 >= 0 {
-			ctx.Data["ParentPath"] = "/" + paths[len(paths)-2]
+func handleRepoEmptyOrBroken(ctx *context.Context) {
+	showEmpty := true
+	var err error
+	if ctx.Repo.GitRepo != nil {
+		showEmpty, err = ctx.Repo.GitRepo.IsEmpty()
+		if err != nil {
+			log.Error("GitRepo.IsEmpty: %v", err)
+			ctx.Repo.Repository.Status = repo_model.RepositoryBroken
+			showEmpty = true
+			ctx.Flash.Error(ctx.Tr("error.occurred"), true)
 		}
 	}
+	if showEmpty {
+		ctx.HTML(http.StatusOK, tplRepoEMPTY)
+		return
+	}
 
-	isTreePathRoot := ctx.Repo.TreePath == ""
-	if isTreePathRoot {
-		prepareHomeSidebarLicenses(ctx)
-		if ctx.Written() {
-			return
-		}
-		prepareHomeSidebarCitationFile(ctx, entry)
-		if ctx.Written() {
-			return
-		}
+	// the repo is not really empty, so we should update the modal in database
+	// such problem may be caused by:
+	// 1) an error occurs during pushing/receiving.  2) the user replaces an empty git repo manually
+	// and even more: the IsEmpty flag is deeply broken and should be removed with the UI changed to manage to cope with empty repos.
+	// it's possible for a repository to be non-empty by that flag but still 500
+	// because there are no branches - only tags -or the default branch is non-extant as it has been 0-pushed.
+	ctx.Repo.Repository.IsEmpty = false
+	if err = repo_model.UpdateRepositoryCols(ctx, ctx.Repo.Repository, "is_empty"); err != nil {
+		ctx.ServerError("UpdateRepositoryCols", err)
+		return
+	}
+	if err = repo_module.UpdateRepoSize(ctx, ctx.Repo.Repository); err != nil {
+		ctx.ServerError("UpdateRepoSize", err)
+		return
+	}
 
-		prepareHomeSidebarLanguageStats(ctx)
-		if ctx.Written() {
-			return
-		}
+	// the repo's IsEmpty has been updated, redirect to this page to make sure middlewares can get the correct values
+	link := ctx.Link
+	if ctx.Req.URL.RawQuery != "" {
+		link += "?" + ctx.Req.URL.RawQuery
+	}
+	ctx.Redirect(link)
+}
 
-		prepareHomeSidebarLatestRelease(ctx)
-		if ctx.Written() {
-			return
+func prepareToRenderDirOrFile(entry *git.TreeEntry) func(ctx *context.Context) {
+	return func(ctx *context.Context) {
+		if entry.IsDir() {
+			prepareToRenderDirectory(ctx)
+		} else {
+			prepareToRenderFile(ctx, entry)
 		}
 	}
-
-	ctx.Data["Paths"] = paths
-	ctx.Data["TreeLink"] = treeLink
-	ctx.Data["TreeNames"] = treeNames
-	ctx.Data["BranchLink"] = branchLink
-	ctx.HTML(http.StatusOK, tplRepoHome)
 }
 
-// Home render repository home page
-func Home(ctx *context.Context) {
+func handleRepoHomeFeed(ctx *context.Context) bool {
 	if setting.Other.EnableFeed {
 		isFeed, _, showFeedType := feed.GetFeedType(ctx.PathParam(":reponame"), ctx.Req)
 		if isFeed {
@@ -338,14 +286,93 @@ func Home(ctx *context.Context) {
 			case ctx.Repo.TreePath != "":
 				feed.ShowFileFeed(ctx, ctx.Repo.Repository, showFeedType)
 			}
-			return
+			return true
 		}
 	}
+	return false
+}
+
+// Home render repository home page
+func Home(ctx *context.Context) {
+	if handleRepoHomeFeed(ctx) {
+		return
+	}
 
+	// Check whether the repo is viewable: not in migration, and the code unit should be enabled
+	// Ideally the "feed" logic should be after this, but old code did so, so keep it as-is.
 	checkHomeCodeViewable(ctx)
 	if ctx.Written() {
 		return
 	}
 
-	renderHomeCode(ctx)
+	title := ctx.Repo.Repository.Owner.Name + "/" + ctx.Repo.Repository.Name
+	if len(ctx.Repo.Repository.Description) > 0 {
+		title += ": " + ctx.Repo.Repository.Description
+	}
+	ctx.Data["Title"] = title
+	ctx.Data["PageIsViewCode"] = true
+	ctx.Data["RepositoryUploadEnabled"] = setting.Repository.Upload.Enabled // show New File / Upload File buttons
+
+	if ctx.Repo.Commit == nil || ctx.Repo.Repository.IsEmpty || ctx.Repo.Repository.IsBroken() {
+		// empty or broken repositories need to be handled differently
+		handleRepoEmptyOrBroken(ctx)
+		return
+	}
+
+	// get the current git entry which doer user is currently looking at.
+	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
+	if err != nil {
+		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
+		return
+	}
+
+	// prepare the tree path
+	var treeNames, paths []string
+	branchLink := ctx.Repo.RepoLink + "/src/" + ctx.Repo.BranchNameSubURL()
+	treeLink := branchLink
+	if ctx.Repo.TreePath != "" {
+		treeLink += "/" + util.PathEscapeSegments(ctx.Repo.TreePath)
+		treeNames = strings.Split(ctx.Repo.TreePath, "/")
+		for i := range treeNames {
+			paths = append(paths, strings.Join(treeNames[:i+1], "/"))
+		}
+		ctx.Data["HasParentPath"] = true
+		if len(paths)-2 >= 0 {
+			ctx.Data["ParentPath"] = "/" + paths[len(paths)-2]
+		}
+	}
+	ctx.Data["Paths"] = paths
+	ctx.Data["TreeLink"] = treeLink
+	ctx.Data["TreeNames"] = treeNames
+	ctx.Data["BranchLink"] = branchLink
+
+	// some UI components are only shown when the tree path is root
+	isTreePathRoot := ctx.Repo.TreePath == ""
+
+	prepareFuncs := []func(*context.Context){
+		prepareOpenWithEditorApps,
+		prepareHomeSidebarRepoTopics,
+		checkOutdatedBranch,
+		prepareToRenderDirOrFile(entry),
+		prepareRecentlyPushedNewBranches,
+	}
+
+	if isTreePathRoot {
+		prepareFuncs = append(prepareFuncs,
+			prepareUpstreamDivergingInfo,
+			prepareHomeSidebarLicenses,
+			prepareHomeSidebarCitationFile(entry),
+			prepareHomeSidebarLanguageStats,
+			prepareHomeSidebarLatestRelease,
+		)
+	}
+
+	for _, prepare := range prepareFuncs {
+		prepare(ctx)
+		if ctx.Written() {
+			return
+		}
+	}
+
+	ctx.HTML(http.StatusOK, tplRepoHome)
 }
diff --git a/routers/web/web.go b/routers/web/web.go
index 85e0fdc41e..c87c01ea0f 100644
--- a/routers/web/web.go
+++ b/routers/web/web.go
@@ -1320,6 +1320,7 @@ func registerRoutes(m *web.Router) {
 			m.Post("/delete", repo.DeleteBranchPost)
 			m.Post("/restore", repo.RestoreBranchPost)
 			m.Post("/rename", web.Bind(forms.RenameBranchForm{}), repo_setting.RenameBranchPost)
+			m.Post("/merge-upstream", repo.MergeUpstream)
 		}, context.RepoMustNotBeArchived(), reqRepoCodeWriter, repo.MustBeNotEmpty)
 
 		m.Combo("/fork").Get(repo.Fork).Post(web.Bind(forms.CreateRepoForm{}), repo.ForkPost)
diff --git a/services/pull/update.go b/services/pull/update.go
index 311ffc2442..abf7ad4509 100644
--- a/services/pull/update.go
+++ b/services/pull/update.go
@@ -65,7 +65,9 @@ func Update(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.
 		return fmt.Errorf("unable to load HeadRepo for PR[%d] during update-by-merge: %w", pr.ID, err)
 	}
 
-	// use merge functions but switch repos and branches
+	// TODO: FakePR: it is somewhat hacky, but it is the only way to "merge" at the moment
+	// ideally in the future the "merge" functions should be refactored to decouple from the PullRequest
+	// now use a fake reverse PR to switch head&base repos/branches
 	reversePR := &issues_model.PullRequest{
 		ID: pr.ID,
 
diff --git a/services/repository/merge_upstream.go b/services/repository/merge_upstream.go
new file mode 100644
index 0000000000..85ca8f7e31
--- /dev/null
+++ b/services/repository/merge_upstream.go
@@ -0,0 +1,115 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repository
+
+import (
+	"context"
+	"fmt"
+
+	git_model "code.gitea.io/gitea/models/git"
+	issue_model "code.gitea.io/gitea/models/issues"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/git"
+	repo_module "code.gitea.io/gitea/modules/repository"
+	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/services/pull"
+)
+
+type UpstreamDivergingInfo struct {
+	BaseIsNewer   bool
+	CommitsBehind int
+	CommitsAhead  int
+}
+
+func MergeUpstream(ctx context.Context, doer *user_model.User, repo *repo_model.Repository, branch string) (mergeStyle string, err error) {
+	if err = repo.MustNotBeArchived(); err != nil {
+		return "", err
+	}
+	if err = repo.GetBaseRepo(ctx); err != nil {
+		return "", err
+	}
+	err = git.Push(ctx, repo.BaseRepo.RepoPath(), git.PushOptions{
+		Remote: repo.RepoPath(),
+		Branch: fmt.Sprintf("%s:%s", branch, branch),
+		Env:    repo_module.PushingEnvironment(doer, repo),
+	})
+	if err == nil {
+		return "fast-forward", nil
+	}
+	if !git.IsErrPushOutOfDate(err) && !git.IsErrPushRejected(err) {
+		return "", err
+	}
+
+	// TODO: FakePR: it is somewhat hacky, but it is the only way to "merge" at the moment
+	// ideally in the future the "merge" functions should be refactored to decouple from the PullRequest
+	fakeIssue := &issue_model.Issue{
+		ID:       -1,
+		RepoID:   repo.ID,
+		Repo:     repo,
+		Index:    -1,
+		PosterID: doer.ID,
+		Poster:   doer,
+		IsPull:   true,
+	}
+	fakePR := &issue_model.PullRequest{
+		ID:         -1,
+		Status:     issue_model.PullRequestStatusMergeable,
+		IssueID:    -1,
+		Issue:      fakeIssue,
+		Index:      -1,
+		HeadRepoID: repo.ID,
+		HeadRepo:   repo,
+		BaseRepoID: repo.BaseRepo.ID,
+		BaseRepo:   repo.BaseRepo,
+		HeadBranch: branch, // maybe HeadCommitID is not needed
+		BaseBranch: branch,
+	}
+	fakeIssue.PullRequest = fakePR
+	err = pull.Update(ctx, fakePR, doer, "merge upstream", false)
+	if err != nil {
+		return "", err
+	}
+	return "merge", nil
+}
+
+func GetUpstreamDivergingInfo(ctx context.Context, repo *repo_model.Repository, branch string) (*UpstreamDivergingInfo, error) {
+	if !repo.IsFork {
+		return nil, util.NewInvalidArgumentErrorf("repo is not a fork")
+	}
+
+	if repo.IsArchived {
+		return nil, util.NewInvalidArgumentErrorf("repo is archived")
+	}
+
+	if err := repo.GetBaseRepo(ctx); err != nil {
+		return nil, err
+	}
+
+	forkBranch, err := git_model.GetBranch(ctx, repo.ID, branch)
+	if err != nil {
+		return nil, err
+	}
+
+	baseBranch, err := git_model.GetBranch(ctx, repo.BaseRepo.ID, branch)
+	if err != nil {
+		return nil, err
+	}
+
+	info := &UpstreamDivergingInfo{}
+	if forkBranch.CommitID == baseBranch.CommitID {
+		return info, nil
+	}
+
+	// TODO: if the fork repo has new commits, this call will fail:
+	// exit status 128 - fatal: Invalid symmetric difference expression aaaaaaaaaaaa...bbbbbbbbbbbb
+	// so at the moment, we are not able to handle this case, should be improved in the future
+	diff, err := git.GetDivergingCommits(ctx, repo.BaseRepo.RepoPath(), baseBranch.CommitID, forkBranch.CommitID)
+	if err != nil {
+		info.BaseIsNewer = baseBranch.UpdatedUnix > forkBranch.UpdatedUnix
+		return info, nil
+	}
+	info.CommitsBehind, info.CommitsAhead = diff.Behind, diff.Ahead
+	return info, nil
+}
diff --git a/templates/repo/code/upstream_diverging_info.tmpl b/templates/repo/code/upstream_diverging_info.tmpl
new file mode 100644
index 0000000000..299ba63e9e
--- /dev/null
+++ b/templates/repo/code/upstream_diverging_info.tmpl
@@ -0,0 +1,18 @@
+{{if and .UpstreamDivergingInfo (or .UpstreamDivergingInfo.BaseIsNewer .UpstreamDivergingInfo.CommitsBehind)}}
+<div class="ui message flex-text-block">
+	<div class="tw-flex-1">
+		{{$upstreamLink := printf "%s/src/branch/%s" .Repository.BaseRepo.Link (.BranchName|PathEscapeSegments)}}
+		{{$upstreamHtml := HTMLFormat `<a href="%s">%s:%s</a>` $upstreamLink .Repository.BaseRepo.FullName .BranchName}}
+		{{if .UpstreamDivergingInfo.CommitsBehind}}
+			{{ctx.Locale.TrN .UpstreamDivergingInfo.CommitsBehind "repo.pulls.upstream_diverging_prompt_behind_1" "repo.pulls.upstream_diverging_prompt_behind_n" .UpstreamDivergingInfo.CommitsBehind $upstreamHtml}}
+		{{else}}
+			{{ctx.Locale.Tr "repo.pulls.upstream_diverging_prompt_base_newer" $upstreamHtml}}
+		{{end}}
+	</div>
+	{{if .CanWriteCode}}
+	<button class="ui compact green button tw-m-0 link-action" data-url="{{.Repository.Link}}/branches/merge-upstream?branch={{.BranchName}}">
+		{{ctx.Locale.Tr "repo.pulls.upstream_diverging_merge"}}
+	</button>
+	{{end}}
+</div>
+{{end}}
diff --git a/templates/repo/home.tmpl b/templates/repo/home.tmpl
index 63bf3eef0f..343425134b 100644
--- a/templates/repo/home.tmpl
+++ b/templates/repo/home.tmpl
@@ -136,6 +136,9 @@
 				{{else if .IsBlame}}
 					{{template "repo/blame" .}}
 				{{else}}{{/* IsViewDirectory */}}
+					{{if $isTreePathRoot}}
+						{{template "repo/code/upstream_diverging_info" .}}
+					{{end}}
 					{{template "repo/view_list" .}}
 				{{end}}
 			</div>