Fix an error for Rails/Env

changelog/fix_an_error_for_rails_env.md

@@ -0,0 +1 @@
+* [#1556](https://github.com/rubocop/rubocop-rails/pull/1556): Fix an error for `Rails/Env` when assigning `Rails.env`. ([@koic][])

lib/rubocop/cop/rails/env.rb

@@ -45,7 +45,7 @@ def on_send(node)
           return unless node.receiver&.const_name == 'Rails'
 
           parent = node.parent
-          return unless parent&.predicate_method?
+          return unless parent.respond_to?(:predicate_method?) && parent.predicate_method?
 
           return if ALLOWED_LIST.include?(parent.method_name)
 

spec/rubocop/cop/rails/env_spec.rb

@@ -22,6 +22,12 @@
     RUBY
   end
 
+  it 'does not register an offense when assigning `Rails.env`' do
+    expect_no_offenses(<<~RUBY)
+      rails_env = Rails.env
+    RUBY
+  end
+
   it 'does not register an offense for valid Rails.env methods' do
     expect_no_offenses(<<~RUBY)
       Rails.env.capitalize