Lint/BinaryOperatorWithIdenticalOperands warning for simple math

[ShockwaveNN]

Steps to reproduce the problem

1. Create test.rb file with

x = 1
y = x * x * 2
puts y

2. Runing rubocop on it result:

Offenses:

1.rb:2:5: W: Lint/BinaryOperatorWithIdenticalOperands: Binary operator * has identical operands.
y = x * x * 2

I'm thinking this case is out of scope of Lint/BinaryOperatorWithIdenticalOperands, just a simple math calculation

This code can be fixed by

y = x ^ 2 * 2

But I don't think original code is bad

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler. Here's an example:

$ [bundle exec] rubocop -V
0.89.0 (using Parser 2.7.1.4, rubocop-ast 0.3.0, running on ruby 2.7.1 x86_64-linux)

[bbatsov]

@marcandre had a partial fix for this, but I was thinking that we'd encounter problems like the one you've described as well. I'm starting to think there was a reason we had constrained this check to comparison ops in the past. 😆

[fatkodima]

Catching math ops is nevertheless useful as it can catch bugs like foo(arg1) * foo(arg1), where it should be foo(arg1) * foo(arg2) or foo(arg1) * bar(arg1) or even if it is a heavy function call, should be extracted into a variable and then used as var * var.

I think we should change the cop to ignore cases where lhs and rhs of mathematical operations are simple lvar, ivar, etc.
So y = @x * @x or mentioned var * var or y = x * x * 2 will be ignored.