Redirect to group boards with params from old path

If using the old path (`/groups/$group/boards/*`), and there is no subgroup
called 'boards', redirect to `/groups/$group/-/boards/*`.

Note that because there is no path matching a group followed by an integer, this
redirect will work for individual boards even if there _is_ a subgroup called
'boards'.

changelogs/unreleased-ee/fix-group-boards-redirect.yml

+---
+title: Redirect to existing group boards using old URL if there is no subgroup called
+  'boards'
+merge_request:
+author:
+type: fixed

config/routes/group.rb

@@ -89,7 +89,14 @@ constraints(GroupUrlConstrainer.new) do
     end
 
     ## EE-specific
-    get :boards, to: redirect('/groups/%{group_id}/-/boards')
+    legacy_ee_group_boards_redirect = redirect do |params, request|
+      path = "/groups/#{params[:group_id]}/-/boards"
+      path << "/#{params[:extra_params]}" if params[:extra_params].present?
+      path << "?#{request.query_string}" if request.query_string.present?
+      path
+    end
+
+    get 'boards(/*extra_params)', as: :legacy_ee_group_boards_redirect, to: legacy_ee_group_boards_redirect
   end
 
   scope(path: '*id',

spec/requests/group_routing_spec.rb

 require 'spec_helper'
 
 describe 'Deprecated boards paths' do
-  it 'redirects to boards page' do
-    group = create :group, name: 'gitlabhq'
+  let!(:group) { create(:group, name: 'gitlabhq') }
 
-    get('/groups/gitlabhq/boards')
+  context 'when no group called boards exists' do
+    it 'redirects to boards page' do
+      get('/groups/gitlabhq/boards')
 
-    expect(response).to redirect_to(group_boards_path(group))
+      expect(response).to redirect_to(group_boards_path(group))
+    end
+
+    it 'redirects to the boards page with additional params' do
+      get('/groups/gitlabhq/boards/1?foo=bar')
+
+      expect(response).to redirect_to(group_board_path(group, 1, foo: 'bar'))
+    end
+  end
+
+  context 'when a group called boards exists', :nested_groups do
+    before do
+      create(:group, name: 'boards', parent: group)
+    end
+
+    it 'does not redirect to the main boards page' do
+      get('/groups/gitlabhq/boards')
+
+      expect(response).to have_gitlab_http_status(200)
+    end
+
+    it 'does not redirect to the boards page with additional params' do
+      get('/groups/gitlabhq/boards/issues')
+
+      expect(response).to have_gitlab_http_status(200)
+    end
+
+    it 'redirects to the boards page with additional params if there is no matching route on the subgroup' do
+      get('/groups/gitlabhq/boards/1?foo=bar')
+
+      expect(response).to redirect_to(group_board_path(group, 1, foo: 'bar'))
+    end
   end
 end