[Fix rubocop#7569] Make Style/YodaCondition accept __FILE__ == $0

Fixes rubocop#7569.

This PR makes `Style/YodaCondition` cop accept `__FILE__ == $0`

I think that both operands `__FILE__ == $0` can be assumed to be
read-only, as mentioned in rubocop#7569. If users try to assign `__FILE__`,
an error will occur. Also, it is not usually assigned to `$0` by users.

Therefore, this PR will make `Style/YodaCondition` cop accept both
`__FILE__` and `$0` on the left side.

Also, this PR will change only an idiom `__FILE__ == $0`.

CHANGELOG.md

@@ -10,6 +10,7 @@
 
 * [#7193](https://github.com/rubocop-hq/rubocop/issues/7193): Prevent `Style/PercentLiteralDelimiters` from changing `%i` literals that contain escaped delimiters. ([@buehmann][])
 * [#7590](https://github.com/rubocop-hq/rubocop/issues/7590): Fix an error for `Layout/SpaceBeforeBlockBraces` when using with `EnforcedStyle: line_count_based` of `Style/BlockDelimiters` cop. ([@koic][])
+* [#7569](https://github.com/rubocop-hq/rubocop/issues/7569): Make `Style/YodaCondition` accept `__FILE__ == $0`. ([@koic][])
 
 ## 0.78.0 (2019-12-18)
 

lib/rubocop/cop/style/yoda_condition.rb

@@ -67,9 +67,16 @@ class YodaCondition < Cop
 
         NONCOMMUTATIVE_OPERATORS = %i[===].freeze
 
+        PROGRAM_NAMES = %i[$0 $PROGRAM_NAME].freeze
+
+        def_node_matcher :file_constant_equal_program_name?, <<~PATTERN
+          (send #source_file_path_constant? {:== :!=} (gvar #program_name?))
+        PATTERN
+
         def on_send(node)
           return unless yoda_compatible_condition?(node)
-          return if equality_only? && non_equality_operator?(node)
+          return if equality_only? && non_equality_operator?(node) ||
+                    file_constant_equal_program_name?(node)
 
           valid_yoda?(node) || add_offense(node)
         end
@@ -135,6 +142,14 @@ def non_equality_operator?(node)
         def noncommutative_operator?(node)
           NONCOMMUTATIVE_OPERATORS.include?(node.method_name)
         end
+
+        def source_file_path_constant?(node)
+          node.source == '__FILE__'
+        end
+
+        def program_name?(name)
+          PROGRAM_NAMES.include?(name)
+        end
       end
     end
   end

spec/rubocop/cop/style/yoda_condition_spec.rb

@@ -55,6 +55,10 @@
     it_behaves_like 'accepts', 'not true'
     it_behaves_like 'accepts', '0 <=> val'
     it_behaves_like 'accepts', '"foo" === bar'
+    it_behaves_like 'accepts', '__FILE__ == $0'
+    it_behaves_like 'accepts', '__FILE__ != $0'
+    it_behaves_like 'accepts', '__FILE__ == $PROGRAM_NAME'
+    it_behaves_like 'accepts', '__FILE__ != $PROGRAM_NAME'
 
     it_behaves_like 'offense', '"foo" == bar'
     it_behaves_like 'offense', 'nil == bar'