Set default query string when searching with filters

ee/changelogs/unreleased/258377_search_filter_defaults.yml

+---
+title: Set default query string when searching with filters
+merge_request: 49872
+author:
+type: added

ee/spec/models/concerns/elastic/repository_spec.rb

@@ -63,6 +63,24 @@ RSpec.describe Repository, :elastic do
 
     # Finds files/ruby/popen.rb
     expect(project.repository.elastic_search('* blob:7e3e39ebb9b2bf433b4ad17313770fbe4051649c')[:blobs][:total_count]).to eq(1)
+
+    # filename filter without search term
+    count = project.repository.ls_files('master').count { |path| path.split('/')[-1].include?('test') }
+    expect(project.repository.elastic_search('filename:test')[:blobs][:total_count]).to eq(count)
+    expect(project.repository.elastic_search('filename:test')[:blobs][:total_count]).to be > 0
+
+    # extension filter without search term
+    count = project.repository.ls_files('master').count { |path| path.split('/')[-1].split('.')[-1].include?('md') }
+    expect(project.repository.elastic_search('extension:md')[:blobs][:total_count]).to eq(count)
+    expect(project.repository.elastic_search('extension:md')[:blobs][:total_count]).to be > 0
+
+    # path filter without search term
+    count = project.repository.ls_files('master').count { |path| path.include?('ruby') }
+    expect(project.repository.elastic_search('path:ruby')[:blobs][:total_count]).to eq(count)
+    expect(project.repository.elastic_search('path:ruby')[:blobs][:total_count]).to be > 0
+
+    # blob filter without search term
+    expect(project.repository.elastic_search('blob:7e3e39ebb9b2bf433b4ad17313770fbe4051649c')[:blobs][:total_count]).to eq(1)
   end
 
   def search_and_check!(on, query, type:, per: 1000)

lib/gitlab/search/query.rb

@@ -51,6 +51,7 @@ module Gitlab
         end
 
         query = (@raw_query.split - fragments).join(' ')
+        query = '*' if query.empty?
 
         [query, filters]
       end