Link Commits tab to current branch from Compare page.

app/controllers/projects/compare_controller.rb

@@ -6,11 +6,12 @@ class Projects::CompareController < Projects::ApplicationController
   before_action :authorize_download_code!
   def index
+    @ref = Addressable::URI.unescape(params[:to])
   end
   def show
     base_ref = Addressable::URI.unescape(params[:from])
-    head_ref = Addressable::URI.unescape(params[:to])
+    @ref = head_ref = Addressable::URI.unescape(params[:to])
     compare_result = CompareService.new.execute(
       current_user,

app/views/projects/commits/_head.html.haml

 %ul.nav.nav-tabs
   = nav_link(controller: [:commit, :commits]) do
-    = link_to namespace_project_commits_path(@project.namespace, @project, @repository.root_ref) do
+    = link_to namespace_project_commits_path(@project.namespace, @project, @ref || @repository.root_ref) do
       Commits
       %span.badge= number_with_precision(@repository.commit_count, precision: 0, delimiter: ',')
   = nav_link(controller: :compare) do