Add Performance::NumericPredicate cop

changelog/new_add_performancemumericpredicate_cop.md

@@ -0,0 +1 @@
+* [#440](https://github.com/rubocop/rubocop-performance/pull/440): Add Performance::NumericPredicate cop. ([@miry][])

config/default.yml

@@ -205,6 +205,12 @@ Performance/MethodObjectAsBlock:
   Enabled: pending
   VersionAdded: '1.9'
 
+Performance/NumericPredicate:
+  Description: 'Use compare operator instead of `Numeric#positive?`, `Numeric#negative?`, or `Numeric#zero?`.'
+  Enabled: pending
+  Safe: false
+  VersionAdded: '<<next>>'
+
 Performance/OpenStruct:
   Description: 'Use `Struct` instead of `OpenStruct`.'
   Enabled: false

lib/rubocop/cop/performance/numeric_predicate.rb

@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Performance
+      # Identifies places where numeric uses predicates `positive?`, and `negative?` should be
+      # converted to compare operator.
+      #
+      # @safety
+      #   This cop is unsafe because it cannot be guaranteed that the receiver
+      #   defines the predicates or can be compared to a number, which may lead
+      #   to a false positive for non-standard classes.
+      #
+      # @example
+      #   # bad
+      #   1.positive?
+      #   1.43.negative?
+      #   -4.zero?
+      #
+      #   # good
+      #   1 > 0
+      #   1.43 < 0.0
+      #   -4 == 0
+      #
+      class NumericPredicate < Base
+        extend AutoCorrector
+
+        MSG = 'Use compare operator `%<good>s` instead of `%<bad>s`.'
+        RESTRICT_ON_SEND = %i[positive? zero? negative?].freeze
+        REPLACEMENTS = { negative?: '<', positive?: '>', zero?: '==' }.freeze
+
+        def_node_matcher :num_predicate?, <<~PATTERN
+          (send $numeric_type? ${:negative? :positive? :zero?})
+        PATTERN
+
+        def_node_matcher :instance_predicate?, <<~PATTERN
+          (send $!nil? ${:negative? :positive?})
+        PATTERN
+
+        def on_send(node)
+          return unless num_predicate?(node) || instance_predicate?(node)
+          return unless node.receiver
+
+          good_method = build_good_method(node.receiver, node.method_name)
+          message = format(MSG, good: good_method, bad: node.source)
+          add_offense(node, message: message) do |corrector|
+            corrector.replace(node, good_method)
+          end
+        end
+
+        private
+
+        def build_good_method(receiver, method)
+          operation = REPLACEMENTS[method]
+          zero = receiver&.float_type? ? 0.0 : 0
+          "#{receiver.source} #{operation} #{zero}"
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/performance_cops.rb

@@ -27,6 +27,7 @@
 require_relative 'performance/map_compact'
 require_relative 'performance/map_method_chain'
 require_relative 'performance/method_object_as_block'
+require_relative 'performance/numeric_predicate'
 require_relative 'performance/open_struct'
 require_relative 'performance/range_include'
 require_relative 'performance/io_readlines'

spec/rubocop/cop/performance/numeric_predicate_spec.rb

@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Performance::NumericPredicate, :config do
+  let(:message) { RuboCop::Cop::Performance::NumericPredicate::MSG }
+
+  shared_examples 'common functionality' do |method, op|
+    it 'for integer' do
+      expect_offense(<<~RUBY, method: method)
+        1.#{method}
+        ^^^{method} Use compare operator `1 #{op} 0` instead of `1.#{method}`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        1 #{op} 0
+      RUBY
+    end
+
+    it 'for float' do
+      expect_offense(<<~RUBY, method: method)
+        1.2.#{method}
+        ^^^^^{method} Use compare operator `1.2 #{op} 0.0` instead of `1.2.#{method}`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        1.2 #{op} 0.0
+      RUBY
+    end
+
+    it 'ignore big decimal' do
+      next if method == 'zero?'
+
+      expect_offense(<<~RUBY, method: method)
+        BigDecimal('1', 2).#{method}
+        ^^^^^^^^^^^^^^^^^^^^{method} Use compare operator `BigDecimal('1', 2) #{op} 0` instead of `BigDecimal('1', 2).#{method}`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        BigDecimal('1', 2) #{op} 0
+      RUBY
+    end
+
+    it 'for variable' do
+      next if method == 'zero?'
+
+      expect_offense(<<~RUBY, method: method)
+        foo = 1
+        foo.#{method}
+        ^^^^^{method} Use compare operator `foo #{op} 0` instead of `foo.#{method}`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        foo = 1
+        foo #{op} 0
+      RUBY
+    end
+
+    it 'in condition statements' do
+      next if method == 'zero?'
+
+      expect_offense(<<~RUBY, method: method)
+        foo = 1
+        if foo.#{method}
+           ^^^^^{method} Use compare operator `foo #{op} 0` instead of `foo.#{method}`.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        foo = 1
+        if foo #{op} 0
+        end
+      RUBY
+    end
+
+    it 'in map statement' do
+      next if method == 'zero?'
+
+      expect_no_offenses(<<~RUBY, method: method)
+        foo = [1, 2, 3]
+        if foo.all?(&:#{method})
+        end
+      RUBY
+    end
+  end
+
+  it_behaves_like 'common functionality', 'positive?', '>'
+  it_behaves_like 'common functionality', 'negative?', '<'
+  it_behaves_like 'common functionality', 'zero?', '=='
+end