Fix 500 when visiting a commit where blobs do not exist (nil blobs)

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/41491

app/assets/stylesheets/pages/diff.scss

@@ -651,12 +651,18 @@
     min-width: 0;
   }
 
-  .diff-changed-file-name {
+  .diff-changed-file-name,
+  .diff-changed-blank-file-name {
     overflow: hidden;
     text-overflow: ellipsis;
     white-space: nowrap;
   }
 
+  .diff-changed-blank-file-name {
+    color: $gl-text-color-tertiary;
+    font-style: italic;
+  }
+
   .diff-changed-file-path {
     color: $gl-text-color-tertiary;
   }

app/views/projects/diffs/_file.html.haml

@@ -11,7 +11,7 @@
     - unless diff_file.submodule?
       - blob = diff_file.blob
       .file-actions.hidden-xs
-        - if blob.readable_text?
+        - if blob&.readable_text?
           = link_to '#', class: 'js-toggle-diff-comments btn active has-tooltip', title: "Toggle comments for this file", disabled: @diff_notes_disabled do
             = icon('comment')
           \

app/views/projects/diffs/_stats.html.haml

@@ -24,7 +24,12 @@
             %a.diff-changed-file{ href: "##{hexdigest(diff_file.file_path)}", title: diff_file.new_path }
               = sprite_icon(diff_file_changed_icon(diff_file), size: 16, css_class: "#{diff_file_changed_icon_color(diff_file)} diff-file-changed-icon append-right-8")
               %span.diff-changed-file-content.append-right-8
-                %strong.diff-changed-file-name= diff_file.blob.name
+                - if diff_file.blob&.name
+                  %strong.diff-changed-file-name
+                    = diff_file.blob.name
+                - else
+                  %strong.diff-changed-blank-file-name
+                    = s_('Diffs|No file name available')
                 %span.diff-changed-file-path.prepend-top-5= diff_file_path_text(diff_file)
               %span.diff-changed-stats
                 %span.cgreen<

changelogs/unreleased/41491-fix-nil-blob-name-error.yml

+---
+title: Fix 500 error when visiting a commit where the blobs do not exist
+merge_request:
+author:
+type: fixed

spec/features/projects/commits/user_browses_commits_spec.rb

 require 'spec_helper'
 
-describe 'User broweses commits' do
+describe 'User browses commits' do
   let(:user) { create(:user) }
   let(:project) { create(:project, :repository, namespace: user.namespace) }
 
@@ -31,6 +31,19 @@ describe 'User broweses commits' do
       check_author_link(RepoHelpers.sample_commit.author_email, user)
     end
   end
+
+  context 'when the blob does not exist' do
+    let(:commit) { create(:commit, project: project) }
+
+    it 'shows a blank label' do
+      allow_any_instance_of(Gitlab::Diff::File).to receive(:blob).and_return(nil)
+      allow_any_instance_of(Gitlab::Diff::File).to receive(:raw_binary?).and_return(true)
+
+      visit(project_commit_path(project, commit))
+
+      expect(find('.diff-file-changes', visible: false)).to have_content('No file name available')
+    end
+  end
 end
 
 private