Handle legacy `LambdaNode

spec/rubocop/cop/thread_safety/class_instance_variable_spec.rb

@@ -157,6 +157,23 @@ def some_method(params)
     RUBY
   end
 
+  # rubocop:disable RSpec/ExampleLength
+  it 'registers an offense for assigning an ivar in class_methods within lambda', :with_legacy_lambda_node do
+    expect_offense(<<~RUBY)
+      module Test
+        class_methods do
+          ->() {
+            def some_method(params)
+              @params = params
+              ^^^^^^^ #{msg}
+            end
+          }
+        end
+      end
+    RUBY
+  end
+  # rubocop:enable RSpec/ExampleLength
+
   it 'registers an offense for assigning an ivar in a class singleton method' do
     expect_offense(<<~RUBY)
       class Test

spec/spec_helper.rb

@@ -16,6 +16,7 @@
 
 $LOAD_PATH.unshift File.expand_path('../lib', __dir__)
 require 'rubocop-thread_safety'
+require 'rubocop-ast'
 
 require 'rubocop/rspec/support'
 require_relative 'shared_contexts'
@@ -40,6 +41,15 @@
     config.fail_fast = ENV.key? 'RSPEC_FAIL_FAST'
   end
 
+  config.around :each, :with_legacy_lambda_node do |example|
+    initial_value = RuboCop::AST::Builder.emit_lambda
+    RuboCop::AST::Builder.emit_lambda = true
+
+    example.call
+  ensure
+    RuboCop::AST::Builder.emit_lambda = initial_value
+  end
+
   config.filter_run_excluding unsupported_on: :prism if ENV['PARSER_ENGINE'] == 'parser_prism'
 
   config.disable_monkey_patching!