Add new Lint/BinaryOperatorIdenticalOperands cop

CHANGELOG.md

@@ -7,6 +7,7 @@
 * [#8322](https://github.com/rubocop-hq/rubocop/pull/8322): Support autocorrect for `Style/CaseEquality` cop. ([@fatkodima][])
 * [#8291](https://github.com/rubocop-hq/rubocop/pull/8291): Add new `Lint/SelfAssignment` cop. ([@fatkodima][])
 * [#8389](https://github.com/rubocop-hq/rubocop/pull/8389): Add new `Lint/DuplicateRescueException` cop. ([@fatkodima][])
+* [#8433](https://github.com/rubocop-hq/rubocop/pull/8433): Add new `Lint/BinaryOperatorWithIdenticalOperands` cop. ([@fatkodima][])
 * [#8430](https://github.com/rubocop-hq/rubocop/pull/8430): Add new `Lint/UnreachableLoop` cop. ([@fatkodima][])
 * [#8412](https://github.com/rubocop-hq/rubocop/pull/8412): Add new `Style/OptionalBooleanParameter` cop. ([@fatkodima][])
 * [#8432](https://github.com/rubocop-hq/rubocop/pull/8432): Add new `Lint/FloatComparison` cop. ([@fatkodima][])
@@ -45,6 +46,7 @@
 ### Changes
 
 * [#8376](https://github.com/rubocop-hq/rubocop/pull/8376): `Style/MethodMissingSuper` cop is removed in favor of new `Lint/MissingSuper` cop. ([@fatkodima][])
+* [#8433](https://github.com/rubocop-hq/rubocop/pull/8433): `Lint/UselessComparison` cop is removed in favor of new `Lint/BinaryOperatorWithIdenticalOperands` cop. ([@fatkodima][])
 * [#8350](https://github.com/rubocop-hq/rubocop/pull/8350): Set default max line length to 120 for `Style/MultilineMethodSignature`. ([@koic][])
 * [#8338](https://github.com/rubocop-hq/rubocop/pull/8338): **potentially breaking**. Config#for_department now returns only the config specified for that department; the 'Enabled' attribute is no longer calculated. ([@marcandre][])
 * [#8037](https://github.com/rubocop-hq/rubocop/pull/8037): **(Breaking)** Cop `Metrics/AbcSize` now counts ||=, &&=, multiple assignments, for, yield, iterating blocks. `&.` now count as conditions too (unless repeated on the same variable). Default bumped from 15 to 17. Consider using `rubocop -a --disable-uncorrectable` to ease transition. ([@marcandre][])

config/default.yml

@@ -1355,6 +1355,12 @@ Lint/BigDecimalNew:
   Enabled: true
   VersionAdded: '0.53'
 
+Lint/BinaryOperatorWithIdenticalOperands:
+  Description: 'This cop checks for places where binary operator has identical operands.'
+  Enabled: pending
+  Safe: false
+  VersionAdded: '0.89'
+
 Lint/BooleanSymbol:
   Description: 'Check for `:true` and `:false` symbols.'
   Enabled: true
@@ -1906,11 +1912,6 @@ Lint/UselessAssignment:
   Enabled: true
   VersionAdded: '0.11'
 
-Lint/UselessComparison:
-  Description: 'Checks for comparison of something with itself.'
-  Enabled: true
-  VersionAdded: '0.11'
-
 Lint/UselessElseWithoutRescue:
   Description: 'Checks for useless `else` in `begin..end` without `rescue`.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -185,6 +185,7 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#lintambiguousregexpliteral[Lint/AmbiguousRegexpLiteral]
 * xref:cops_lint.adoc#lintassignmentincondition[Lint/AssignmentInCondition]
 * xref:cops_lint.adoc#lintbigdecimalnew[Lint/BigDecimalNew]
+* xref:cops_lint.adoc#lintbinaryoperatorwithidenticaloperands[Lint/BinaryOperatorWithIdenticalOperands]
 * xref:cops_lint.adoc#lintbooleansymbol[Lint/BooleanSymbol]
 * xref:cops_lint.adoc#lintcircularargumentreference[Lint/CircularArgumentReference]
 * xref:cops_lint.adoc#lintconstantresolution[Lint/ConstantResolution]
@@ -269,7 +270,6 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#linturiregexp[Lint/UriRegexp]
 * xref:cops_lint.adoc#lintuselessaccessmodifier[Lint/UselessAccessModifier]
 * xref:cops_lint.adoc#lintuselessassignment[Lint/UselessAssignment]
-* xref:cops_lint.adoc#lintuselesscomparison[Lint/UselessComparison]
 * xref:cops_lint.adoc#lintuselesselsewithoutrescue[Lint/UselessElseWithoutRescue]
 * xref:cops_lint.adoc#lintuselesssettercall[Lint/UselessSetterCall]
 * xref:cops_lint.adoc#lintvoid[Lint/Void]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -211,6 +211,46 @@ BigDecimal.new(123.456, 3)
 BigDecimal(123.456, 3)
 ----
 
+== Lint/BinaryOperatorWithIdenticalOperands
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| No
+| No
+| 0.89
+| -
+|===
+
+This cop checks for places where binary operator has identical operands.
+
+It covers arithmetic operators: `+`, `-`, `*`, `/`, `%`, `**`;
+comparison operators: `==`, `===`, `=~`, `>`, `>=`, `<`, `<=`;
+bitwise operators: `|`, `^`, `&`, `<<`, `>>`;
+boolean operators: `&&`, `||`
+and "spaceship" operator - `<=>`.
+
+This cop is marked as unsafe as it does not consider side effects when calling methods
+and thus can generate false positives:
+  if wr.take_char == '\0' && wr.take_char == '\0'
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+x.top >= x.top
+
+if a.x != 0 && a.x != 0
+  do_something
+end
+
+def childs?
+  left_child || left_child
+end
+----
+
 == Lint/BooleanSymbol
 
 |===
@@ -4282,29 +4322,6 @@ end
 
 * https://rubystyle.guide#underscore-unused-vars
 
-== Lint/UselessComparison
-
-|===
-| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
-
-| Enabled
-| Yes
-| No
-| 0.11
-| -
-|===
-
-This cop checks for comparison of something with itself.
-
-=== Examples
-
-[source,ruby]
-----
-# bad
-
-x.top >= x.top
-----
-
 == Lint/UselessElseWithoutRescue
 
 |===

lib/rubocop.rb

@@ -242,6 +242,7 @@
 require_relative 'rubocop/cop/lint/ambiguous_regexp_literal'
 require_relative 'rubocop/cop/lint/assignment_in_condition'
 require_relative 'rubocop/cop/lint/big_decimal_new'
+require_relative 'rubocop/cop/lint/binary_operator_with_identical_operands'
 require_relative 'rubocop/cop/lint/boolean_symbol'
 require_relative 'rubocop/cop/lint/circular_argument_reference'
 require_relative 'rubocop/cop/lint/constant_resolution'
@@ -326,7 +327,6 @@
 require_relative 'rubocop/cop/lint/uri_regexp'
 require_relative 'rubocop/cop/lint/useless_access_modifier'
 require_relative 'rubocop/cop/lint/useless_assignment'
-require_relative 'rubocop/cop/lint/useless_comparison'
 require_relative 'rubocop/cop/lint/useless_else_without_rescue'
 require_relative 'rubocop/cop/lint/useless_setter_call'
 require_relative 'rubocop/cop/lint/void'

lib/rubocop/config_obsoletion.rb

@@ -86,7 +86,10 @@ class ConfigObsoletion
         'it was a duplicate of `Layout/SpaceBeforeFirstArg`. Please use ' \
         '`Layout/SpaceBeforeFirstArg` instead',
       'Style/MethodMissingSuper' => 'it has been superseded by `Lint/MissingSuper`. Please use ' \
-        '`Lint/MissingSuper` instead'
+        '`Lint/MissingSuper` instead',
+      'Lint/UselessComparison' => 'it has been superseded by '\
+        '`Lint/BinaryOperatorWithIdenticalOperands`. Please use '\
+        '`Lint/BinaryOperatorWithIdenticalOperands` instead'
     }.map do |cop_name, reason|
       [cop_name, "The `#{cop_name}` cop has been removed since #{reason}."]
     end

lib/rubocop/cop/lint/binary_operator_with_identical_operands.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for places where binary operator has identical operands.
+      #
+      # It covers arithmetic operators: `+`, `-`, `*`, `/`, `%`, `**`;
+      # comparison operators: `==`, `===`, `=~`, `>`, `>=`, `<`, `<=`;
+      # bitwise operators: `|`, `^`, `&`, `<<`, `>>`;
+      # boolean operators: `&&`, `||`
+      # and "spaceship" operator - `<=>`.
+      #
+      # This cop is marked as unsafe as it does not consider side effects when calling methods
+      # and thus can generate false positives:
+      #   if wr.take_char == '\0' && wr.take_char == '\0'
+      #
+      # @example
+      #   # bad
+      #   x.top >= x.top
+      #
+      #   if a.x != 0 && a.x != 0
+      #     do_something
+      #   end
+      #
+      #   def childs?
+      #     left_child || left_child
+      #   end
+      #
+      class BinaryOperatorWithIdenticalOperands < Base
+        MSG = 'Binary operator `%<op>s` has identical operands.'
+
+        def on_send(node)
+          return unless node.binary_operation?
+
+          lhs, operation, rhs = *node
+          return if node.arithmetic_operation? && lhs.basic_literal? && rhs.basic_literal?
+
+          add_offense(node, message: format(MSG, op: operation)) if lhs == rhs
+        end
+
+        def on_and(node)
+          add_offense(node, message: format(MSG, op: node.operator)) if node.lhs == node.rhs
+        end
+        alias on_or on_and
+      end
+    end
+  end
+end

spec/rubocop/config_obsoletion_spec.rb

@@ -70,6 +70,7 @@
           'Layout/SpaceBeforeModifierKeyword' => { 'Enabled': true },
           'Lint/InvalidCharacterLiteral' => { 'Enabled': true },
           'Style/MethodMissingSuper' => { 'Enabled': true },
+          'Lint/UselessComparison' => { 'Enabled': true },
           'Lint/RescueWithoutErrorClass' => { 'Enabled': true },
           'Lint/SpaceBeforeFirstArg' => { 'Enabled': true },
           'Style/SpaceAfterControlKeyword' => { 'Enabled': true },
@@ -199,6 +200,8 @@
           (obsolete configuration found in example/.rubocop.yml, please update it)
           The `Style/MethodMissingSuper` cop has been removed since it has been superseded by `Lint/MissingSuper`. Please use `Lint/MissingSuper` instead.
           (obsolete configuration found in example/.rubocop.yml, please update it)
+          The `Lint/UselessComparison` cop has been removed since it has been superseded by `Lint/BinaryOperatorWithIdenticalOperands`. Please use `Lint/BinaryOperatorWithIdenticalOperands` instead.
+          (obsolete configuration found in example/.rubocop.yml, please update it)
           The `Style/MethodMissing` cop has been split into `Style/MethodMissingSuper` and `Style/MissingRespondToMissing`.
           (obsolete configuration found in example/.rubocop.yml, please update it)
         OUTPUT

spec/rubocop/cop/lint/binary_operator_with_identical_operands_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::BinaryOperatorWithIdenticalOperands do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense when binary operator has identical nodes' do
+    offenses = inspect_source(<<~RUBY)
+      x == x
+      y = x && x
+      y = a.x + a.x
+      a.x(arg) > a.x(arg)
+      a.(x) > a.(x)
+    RUBY
+
+    expect(offenses.size).to eq(5)
+  end
+
+  it 'does not register an offense when using binary operator with different operands' do
+    expect_no_offenses(<<~RUBY)
+      x == y
+      y = x && z
+      y = a.x + b.x
+      a.x(arg) > b.x(arg)
+      a.(x) > b.(x)
+    RUBY
+  end
+
+  it 'does not register an offense when using arithmetic operator with numerics' do
+    expect_no_offenses(<<~RUBY)
+      x = 2 + 2
+    RUBY
+  end
+end