Merge branch 'patch/fix-mergerequest-diff' into 'master'

Fix Raw / Rendered diff producing different results on merge requests

The raw diff endpoint (`merge_requests/####.diff`) produces a diff based on `target_branch` instead of the original branching point. Same is valid for `merge_requests/####.patch`.

Fixes #14680, #3017

See merge request !3450
Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG

@@ -5,6 +5,7 @@ v 8.6.3 (unreleased)
 v 8.6.3 (unreleased)
   - Destroy related todos when an Issue/MR is deleted. !3376
   - Fix error 500 when target is nil on todo list. !3376
+  - Fix raw/rendered diff producing different results on merge requests. !3450
 
 v 8.6.2
   - Fix dropdown alignment. !3298

app/controllers/projects/merge_requests_controller.rb

@@ -57,8 +57,8 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     respond_to do |format|
       format.html
       format.json { render json: @merge_request }
-      format.diff { render text: @merge_request.to_diff(current_user) }
-      format.patch { render text: @merge_request.to_patch(current_user) }
+      format.diff { render text: @merge_request.to_diff }
+      format.patch { render text: @merge_request.to_patch }
     end
   end
 

app/models/merge_request.rb

@@ -331,15 +331,15 @@ class MergeRequest < ActiveRecord::Base
   # Returns the raw diff for this merge request
   #
   # see "git diff"
-  def to_diff(current_user)
-    target_project.repository.diff_text(target_branch, source_sha)
+  def to_diff
+    target_project.repository.diff_text(diff_base_commit.sha, source_sha)
   end
 
   # Returns the commit as a series of email patches.
   #
   # see "git format-patch"
-  def to_patch(current_user)
-    target_project.repository.format_patch(target_branch, source_sha)
+  def to_patch
+    target_project.repository.format_patch(diff_base_commit.sha, source_sha)
   end
 
   def hook_attrs

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -63,7 +63,7 @@ describe Projects::MergeRequestsController do
             id: merge_request.iid,
             format: format)
 
-        expect(response.body).to eq((merge_request.send(:"to_#{format}",user)).to_s)
+        expect(response.body).to eq((merge_request.send(:"to_#{format}")).to_s)
       end
 
       it "should not escape Html" do