Now refactor all to work properly.

app/helpers/commits_helper.rb

@@ -23,13 +23,55 @@ module CommitsHelper
       end
   end
 
-  def side_diff_line(diff, index)
+  def parallel_diff_line(diff, index)
     Gitlab::DiffParser.new(diff.diff.lines.to_a, diff.new_path)
       .each do |full_line, type, line_code, line_new, line_old, raw_line, next_type, next_line|
         yield(full_line, type, line_code, line_new, line_old, raw_line, next_type, next_line)
       end
   end
 
+  def parallel_diff(diff, index)
+    lines = []
+    skip_next = false
+
+    # Building array of lines
+    #
+    # [left_type, left_line_number, left_line_content, right_line_type, right_line_number, right_line_content]
+    #
+    parallel_diff_line(diff, index) do |full_line, type, line_code, line_new, line_old, raw_line, next_type, next_line|
+      line = [type, line_old, full_line, next_type, line_new]
+      if type == 'match' || type.nil?
+        # line in the right panel is the same as in the left one
+        line = [type, line_old, full_line, type, line_new, full_line]
+        lines.push(line)
+      elsif type == 'old'
+        if next_type == 'new'
+          # Left side has text removed, right side has text added
+          line.push(next_line)
+          lines.push(line)
+          skip_next = true
+        elsif next_type == 'old' || next_type.nil?
+          # Left side has text removed, right side doesn't have any change
+          line.pop # remove the newline
+          line.push(nil) # no line number on the right panel
+          line.push(" ") # empty line on the right panel
+          lines.push(line)
+        end
+      elsif type == 'new'
+        if skip_next
+          # Change has been already included in previous line so no need to do it again
+          skip_next = false
+          next
+        else
+          # Change is only on the right side, left side has no change
+          line = [nil, nil, " ", type, line_new, full_line]
+          lines.push(line)
+        end
+      end
+    end
+    lines
+  end
+
   def each_diff_line_near(diff, index, expected_line_code)
     max_number_of_lines = 16
 
@@ -112,82 +154,6 @@ module CommitsHelper
     branches.sort.map { |branch| link_to(branch, project_tree_path(project, branch)) }.join(", ").html_safe
   end
 
-  def parallel_diff_lines(project, commit, diff, file)
-    old_file = project.repository.blob_at(commit.parent_id, diff.old_path) if commit.parent_id
-    deleted_lines = {}
-    added_lines = {}
-    each_diff_line(diff, 0) do |line, type, line_code, line_new, line_old|
-      if type == "old"
-        deleted_lines[line_old] = { line_code: line_code, type: type, line: line }
-      elsif type == "new"
-        added_lines[line_new]   = { line_code: line_code, type: type, line: line }
-      end
-    end
-    max_length = old_file ? [old_file.loc, file.loc].max : file.loc
-
-    offset1 = 0
-    offset2 = 0
-    old_lines = []
-    new_lines = []
-
-    max_length.times do |line_index|
-      line_index1 = line_index - offset1
-      line_index2 = line_index - offset2
-      deleted_line = deleted_lines[line_index1 + 1]
-      added_line = added_lines[line_index2 + 1]
-      old_line = old_file.lines[line_index1] if old_file
-      new_line = file.lines[line_index2]
-
-      if deleted_line && added_line
-      elsif deleted_line
-        new_line = nil
-        offset2 += 1
-      elsif added_line
-        old_line = nil
-        offset1 += 1
-      end
-
-      old_lines[line_index] = DiffLine.new
-      new_lines[line_index] = DiffLine.new
-
-      # old
-      if line_index == 0 && diff.new_file
-        old_lines[line_index].type = :file_created
-        old_lines[line_index].content = 'File was created'
-      elsif deleted_line
-        old_lines[line_index].type = :deleted
-        old_lines[line_index].content = old_line
-        old_lines[line_index].num = line_index1 + 1
-        old_lines[line_index].code = deleted_line[:line_code]
-      elsif old_line
-        old_lines[line_index].type = :no_change
-        old_lines[line_index].content = old_line
-        old_lines[line_index].num = line_index1 + 1
-      else
-        old_lines[line_index].type = :added
-      end
-
-      # new
-      if line_index == 0 && diff.deleted_file
-        new_lines[line_index].type = :file_deleted
-        new_lines[line_index].content = "File was deleted"
-      elsif added_line
-        new_lines[line_index].type = :added
-        new_lines[line_index].num = line_index2 + 1
-        new_lines[line_index].content = new_line
-        new_lines[line_index].code = added_line[:line_code]
-      elsif new_line
-        new_lines[line_index].type = :no_change
-        new_lines[line_index].num = line_index2 + 1
-        new_lines[line_index].content = new_line
-      else
-        new_lines[line_index].type = :deleted
-      end
-    end
-
-    return old_lines, new_lines
-  end
-
   def link_to_browse_code(project, commit)
     if current_controller?(:projects, :commits)
       if @repo.blob_at(commit.id, @path)

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

 / Side-by-side diff view
 %div.text-file
   %table
-    - side_diff_line(diff, index) do |line, type, line_code, line_new, line_old, raw_line, next_type, next_line|
-      %tr.line_holder.parallel{ id: line_code }
-        - if type == "match"
-          = render "projects/commits/diffs/match_line_parallel", {line: line,
-          line_old: line_old, line_new: line_new, bottom: false}
-        - else
-          - if diff.new_file
+    - parallel_diff(diff, index).each do |line|
+      - type_left = line[0]
+      - line_number_left = line[1]
+      - line_content_left = line[2]
+      - type_right = line[3]
+      - line_number_right = line[4]
+      - line_content_right = line[5]
+
+      %tr.line_holder.parallel
+        - if type_left == 'match'
+          = render "projects/commits/diffs/match_line_parallel", {line: line_content_left,
+          line_old: line_number_left, line_new: line_number_right, bottom: false}
+        - elsif type_left ==  'old'
+          %td.old_line{ class: "old" }
+            = link_to raw(line_number_left)
+            %td.line_content{class: "parallel noteable_line old"}= raw line_content_left
+          %td.new_line{class: "#{type_right == 'new' ? 'new' : nil}", data: {linenumber: line_number_right}}
+            = link_to raw(line_number_right)
+            %td.line_content.parallel{class: "noteable_line #{type_right == 'new' ? 'new' : nil}"}= raw line_content_right
+        - elsif type_left.nil?
           %td.old_line
-            %td.line_content.parallel= raw " "
-          - else
-            - next if type == 'new'
-            %td.old_line{ class: "#{type}" }
-              = link_to raw(line_old), "##{line_code}", id: line_code
-              - if type == 'old'
-                %td.line_content{class: "parallel noteable_line old #{line_code}", "line_code" => line_code}= raw line
-              - else
-                %td.line_content.parallel= raw line
-          - if diff.deleted_file
-            %td.new_line{ data: {linenumber: line_new}}
-            %td.line_content.parallel= raw " "
-          - else
-            - if type == 'old'
-              %td.new_line{class: "#{next_type == 'new' ? 'new' : nil}", data: {linenumber: line_new}}
-                - if next_type == 'new'
-                  - content = next_line
-                  = link_to raw(line_new) , "##{line_code}", id: line_code
-                  %td.line_content.parallel{class: "noteable_line new #{line_code}", "line_code" => line_code}= raw content
-                - else
-                  - content = " "
-                  %td.line_content.parallel{class: "noteable_line #{line_code}", "line_code" => line_code}= raw content
-            - else
-              %td.new_line{class: "#{type}", data: {linenumber: line_new}}
-                = link_to raw(line_new) , "##{line_code}", id: line_code
-                %td.line_content.parallel{class: "#{type}"}= raw line
+            = link_to raw(line_number_left)
+            %td.line_content{class: "parallel noteable_line"}= raw line_content_left
+          %td.new_line{class: "#{type_right == 'new' ? 'new' : nil}", data: {linenumber: line_number_right}}
+            = link_to raw(line_number_right)
+            %td.line_content.parallel{class: "noteable_line #{type_right == 'new' ? 'new' : nil}"}= raw line_content_right
 
 - if diff.diff.blank? && diff_file_mode_changed?(diff)
   .file-mode-changed