allow user fork repo even when as a guest.. This will prompt the user to login and if authentication was successful, the user will be redirected to fork the repo (#5690)

options/locale/locale_en-US.ini

@@ -561,6 +561,7 @@ migrate.lfs_mirror_unsupported = Mirroring LFS objects is not supported - use 'g
 mirror_from = mirror of
 forked_from = forked from
 fork_from_self = You cannot fork a repository you own.
+fork_guest_user = Sign in to fork this repository.
 copy_link = Copy
 copy_link_success = Link has been copied
 copy_link_error = Use ⌘C or Ctrl-C to copy

templates/repo/header.tmpl

@@ -32,7 +32,7 @@
 				</div>
 				{{if and (not .IsBare) ($.Permission.CanRead $.UnitTypeCode)}}
 					<div class="ui compact labeled button" tabindex="0">
-						<a class="ui compact button {{if not $.CanSignedUserFork}}poping up{{end}}" {{if $.CanSignedUserFork}}href="{{AppSubUrl}}/repo/fork/{{.ID}}"{{else if $.IsSigned}} data-content="{{$.i18n.Tr "repo.fork_from_self"}}" data-position="top center" data-variation="tiny"{{end}}>
+						<a class="ui compact button {{if or (not $.IsSigned) (not $.CanSignedUserFork)}}poping up{{end}}" {{if $.CanSignedUserFork}}href="{{AppSubUrl}}/repo/fork/{{.ID}}"{{else if $.IsSigned}} data-content="{{$.i18n.Tr "repo.fork_from_self"}}" {{ else }} data-content="{{$.i18n.Tr "repo.fork_guest_user" }}" href="{{AppSubUrl}}/user/login?redirect_to={{AppSubUrl}}/repo/fork/{{.ID}}" {{end}} data-position="top center" data-variation="tiny">
 							<i class="octicon octicon-repo-forked"></i>{{$.i18n.Tr "repo.fork"}}
 						</a>
 						<a class="ui basic label" href="{{.Link}}/forks">