Display warning when user try to rename default branch

options/locale/locale_en-US.ini

@@ -2411,6 +2411,7 @@ branch.included_desc = This branch is part of the default branch
 branch.included = Included
 branch.create_new_branch = Create branch from branch:
 branch.confirm_create_branch = Create branch
+branch.warning_raname_default_branch = You are trying to rename default branch.
 branch.rename_branch_to = Rename "%s" to:
 branch.confirm_rename_branch = Rename branch
 branch.create_branch_operation = Create branch

templates/repo/branch/list.tmpl

@@ -52,6 +52,7 @@
 								{{end}}
 								{{if and $.IsWriter (not $.Repository.IsArchived) (not .IsDeleted) (not $.IsMirror)}}
 									<button class="ui tertiary button show-modal show-rename-branch-modal gt-mx-3"
+										data-is-defualt-branch="true"
 										data-modal="#rename-branch-modal"
 										data-old-branch-name="{{$.DefaultBranch}}"
 										data-tooltip-content="{{$.locale.Tr "repo.branch.rename" ($.DefaultBranch)}}"
@@ -158,6 +159,7 @@
 										{{end}}
 										{{if and $.IsWriter (not $.Repository.IsArchived) (not .IsDeleted) (not $.IsMirror)}}
 											<button class="ui tertiary button show-modal show-rename-branch-modal gt-mx-3"
+												data-is-defualt-branch="false"
 												data-old-branch-name="{{.Name}}"
 												data-modal="#rename-branch-modal"
 												data-tooltip-content="{{$.locale.Tr "repo.branch.rename" (.Name)}}"
@@ -229,6 +231,9 @@
 	<form class="ui form" action="{{$.Repository.Link}}/settings/rename_branch" method="post">
 		<div class="content">
 			{{.CsrfTokenHtml}}
+			<div class="field default-branch-warning">
+				<span class="text red">{{.locale.Tr "repo.branch.warning_raname_default_branch"}}</span>
+			</div>
 			<div class="field">
 				<span class="text" data-rename-branch-to="{{.locale.Tr "repo.branch.rename_branch_to"}}"></span>
 			</div>

web_src/js/features/repo-branch.js

@@ -31,6 +31,11 @@ function initRepoRenameBranchButton() {
     const oldBranchName = $(this).attr('data-old-branch-name');
     $modal.find('input[name=from]').val(oldBranchName);
 
+    // display the warning that the branch which is choosen is the default branch
+    const $warn = $modal.find('.default-branch-warning');
+    if ($(this).attr('data-is-defualt-branch') !== 'true') $warn.addClass('gt-hidden');
+    else $warn.removeClass('gt-hidden');
+
     const $text = $modal.find('[data-rename-branch-to]');
     $text.text($text.attr('data-rename-branch-to').replace('%s', oldBranchName));
   });