Hide empty merge request diffs when comparing versions

app/controllers/projects/merge_requests_controller.rb

@@ -82,12 +82,12 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
     @merge_request_diff =
       if params[:diff_id]
-        @merge_request.merge_request_diffs.find(params[:diff_id])
+        @merge_request.merge_request_diffs.viewable.find(params[:diff_id])
       else
         @merge_request.merge_request_diff
       end
 
-    @merge_request_diffs = @merge_request.merge_request_diffs.select_without_diff
+    @merge_request_diffs = @merge_request.merge_request_diffs.viewable.select_without_diff
     @comparable_diffs = @merge_request_diffs.select { |diff| diff.id < @merge_request_diff.id }
 
     if params[:start_sha].present?

app/models/merge_request_diff.rb

@@ -11,6 +11,9 @@ class MergeRequestDiff < ActiveRecord::Base
 
   belongs_to :merge_request
 
+  serialize :st_commits
+  serialize :st_diffs
+
   state_machine :state, initial: :empty do
     state :collected
     state :overflow
@@ -22,8 +25,7 @@ class MergeRequestDiff < ActiveRecord::Base
     state :overflow_diff_lines_limit
   end
 
-  serialize :st_commits
-  serialize :st_diffs
+  scope :viewable, -> { without_state(:empty) }
 
   # All diff information is collected from repository after object is created.
   # It allows you to override variables like head_commit_sha before getting diff.

changelogs/unreleased/hide-empty-merge-request-diffs.yml

+---
+title: Fix errors happening when source branch of merge request is removed and then restored
+merge_request: 7568
+author:

spec/features/merge_requests/merge_request_versions_spec.rb

@@ -3,11 +3,12 @@ require 'spec_helper'
 feature 'Merge Request versions', js: true, feature: true do
   let(:merge_request) { create(:merge_request, importing: true) }
   let(:project) { merge_request.source_project }
+  let!(:merge_request_diff1) { merge_request.merge_request_diffs.create(head_commit_sha: '6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9') }
+  let!(:merge_request_diff2) { merge_request.merge_request_diffs.create(head_commit_sha: nil) }
+  let!(:merge_request_diff3) { merge_request.merge_request_diffs.create(head_commit_sha: '5937ac0a7beb003549fc5fd26fc247adbce4a52e') }
 
   before do
     login_as :admin
-    merge_request.merge_request_diffs.create(head_commit_sha: '6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9')
-    merge_request.merge_request_diffs.create(head_commit_sha: '5937ac0a7beb003549fc5fd26fc247adbce4a52e')
     visit diffs_namespace_project_merge_request_path(project.namespace, project, merge_request)
   end
 
@@ -53,7 +54,7 @@ feature 'Merge Request versions', js: true, feature: true do
         project.namespace,
         project,
         merge_request.iid,
-        diff_id: 2,
+        diff_id: merge_request_diff3.id,
         start_sha: '6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9'
       )
     end