Make Rails/EnvironmentComparison cop detect comparisons in case statements

Closes rubocop#1395

Author: tejasbubane

lib/rubocop/cop/rails/environment_comparison.rb

@@ -22,11 +22,13 @@ class EnvironmentComparison < Base
 
         SYM_MSG = 'Do not compare `Rails.env` with a symbol, it will always evaluate to `false`.'
 
+        CASE_MSG = 'Favor environment check predicate methods over case comparison.'
+
         RESTRICT_ON_SEND = %i[== !=].freeze
 
         def_node_matcher :comparing_str_env_with_rails_env_on_lhs?, <<~PATTERN
           (send
-            (send (const {nil? cbase} :Rails) :env)
+            #rails_env_const?
             {:== :!=}
             $str
           )
@@ -36,13 +38,13 @@ class EnvironmentComparison < Base
           (send
             $str
             {:== :!=}
-            (send (const {nil? cbase} :Rails) :env)
+            #rails_env_const?
           )
         PATTERN
 
         def_node_matcher :comparing_sym_env_with_rails_env_on_lhs?, <<~PATTERN
           (send
-            (send (const {nil? cbase} :Rails) :env)
+            #rails_env_const?
             {:== :!=}
             $sym
           )
@@ -52,14 +54,18 @@ class EnvironmentComparison < Base
           (send
             $sym
             {:== :!=}
-            (send (const {nil? cbase} :Rails) :env)
+            #rails_env_const?
           )
         PATTERN
 
         def_node_matcher :content, <<~PATTERN
           ({str sym} $_)
         PATTERN
 
+        def_node_matcher :rails_env_const?, <<~PATTERN
+          (send (const {nil? cbase} :Rails) :env)
+        PATTERN
+
         def on_send(node)
           if (env_node = comparing_str_env_with_rails_env_on_lhs?(node) ||
                          comparing_str_env_with_rails_env_on_rhs?(node))
@@ -79,6 +85,13 @@ def on_send(node)
           end
         end
 
+        def on_case(case_node)
+          condition = case_node.condition
+          return unless rails_env_const?(condition)
+
+          add_offense(condition, message: CASE_MSG)
+        end
+
         private
 
         def autocorrect(corrector, node)

spec/rubocop/cop/rails/environment_comparison_spec.rb

@@ -101,10 +101,51 @@
     end
   end
 
+  context 'when comparing Rails.env using a case statement' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        case Rails.env
+             ^^^^^^^^^ Favor environment check predicate methods over case comparison.
+        when "production"
+          do_production_thing
+        when "staging"
+          do_staging_thing
+        else
+          do_other_thing
+        end
+      RUBY
+    end
+
+    context 'with pattern matching' do
+      it 'register an offense' do
+        expect_offense(<<~RUBY)
+          case Rails.env
+               ^^^^^^^^^ Favor environment check predicate methods over case comparison.
+          when "test" | "development"
+            do_test_thing
+          else
+            do_other_thing
+          end
+        RUBY
+      end
+    end
+  end
+
   it 'does not register an offense when using `#good_method`' do
     expect_no_offenses(<<~RUBY)
       Rails.env.production?
       Rails.env.test?
     RUBY
   end
+
+  it 'does not register an offense for other case statements' do
+    expect_no_offenses(<<~RUBY)
+      case some_method
+      when "test" | "development"
+        do_test_thing
+      else
+        do_other_thing
+      end
+    RUBY
+  end
 end