Refactor code for merge request version compare feature

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -90,18 +90,21 @@ class Projects::MergeRequestsController < Projects::ApplicationController
         @merge_request.merge_request_diff
       end
 
+    @merge_request_diffs = @merge_request.merge_request_diffs.select_without_diff
+    @comparable_diffs = @merge_request_diffs.select { |diff| diff.id < @merge_request_diff.id }
+
+    if params[:start_sha].present?
+      @start_sha = params[:start_sha]
+      validate_start_sha
+    end
+
     respond_to do |format|
       format.html { define_discussion_vars }
       format.json do
-        unless @merge_request_diff.latest?
-          # Disable comments if browsing older version of the diff
-          @diff_notes_disabled = true
-        end
-
-        if params[:start_sha].present?
-          compare_diff_version
+        if @start_sha
+          compared_diff_version
         else
-          @diffs = @merge_request_diff.diffs(diff_options)
+          original_diff_version
         end
 
         render json: { html: view_to_html_string("projects/merge_requests/show/_diffs") }
@@ -534,14 +537,27 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @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])
+  def compared_diff_version
+    compare = CompareService.new.execute(@project, @merge_request_diff.head_commit_sha, @project, @start_sha)
 
-    if @compare
-      @commits = @compare.commits
-      @commit = @compare.commit
-      @diffs = @compare.diffs(diff_options)
+    if compare
+      @diffs = compare.diffs(diff_options)
       @diff_notes_disabled = true
     end
   end
+
+  def original_diff_version
+    unless @merge_request_diff.latest?
+      # Disable comments if browsing older version of the diff
+      @diff_notes_disabled = true
+    end
+
+    @diffs = @merge_request_diff.diffs(diff_options)
+  end
+
+  def validate_start_sha
+    unless @comparable_diffs.map(&:head_commit_sha).include?(@start_sha)
+      render_404
+    end
+  end
 end

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

-- merge_request_diffs = @merge_request.merge_request_diffs.select_without_diff
-- compareable_diffs = merge_request_diffs.select { |diff| diff.id < @merge_request_diff.id }
-
-- if merge_request_diffs.size > 1
+- if @merge_request_diffs.size > 1
   .mr-version-controls
     Version
     %span.dropdown.inline.mr-version-dropdown
       %a.btn-link.dropdown-toggle{ data: {toggle: :dropdown} }
         %strong.monospace<
           - if @merge_request_diff.latest?
-            Latest: #{short_sha(@merge_request_diff.head_commit_sha)}
-          - else
+            Latest:&nbsp;
           #{short_sha(@merge_request_diff.head_commit_sha)}
         %span.caret
       %ul.dropdown-menu.dropdown-menu-selectable
-        - merge_request_diffs.each_with_index do |merge_request_diff, i|
+        - @merge_request_diffs.each_with_index do |merge_request_diff, i|
           %li
-            = link_to diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request, diff_id: merge_request_diff.id), class: ('is-active' if merge_request_diff == @merge_request_diff) do
+            = link_to mr_version_path(@project, @merge_request, merge_request_diff), class: ('is-active' if merge_request_diff == @merge_request_diff) do
               %strong.monospace
                 - if i.zero?
                   Latest:
                 - else
-                  #{merge_request_diffs.size - i}.
-                #{merge_request_diff.head_commit.short_id}
+                  #{@merge_request_diffs.size - i}.
+                #{short_sha(merge_request_diff.head_commit_sha)}
               %br
               %small
                 #{number_with_delimiter(merge_request_diff.commits.count)} #{'commit'.pluralize(merge_request_diff.commits.count)},
                 = time_ago_with_tooltip(merge_request_diff.created_at)
 
+    - if @merge_request_diff.base_commit_sha
       %span.compare-dots ...
 
       Compared with
       %span.dropdown.inline.mr-version-compare-dropdown
         %a.btn-link.dropdown-toggle{ data: {toggle: :dropdown} }
           %strong.monospace<
-          - if params[:start_sha].present?
-            #{short_sha(params[:start_sha])}
+            - if @start_sha
+              #{short_sha(@start_sha)}
             - else
               Base: #{short_sha(@merge_request_diff.base_commit_sha)}
           %span.caret
         %ul.dropdown-menu.dropdown-menu-selectable
-        - compareable_diffs.each_with_index do |merge_request_diff, i|
+          - @comparable_diffs.each_with_index do |merge_request_diff, i|
             %li
-            = 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
+              = 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 == @start_sha) do
                 %strong.monospace
-                #{compareable_diffs.size - i}. #{short_sha(merge_request_diff.head_commit_sha)}
+                  #{@comparable_diffs.size - i}. #{short_sha(merge_request_diff.head_commit_sha)}
                 %br
                 %small
                   = time_ago_with_tooltip(merge_request_diff.created_at)
           %li
-          = link_to mr_version_path(@project, @merge_request, @merge_request_diff), class: ('is-active' unless params[:start_sha].present?) do
+            = link_to mr_version_path(@project, @merge_request, @merge_request_diff), class: ('is-active' unless @start_sha) do
               %strong.monospace
                 Base: #{short_sha(@merge_request_diff.base_commit_sha)}
 
-    - unless @merge_request_diff.latest? && params[:start_sha].blank?
+    - unless @merge_request_diff.latest? && !@start_sha
       .prepend-top-10
         = icon('info-circle')
         Comments are disabled while viewing outdated merge versions or comparing to versions other than base.