Detect broken git hooks

options/locale/locale_en-US.ini

@@ -2643,6 +2643,7 @@ find_file.no_matching = No matching file found
 error.csv.too_large = Can't render this file because it is too large.
 error.csv.unexpected = Can't render this file because it contains an unexpected character in line %d and column %d.
 error.csv.invalid_field_count = Can't render this file because it has a wrong number of fields in line %d.
+error.broken_git_hook = Git hooks of this repository seem to be broken. Please follow the <a target="_blank" rel="noreferrer" href="%s">documentation</a> to fix them, then push some commits to refresh the status.
 
 [graphs]
 component_loading = Loading %s...

routers/web/repo/view.go

@@ -998,6 +998,8 @@ func renderHomeCode(ctx *context.Context) {
 		return
 	}
 
+	checkOutdatedBranch(ctx)
+
 	checkCitationFile(ctx, entry)
 	if ctx.Written() {
 		return
@@ -1064,6 +1066,31 @@ func renderHomeCode(ctx *context.Context) {
 	ctx.HTML(http.StatusOK, tplRepoHome)
 }
 
+func checkOutdatedBranch(ctx *context.Context) {
+	if !(ctx.Repo.IsAdmin() || ctx.Repo.IsOwner()) {
+		return
+	}
+
+	// get the head commit of the branch since ctx.Repo.CommitID is not always the head commit of `ctx.Repo.BranchName`
+	commit, err := ctx.Repo.GitRepo.GetBranchCommit(ctx.Repo.BranchName)
+	if err != nil {
+		log.Error("GetBranchCommitID: %v", err)
+		// Don't return an error page, as it can be rechecked the next time the user opens the page.
+		return
+	}
+
+	dbBranch, err := git_model.GetBranch(ctx, ctx.Repo.Repository.ID, ctx.Repo.BranchName)
+	if err != nil {
+		log.Error("GetBranch: %v", err)
+		// Don't return an error page, as it can be rechecked the next time the user opens the page.
+		return
+	}
+
+	if dbBranch.CommitID != commit.ID.String() {
+		ctx.Flash.Warning(ctx.Tr("repo.error.broken_git_hook", "https://docs.gitea.com/help/faq#push-hook--webhook--actions-arent-running"), true)
+	}
+}
+
 // RenderUserCards render a page show users according the input template
 func RenderUserCards(ctx *context.Context, total int, getter func(opts db.ListOptions) ([]*user_model.User, error), tpl base.TplName) {
 	page := ctx.FormInt("page")