When viewing a commit, do not go to the blob for the file path

This avoids a slow Gitaly call. We already have the filename in memory,
so can use it directly here.

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

@@ -24,9 +24,9 @@
             %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
-                - if diff_file.blob&.name
+                - if diff_file.file_path
                   %strong.diff-changed-file-name
-                    = diff_file.blob.name
+                    = diff_file.file_path
                 - else
                   %strong.diff-changed-blank-file-name
                     = s_('Diffs|No file name available')

changelogs/unreleased/31118-do-not-use-blob-for-file-path.yml

+---
+title: Reduce Gitaly calls when viewing a commit
+merge_request: 17095
+author:
+type: performance

lib/gitlab/diff/file.rb

@@ -428,8 +428,8 @@ module Gitlab
 
       def viewer_class_from(classes)
         return unless diffable?
-        return if different_type? || external_storage_error?
         return unless new_file? || deleted_file? || content_changed?
+        return if different_type? || external_storage_error?
 
         verify_binary = !stored_externally?
 

spec/features/projects/commits/user_browses_commits_spec.rb

@@ -93,13 +93,13 @@ describe 'User browses commits' do
   context 'when the blob does not exist' do
     let(:commit) { create(:commit, project: project) }
 
-    it 'shows a blank label' do
+    it 'renders successfully' do
       allow_any_instance_of(Gitlab::Diff::File).to receive(:blob).and_return(nil)
       allow_any_instance_of(Gitlab::Diff::File).to receive(:binary?).and_return(true)
 
       visit(project_commit_path(project, commit))
 
-      expect(find('.diff-file-changes', visible: false)).to have_content('No file name available')
+      expect(find('.diff-file-changes', visible: false)).to have_content('files/ruby/popen.rb')
     end
   end