Merge branch 'bvl-fix-view-mr-deleted-repo' into 'master'

Return unloaded commit if  it couldn't be enriched

See merge request gitlab-org/gitlab!17894

app/models/commit_collection.rb

@@ -72,8 +72,15 @@ class CommitCollection
     end.compact]
 
     # Replace the commits, keeping the same order
-    @commits = @commits.map do |c|
-      replacements.fetch(c.id, c)
+    @commits = @commits.map do |original_commit|
+      # Return the original instance: if it didn't need to be batchloaded, it was
+      # already enriched.
+      batch_loaded_commit = replacements.fetch(original_commit.id, original_commit)
+
+      # If batch loading the commit failed, fall back to the original commit.
+      # We need to explicitly check `.nil?` since otherwise a `BatchLoader` instance
+      # that looks like `nil` is returned.
+      batch_loaded_commit.nil? ? original_commit : batch_loaded_commit
     end
 
     self

changelogs/unreleased/bvl-fix-view-mr-deleted-repo.yml

+---
+title: Fix viewing merge reqeust from a fork that's being deleted
+merge_request: 17894
+author:
+type: fixed

spec/features/merge_request/user_views_merge_request_from_deleted_fork_spec.rb

+# frozen_string_literal: true
+require 'spec_helper'
+
+# This is a feature spec because the problems arrise when rendering the view for
+# an actual project for which the repository is removed but the cached not
+# updated.
+# This can occur when the fork a merge request is created from is in the process
+# of being destroyed.
+describe 'User views merged merge request from deleted fork' do
+  include ProjectForksHelper
+
+  let(:project) { create(:project, :repository) }
+  let(:source_project) { fork_project(project, nil, repository: true) }
+  let(:user) { project.owner }
+  let!(:merge_request) { create(:merge_request, :merged, source_project: source_project, target_project: project) }
+
+  before do
+    sign_in user
+
+    fork_owner = source_project.namespace.owners.first
+    # Place the source_project in the weird in between state
+    source_project.update_attribute(:pending_delete, true)
+    Projects::DestroyService.new(source_project, fork_owner, {}).__send__(:trash_repositories!)
+  end
+
+  it 'correctly shows the merge request' do
+    visit(merge_request_path(merge_request))
+
+    expect(page).to have_content(merge_request.title)
+  end
+end

spec/models/commit_collection_spec.rb

@@ -149,6 +149,17 @@ describe CommitCollection do
 
         collection.enrich!
       end
+
+      it 'returns the original commit if the commit could not be lazy loaded' do
+        collection = described_class.new(project, [hash_commit])
+        unexisting_lazy_commit = Commit.lazy(project, Gitlab::Git::BLANK_SHA)
+
+        expect(Commit).to receive(:lazy).with(project, hash_commit.id).and_return(unexisting_lazy_commit)
+
+        collection.enrich!
+
+        expect(collection.commits).to contain_exactly(hash_commit)
+      end
     end
   end