Always fetch MR latest version when creating suggestions

This is an issue that can only be seen through EE. Further
details can be seen on
https://gitlab.com/gitlab-org/gitlab-ee/issues/9876. In general
we should always use the latest diff version of a file in order
to both create and apply suggestions.

4 files changed, 25 insertions, 11 deletions

diff --git a/app/models/diff_note.rb b/app/models/diff_note.rb
index 279603496b0..bd9e146a40f 100644
--- a/app/models/diff_note.rb
+++ b/app/models/diff_note.rb
@@ -41,6 +41,15 @@ class DiffNote < Note
     create_note_diff_file(creation_params)
   end
 
+  # Returns the diff file from `position`
+  def latest_diff_file
+    strong_memoize(:latest_diff_file) do
+      repository = project.repository
+      position.diff_file(repository)
+    end
+  end
+
+  # Returns the diff file from `original_position`
   def diff_file
     strong_memoize(:diff_file) do
       enqueue_diff_file_creation_job if should_create_diff_file?
diff --git a/app/models/suggestion.rb b/app/models/suggestion.rb
index 7eee4fbbe5f..09034646bff 100644
--- a/app/models/suggestion.rb
+++ b/app/models/suggestion.rb
@@ -19,11 +19,6 @@ class Suggestion < ApplicationRecord
     position.file_path
   end
 
-  def diff_file
-    repository = project.repository
-    position.diff_file(repository)
-  end
-
   # For now, suggestions only serve as a way to send patches that
   # will change a single line (being able to apply multiple in the same place),
   # which explains `from_line` and `to_line` being the same line.
diff --git a/app/services/suggestions/apply_service.rb b/app/services/suggestions/apply_service.rb
index 1f720fc835f..f778c5aa5f5 100644
--- a/app/services/suggestions/apply_service.rb
+++ b/app/services/suggestions/apply_service.rb
@@ -15,7 +15,13 @@ module Suggestions
         return error('The file has been changed')
       end
 
-      params = file_update_params(suggestion)
+      diff_file = suggestion.note.latest_diff_file
+
+      unless diff_file
+        return error('The file was not found')
+      end
+
+      params = file_update_params(suggestion, diff_file)
       result = ::Files::UpdateService.new(suggestion.project, @current_user, params).execute
 
       if result[:status] == :success
@@ -38,8 +44,8 @@ module Suggestions
       suggestion.position.head_sha == suggestion.noteable.source_branch_sha
     end
 
-    def file_update_params(suggestion)
-      blob = suggestion.diff_file.new_blob
+    def file_update_params(suggestion, diff_file)
+      blob = diff_file.new_blob
       file_path = suggestion.file_path
       branch_name = suggestion.branch
       file_content = new_file_content(suggestion, blob)
diff --git a/app/services/suggestions/create_service.rb b/app/services/suggestions/create_service.rb
index 77e958cbe0c..c7ac2452c53 100644
--- a/app/services/suggestions/create_service.rb
+++ b/app/services/suggestions/create_service.rb
@@ -9,6 +9,10 @@ module Suggestions
     def execute
       return unless @note.supports_suggestion?
 
+      diff_file = @note.latest_diff_file
+
+      return unless diff_file
+
       suggestions = Banzai::SuggestionsParser.parse(@note.note)
 
       # For single line suggestion we're only looking forward to
@@ -20,7 +24,7 @@ module Suggestions
 
       rows =
         suggestions.map.with_index do |suggestion, index|
-          from_content = changing_lines(comment_line, comment_line)
+          from_content = changing_lines(diff_file, comment_line, comment_line)
 
           # The parsed suggestion doesn't have information about the correct
           # ending characters (we may have a line break, or not), so we take
@@ -44,8 +48,8 @@ module Suggestions
 
     private
 
-    def changing_lines(from_line, to_line)
-      @note.diff_file.new_blob_lines_between(from_line, to_line).join
+    def changing_lines(diff_file, from_line, to_line)
+      diff_file.new_blob_lines_between(from_line, to_line).join
     end
 
     def line_break_chars(line)