Compare merge request version against other version on changes page

app/controllers/projects/merge_requests_controller.rb

@@ -98,7 +98,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
           @diff_notes_disabled = true
         end
 
-        @diffs = @merge_request_diff.diffs(diff_options)
+        if params[:start_sha].present?
+          compare_diff_version
+        else
+          @diffs = @merge_request_diff.diffs(diff_options)
+        end
 
         render json: { html: view_to_html_string("projects/merge_requests/show/_diffs") }
       end
@@ -529,4 +533,15 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     params[:merge_request] ||= ActionController::Parameters.new(source_project: @project)
     @merge_request = MergeRequests::BuildService.new(project, current_user, merge_request_params).execute
   end
+
+  def compare_diff_version
+    @compare = CompareService.new.execute(@project, @merge_request_diff.head_commit_sha, @project, params[:start_sha])
+
+    if @compare
+      @commits = @compare.commits
+      @commit = @compare.commit
+      @diffs = @compare.diffs(diff_options)
+      @diff_notes_disabled = true
+    end
+  end
 end

app/helpers/merge_requests_helper.rb

@@ -101,7 +101,9 @@ module MergeRequestsHelper
     return 'hidden' if merge_request.closed? == closed || (merge_request.merged? == closed && !merge_request.closed?) || merge_request.closed_without_fork?
   end
 
-  def compare_versions_path(project, version, base_version)
-    namespace_project_compare_path(project.namespace, project, base_version.head_commit_sha, version.head_commit_sha)
+  def mr_version_path(project, merge_request, merge_request_diff, start_sha = nil)
+    diffs_namespace_project_merge_request_path(
+      project.namespace, project, merge_request,
+      diff_id: merge_request_diff.id, start_sha: start_sha)
   end
 end

app/views/projects/merge_requests/show/_versions.html.haml

@@ -26,28 +26,32 @@
       Compared with:
       %span.dropdown.inline
         %a.btn-link.dropdown-toggle{ data: {toggle: :dropdown} }
-          %strong.monospace base
+          %strong.monospace<
+            - if params[:start_sha].present?
+              #{params[:start_sha][0...8]}
+            - else
+              #{"base"}
           %span.caret
         %ul.dropdown-menu.dropdown-menu-selectable
           - merge_request_diffs.each do |merge_request_diff|
             - next if merge_request_diff.id >= @merge_request_diff.id
             %li
-              = link_to compare_versions_path(@project, @merge_request_diff, merge_request_diff), class: ('is-active' if merge_request_diff == @base_version), target: '_blank' do
+              = link_to mr_version_path(@project, @merge_request, @merge_request_diff, merge_request_diff.head_commit_sha), class: ('is-active' if merge_request_diff.head_commit_sha == params[:start_sha]) do
                 %strong.monospace
                   #{merge_request_diff.head_commit.short_id}
                 %br
                 %small
                   = time_ago_with_tooltip(merge_request_diff.created_at)
           %li
-            = link_to '#', class: 'is-active' do
+            = link_to mr_version_path(@project, @merge_request, @merge_request_diff), class: ('is-active' unless params[:start_sha].present?) do
               %strong.monospace
                 base
 
-    - unless @merge_request_diff.latest?
-      %span.prepend-left-default
-        = icon('info-circle')
-        This version is not the latest one. Comments are disabled
 
-    .pull-right
-      %span.monospace
-        #{@merge_request_diff.base_commit.short_id}..#{@merge_request_diff.head_commit.short_id}
+    - unless @merge_request_diff.latest? && params[:start_sha].blank?
+      .pull-right
+        = icon('info-circle')
+        - if params[:start_sha].present?
+          Comments are disabled when compare with version different from base
+        - else
+          This version is not the latest one. Comments are disabled