Return file name from repo in snippet endpoints

We need to return first the file name in the
repository instead of the data from the database.

app/models/snippet.rb

@@ -322,6 +322,12 @@ class Snippet < ApplicationRecord
     ::Feature.enabled?(:version_snippets, user) && repository_exists?
   end
 
+  def file_name_on_repo
+    return if repository.empty?
+
+    repository.ls_files(repository.root_ref).first
+  end
+
   class << self
     # Searches for snippets with a matching title, description or file name.
     #

changelogs/unreleased/fj-return-proper-file-name-snippet-entity.yml

+---
+title: Return file name from repo in snippet endpoints
+merge_request: 29785
+author:
+type: fixed

lib/api/entities/snippet.rb

@@ -3,7 +3,7 @@
 module API
   module Entities
     class Snippet < Grape::Entity
-      expose :id, :title, :file_name, :description, :visibility
+      expose :id, :title, :description, :visibility
       expose :author, using: Entities::UserBasic
       expose :updated_at, :created_at
       expose :project_id
@@ -14,6 +14,10 @@ module API
         Gitlab::UrlBuilder.build(snippet, raw: true)
       end
       expose :ssh_url_to_repo, :http_url_to_repo, if: ->(snippet) { snippet.versioned_enabled_for?(options[:current_user]) }
+      expose :file_name do |snippet|
+        (::Feature.enabled?(:version_snippets, options[:current_user]) && snippet.file_name_on_repo) ||
+          snippet.file_name
+      end
     end
   end
 end

spec/lib/api/entities/snippet_spec.rb

@@ -19,9 +19,30 @@ describe ::API::Entities::Snippet do
     it { expect(subject[:created_at]).to eq snippet.created_at }
     it { expect(subject[:project_id]).to eq snippet.project_id }
     it { expect(subject[:visibility]).to eq snippet.visibility }
-    it { expect(subject[:file_name]).to eq snippet.file_name }
     it { expect(subject).to include(:author) }
 
+    describe 'file_name' do
+      it 'returns attribute from repository' do
+        expect(subject[:file_name]).to eq snippet.blobs.first.path
+      end
+
+      context 'when feature flag :version_snippets is disabled' do
+        it 'returns attribute from db' do
+          stub_feature_flags(version_snippets: false)
+
+          expect(subject[:file_name]).to eq snippet.file_name
+        end
+      end
+
+      context 'when repository is empty' do
+        it 'returns attribute from db' do
+          allow(snippet.repository).to receive(:empty?).and_return(true)
+
+          expect(subject[:file_name]).to eq snippet.file_name
+        end
+      end
+    end
+
     describe 'ssh_url_to_repo' do
       it 'returns attribute' do
         expect(subject[:ssh_url_to_repo]).to eq snippet.ssh_url_to_repo

spec/requests/api/project_snippets_spec.rb

@@ -94,7 +94,7 @@ describe API::ProjectSnippets do
 
       expect(json_response['title']).to eq(snippet.title)
       expect(json_response['description']).to eq(snippet.description)
-      expect(json_response['file_name']).to eq(snippet.file_name)
+      expect(json_response['file_name']).to eq(snippet.file_name_on_repo)
       expect(json_response['ssh_url_to_repo']).to eq(snippet.ssh_url_to_repo)
       expect(json_response['http_url_to_repo']).to eq(snippet.http_url_to_repo)
     end

spec/requests/api/snippets_spec.rb

@@ -155,7 +155,7 @@ describe API::Snippets do
 
       expect(json_response['title']).to eq(private_snippet.title)
       expect(json_response['description']).to eq(private_snippet.description)
-      expect(json_response['file_name']).to eq(private_snippet.file_name)
+      expect(json_response['file_name']).to eq(private_snippet.file_name_on_repo)
       expect(json_response['visibility']).to eq(private_snippet.visibility)
       expect(json_response['ssh_url_to_repo']).to eq(private_snippet.ssh_url_to_repo)
       expect(json_response['http_url_to_repo']).to eq(private_snippet.http_url_to_repo)