[Fix #12865] require 'bundler' if possible and rescue Bundler::GemfileNotFound

changelog/fix_rails_cops_outside_bundler_exec.md

@@ -0,0 +1 @@
+* [#12865](https://github.com/rubocop/rubocop/issues/12865): Fix Rails Cops, which weren't reporting any violations unless running with `bundle exec`. ([@amomchilov][])

lib/rubocop/lockfile.rb

@@ -1,13 +1,25 @@
 # frozen_string_literal: true
 
+begin
+  # We might not be running with `bundle exec`, so we need to pull in Bundler ourselves,
+  # in order to use `Bundler::LockfileParser`.
+  require 'bundler'
+rescue LoadError
+  nil
+end
+
 module RuboCop
   # Encapsulation of a lockfile for use when checking for gems.
   # Does not actually resolve gems, just parses the lockfile.
   # @api private
   class Lockfile
     # @param [String, Pathname, nil] lockfile_path
     def initialize(lockfile_path = nil)
-      lockfile_path ||= Bundler.default_lockfile if bundler_lock_parser_defined?
+      lockfile_path ||= begin
+        ::Bundler.default_lockfile if bundler_lock_parser_defined?
+      rescue ::Bundler::GemfileNotFound
+        nil # We might not be a folder with a Gemfile, but that's okay.
+      end
 
       @lockfile_path = lockfile_path
     end