[Fixes rubocop#8478] Relax Lint/BinaryOperatorWithIdenticalOperands f…

…or mathematical operations

Simplified one of the `basic_literal?`, since we'd only raise an offense if they are
equal, in which case `basic_literal?` has the same result on both `lhs` and `rhs`...

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#8478](https://github.com/rubocop-hq/rubocop/issues/8478): Relax `Lint/BinaryOperatorWithIdenticalOperands` for mathematical operations. ([@marcandre][])
+
 ## 0.89.0 (2020-08-05)
 
 ### New features

lib/rubocop/cop/lint/binary_operator_with_identical_operands.rb

@@ -29,12 +29,13 @@ module Lint
       #
       class BinaryOperatorWithIdenticalOperands < Base
         MSG = 'Binary operator `%<op>s` has identical operands.'
+        MATH_OPERATORS = %i[+ - * / % ** << >> | ^].to_set.freeze
 
         def on_send(node)
           return unless node.binary_operation?
 
           lhs, operation, rhs = *node
-          return if node.arithmetic_operation? && lhs.basic_literal? && rhs.basic_literal?
+          return if MATH_OPERATORS.include?(node.method_name) && rhs.basic_literal?
 
           add_offense(node, message: format(MSG, op: operation)) if lhs == rhs
         end

spec/rubocop/cop/lint/binary_operator_with_identical_operands_spec.rb

@@ -28,6 +28,7 @@
   it 'does not register an offense when using arithmetic operator with numerics' do
     expect_no_offenses(<<~RUBY)
       x = 2 + 2
+      x = 1 << 1
     RUBY
   end
 end