Handle case where conflicts aren't on disk yet

app/models/merge_request.rb

@@ -778,7 +778,7 @@ class MergeRequest < ActiveRecord::Base
 
     begin
       @conflicts_can_be_resolved_in_ui = conflicts.files.each(&:lines)
-    rescue Gitlab::Conflict::Parser::ParserError, Gitlab::Conflict::FileCollection::ConflictSideMissing
+    rescue Rugged::OdbError, Gitlab::Conflict::Parser::ParserError, Gitlab::Conflict::FileCollection::ConflictSideMissing
       @conflicts_can_be_resolved_in_ui = false
     end
   end

lib/gitlab/conflict/file.rb

@@ -181,6 +181,17 @@ module Gitlab
           sections: sections
         }
       end
+
+      # Don't try to print merge_request or repository.
+      def inspect
+        instance_variables = [:merge_file_result, :their_path, :our_path, :our_mode].map do |instance_variable|
+          value = instance_variable_get("@#{instance_variable}")
+
+          "#{instance_variable}=\"#{value}\""
+        end
+
+        "#<#{self.class} #{instance_variables.join(' ')}>"
+      end
     end
   end
 end

spec/models/merge_request_spec.rb

@@ -890,6 +890,13 @@ describe MergeRequest, models: true do
       expect(merge_request.conflicts_can_be_resolved_in_ui?).to be_falsey
     end
 
+    it 'returns a falsey value when the MR has a missing ref after a force push' do
+      merge_request = create_merge_request('conflict-resolvable')
+      allow(merge_request.conflicts).to receive(:merge_index).and_raise(Rugged::OdbError)
+
+      expect(merge_request.conflicts_can_be_resolved_in_ui?).to be_falsey
+    end
+
     it 'returns a falsey value when the MR does not support new diff notes' do
       merge_request = create_merge_request('conflict-resolvable')
       merge_request.merge_request_diff.update_attributes(start_commit_sha: nil)