Lint that const_get uses false as 2nd arg

The default of inherit=true as the 2nd arg for const_get leads to some
confusing situations when `const_get` is called in development where
some modules are not yet loaded.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/59719 for examples.

rubocop/cop/const_get_inherit_false.rb

+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Cop that encourages usage of inherit=false for 2nd argument when using const_get.
+    #
+    # See https://gitlab.com/gitlab-org/gitlab-ce/issues/59719
+    class ConstGetInheritFalse < RuboCop::Cop::Cop
+      MSG = 'Use inherit=false when using const_get.'
+
+      def_node_matcher :const_get?, <<~PATTERN
+        (send _ :const_get ...)
+      PATTERN
+
+      def on_send(node)
+        return unless const_get?(node)
+        return if second_argument(node)&.false_type?
+
+        add_offense(node, location: :selector)
+      end
+
+      def autocorrect(node)
+        lambda do |corrector|
+          if arg = second_argument(node)
+            corrector.replace(arg.source_range, 'false')
+          else
+            first_argument = node.arguments[0]
+            corrector.insert_after(first_argument.source_range, ', false')
+          end
+        end
+      end
+
+      private
+
+      def second_argument(node)
+        node.arguments[1]
+      end
+    end
+  end
+end

rubocop/rubocop.rb

@@ -11,6 +11,7 @@ require_relative 'cop/active_record_association_reload'
 require_relative 'cop/avoid_return_from_blocks'
 require_relative 'cop/avoid_break_from_strong_memoize'
 require_relative 'cop/avoid_route_redirect_leading_slash'
+require_relative 'cop/const_get_inherit_false'
 require_relative 'cop/line_break_around_conditional_block'
 require_relative 'cop/prefer_class_methods_over_module'
 require_relative 'cop/migration/add_column'

spec/rubocop/cop/const_get_inherit_false_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../rubocop/cop/const_get_inherit_false'
+
+describe RuboCop::Cop::ConstGetInheritFalse do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  context 'Object.const_get' do
+    it 'registers an offense with no 2nd argument' do
+      expect_offense(<<~PATTERN.strip_indent)
+        Object.const_get(:CONSTANT)
+               ^^^^^^^^^ Use inherit=false when using const_get.
+      PATTERN
+    end
+
+    it 'autocorrects' do
+      expect(autocorrect_source('Object.const_get(:CONSTANT)')).to eq('Object.const_get(:CONSTANT, false)')
+    end
+
+    context 'inherit=false' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~PATTERN.strip_indent)
+        Object.const_get(:CONSTANT, false)
+        PATTERN
+      end
+    end
+
+    context 'inherit=true' do
+      it 'registers an offense' do
+        expect_offense(<<~PATTERN.strip_indent)
+        Object.const_get(:CONSTANT, true)
+               ^^^^^^^^^ Use inherit=false when using const_get.
+        PATTERN
+      end
+
+      it 'autocorrects' do
+        expect(autocorrect_source('Object.const_get(:CONSTANT, true)')).to eq('Object.const_get(:CONSTANT, false)')
+      end
+    end
+  end
+
+  context 'const_get for a nested class' do
+    it 'registers an offense on reload usage' do
+      expect_offense(<<~PATTERN.strip_indent)
+        Nested::Blog.const_get(:CONSTANT)
+                     ^^^^^^^^^ Use inherit=false when using const_get.
+      PATTERN
+    end
+
+    it 'autocorrects' do
+      expect(autocorrect_source('Nested::Blag.const_get(:CONSTANT)')).to eq('Nested::Blag.const_get(:CONSTANT, false)')
+    end
+
+    context 'inherit=false' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~PATTERN.strip_indent)
+        Nested::Blog.const_get(:CONSTANT, false)
+        PATTERN
+      end
+    end
+
+    context 'inherit=true' do
+      it 'registers an offense if inherit is true' do
+        expect_offense(<<~PATTERN.strip_indent)
+        Nested::Blog.const_get(:CONSTANT, true)
+                     ^^^^^^^^^ Use inherit=false when using const_get.
+        PATTERN
+      end
+
+      it 'autocorrects' do
+        expect(autocorrect_source('Nested::Blag.const_get(:CONSTANT, true)')).to eq('Nested::Blag.const_get(:CONSTANT, false)')
+      end
+    end
+  end
+end