Use the new path to the partial, move the diff related methods to the new helper.

app/helpers/commits_helper.rb

@@ -31,14 +31,6 @@ module CommitsHelper
     escape_javascript(render "projects/commits/#{template}", commit: commit, project: project) unless commit.nil?
   end
 
-  def diff_line_content(line)
-    if line.blank?
-      "  "
-    else
-      line
-    end
-  end
-
   # Breadcrumb links for a Project and, if applicable, a tree path
   def commits_breadcrumbs
     return unless @project && @ref
@@ -121,10 +113,6 @@ module CommitsHelper
     end
   end
 
-  def unfold_bottom_class(bottom)
-    (bottom) ? 'js-unfold-bottom' : ''
-  end
-
   def view_file_btn(commit_sha, diff, project)
     link_to project_blob_path(project, tree_join(commit_sha, diff.new_path)),
             class: 'btn btn-small view-file js-view-file' do

app/helpers/diff_helper.rb

@@ -86,4 +86,15 @@ module DiffHelper
     lines
   end
 
+  def unfold_bottom_class(bottom)
+    (bottom) ? 'js-unfold-bottom' : ''
+  end
+
+  def diff_line_content(line)
+    if line.blank?
+      "  "
+    else
+      line
+    end
+  end
 end

app/views/projects/blob/diff.html.haml

 - if @lines.present?
   - if @form.unfold? && @form.since != 1 && !@form.bottom?
     %tr.line_holder{ id: @form.since }
-      = render "projects/commits/diffs/match_line", {line: @match_line,
+      = render "projects/diffs/match_line", {line: @match_line,
         line_old: @form.since, line_new: @form.since, bottom: false}
 
   - @lines.each_with_index do |line, index|
@@ -15,5 +15,5 @@
 
   - if @form.unfold? && @form.bottom? && @form.to < @blob.loc
     %tr.line_holder{ id: @form.to }
-      = render "projects/commits/diffs/match_line", {line: @match_line,
+      = render "projects/diffs/match_line", {line: @match_line,
         line_old: @form.to, line_new: @form.to, bottom: true}