Add new UnifiedInteger cop (rubocop#3492)

CHANGELOG.md

@@ -15,6 +15,7 @@
 * Add check for `persisted?` method call when using a create method in `Rails/SaveBang`. ([@QuinnHarris][])
 * Add new `Style/SafeNavigation` cop to convert method calls safeguarded by a non `nil` check for the object to `&.`. ([@rrosenblum][])
 * Add new `Performance/SortWithBlock` cop to use `sort_by(&:foo)` instead of `sort_by { |a, b| a.foo <=> b.foo }`. ([@koic][])
+* [#3492](https://github.com/bbatsov/rubocop/pull/3492): Add new `UnifiedInteger` cop. ([@pocke][])
 
 ### Bug fixes
 

config/enabled.yml

@@ -1209,6 +1209,10 @@ Lint/UnderscorePrefixedVariableName:
   Description: 'Do not use prefix `_` for a variable that is used.'
   Enabled: true
 
+Lint/UnifiedInteger:
+  Description: 'Use Integer instead of Fixnum or Bignum'
+  Enabled: true
+
 Lint/UnneededDisable:
   Description: >-
                  Checks for rubocop:disable comments that can be removed.

lib/rubocop.rb

@@ -134,6 +134,7 @@
 require 'rubocop/cop/lint/string_conversion_in_interpolation'
 require 'rubocop/cop/lint/syntax'
 require 'rubocop/cop/lint/underscore_prefixed_variable_name'
+require 'rubocop/cop/lint/unified_integer'
 require 'rubocop/cop/lint/unneeded_disable'
 require 'rubocop/cop/lint/unneeded_splat_expansion'
 require 'rubocop/cop/lint/unreachable_code'

lib/rubocop/cop/lint/unified_integer.rb

@@ -0,0 +1,38 @@
+# encoding: utf-8
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for using Fixnum or Bignum constant.
+      #
+      # @example
+      #   # bad
+      #   1.is_a?(Fixnum)
+      #   1.is_a?(Bignum)
+      #
+      #   # good
+      #   1.is_a?(Integer)
+      class UnifiedInteger < Cop
+        MSG = 'Use `Integer` instead of `%s`.'.freeze
+
+        def_node_matcher :fixnum_or_bignum_const?, <<-PATTERN
+          (:const {nil (:cbase)} ${:Fixnum :Bignum})
+        PATTERN
+
+        def on_const(node)
+          klass = fixnum_or_bignum_const?(node)
+          return unless klass
+
+          add_offense(node, :expression, format(MSG, klass))
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            corrector.replace(node.loc.name, 'Integer')
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/unified_integer_spec.rb

@@ -0,0 +1,72 @@
+# encoding: utf-8
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe RuboCop::Cop::Lint::UnifiedInteger do
+  let(:config) { RuboCop::Config.new }
+  subject(:cop) { described_class.new(config) }
+
+  shared_examples 'registers an offence' do |klass|
+    context "when #{klass}" do
+      context 'without any decorations' do
+        let(:source) { "1.is_a?(#{klass})" }
+
+        it 'registers an offence' do
+          inspect_source(cop, source)
+          expect(cop.offenses.size).to eq(1)
+          expect(cop.messages).to eq(["Use `Integer` instead of `#{klass}`."])
+        end
+
+        it 'autocorrects' do
+          new_source = autocorrect_source(cop, source)
+          expect(new_source).to eq('1.is_a?(Integer)')
+        end
+      end
+
+      context 'when explicitly specified as toplevel constant' do
+        let(:source) { "1.is_a?(::#{klass})" }
+
+        it 'registers an offence' do
+          inspect_source(cop, source)
+          expect(cop.offenses.size).to eq(1)
+          expect(cop.messages).to eq(["Use `Integer` instead of `#{klass}`."])
+        end
+
+        it 'autocorrects' do
+          new_source = autocorrect_source(cop, source)
+          expect(new_source).to eq('1.is_a?(::Integer)')
+        end
+      end
+
+      context 'with MyNamespace' do
+        let(:source) { "1.is_a?(MyNamespace::#{klass})" }
+
+        include_examples 'accepts'
+      end
+    end
+  end
+
+  include_examples 'registers an offence', 'Fixnum'
+  include_examples 'registers an offence', 'Bignum'
+
+  context 'when Integer' do
+    context 'without any decorations' do
+      let(:source) { '1.is_a?(Integer)' }
+
+      include_examples 'accepts'
+    end
+
+    context 'when explicitly specified as toplevel constant' do
+      let(:source) { '1.is_a?(::Integer)' }
+
+      include_examples 'accepts'
+    end
+
+    context 'with MyNamespace' do
+      let(:source) { '1.is_a?(MyNamespace::Integer)' }
+
+      include_examples 'accepts'
+    end
+  end
+end