Fix conflict resolution from corrupted upstream

I don't know why this happens exactly, but given an upstream and fork repository
from a customer, both of which required GC, resolving conflicts would corrupt
the fork so badly that it couldn't be cloned.

This isn't a perfect fix for that case, because the MR may still need to be
merged manually, but it does ensure that the repository is at least usable.

My best guess is that when we generate the index for the conflict
resolution (which we previously did in the target project), we obtain a
reference to an OID that doesn't exist in the source, even though we already
fetch the refs from the target into the source.

Explicitly setting the source project as the place to get the merge index from
seems to prevent repository corruption in this way.

1 files changed, 11 insertions, 7 deletions

diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 207fbad7856..b99ccd453b8 100755
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -155,8 +155,8 @@ class Projects::MergeRequestsController < Projects::ApplicationController
       format.html { define_discussion_vars }
 
       format.json do
-        if @merge_request.conflicts_can_be_resolved_in_ui?
-          render json: @merge_request.conflicts
+        if @conflicts_list.can_be_resolved_in_ui?
+          render json: @conflicts_list
         elsif @merge_request.can_be_merged?
           render json: {
             message: 'The merge conflicts for this merge request have already been resolved. Please return to the merge request.',
@@ -173,9 +173,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def conflict_for_path
-    return render_404 unless @merge_request.conflicts_can_be_resolved_in_ui?
+    return render_404 unless @conflicts_list.can_be_resolved_in_ui?
 
-    file = @merge_request.conflicts.file_for_path(params[:old_path], params[:new_path])
+    file = @conflicts_list.file_for_path(params[:old_path], params[:new_path])
 
     return render_404 unless file
 
@@ -183,7 +183,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def resolve_conflicts
-    return render_404 unless @merge_request.conflicts_can_be_resolved_in_ui?
+    return render_404 unless @conflicts_list.can_be_resolved_in_ui?
 
     if @merge_request.can_be_merged?
       render status: :bad_request, json: { message: 'The merge conflicts for this merge request have already been resolved.' }
@@ -191,7 +191,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     end
 
     begin
-      MergeRequests::ResolveService.new(@merge_request.source_project, current_user, params).execute(@merge_request)
+      MergeRequests::Conflicts::ResolveService.
+        new(merge_request).
+        execute(current_user, params)
 
       flash[:notice] = 'All merge conflicts were resolved. The merge request can now be merged.'
 
@@ -459,7 +461,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def authorize_can_resolve_conflicts!
-    return render_404 unless @merge_request.conflicts_can_be_resolved_by?(current_user)
+    @conflicts_list = MergeRequests::Conflicts::ListService.new(@merge_request)
+
+    return render_404 unless @conflicts_list.can_be_resolved_by?(current_user)
   end
 
   def module_enabled