Add Rake/RequireOutsideTask cop

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#64](https://github.com/rubocop/rubocop-rake/pull/64): Add `Rake/RequireOutsideTask` cop. ([@corsonknowles][])
+
 ### Changes
 
 * [#66](https://github.com/rubocop/rubocop-rake/pull/66): Speed up loading rubocop-rake by lazily loading only the cops needed for a run. This requires RuboCop 1.89.0+. ([@koic][])
@@ -82,3 +86,4 @@
 [@jaruuuu]: https://github.com/jaruuuu
 [@koic]: https://github.com/koic
 [@tejasbubane]: https://github.com/tejasbubane
+[@corsonknowles]: https://github.com/corsonknowles

config/default.yml

@@ -28,3 +28,10 @@ Rake/MethodDefinitionInTask:
   Description: 'Do not define a method in rake task, because it will be defined to the top level.'
   Enabled: true
   VersionAdded: '0.2.0'
+
+Rake/RequireOutsideTask:
+  Description: 'Do not `require` outside of a task block, because it is loaded every time the rake file is loaded.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+  Exclude:
+    - 'Rakefile'

lib/rubocop/cop/rake.rb

@@ -14,6 +14,7 @@ module Rake
       register_cop :DuplicateTask, "#{__dir__}/rake/duplicate_task"
       register_cop :DuplicateNamespace, "#{__dir__}/rake/duplicate_namespace"
       register_cop :MethodDefinitionInTask, "#{__dir__}/rake/method_definition_in_task"
+      register_cop :RequireOutsideTask, "#{__dir__}/rake/require_outside_task"
     end
   end
 end

lib/rubocop/cop/rake/require_outside_task.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rake
+      # Detects `require` and `require_relative` calls that are not inside a
+      # task block.
+      #
+      # A rake file's top level - including the body of a `namespace` block -
+      # is evaluated every time the file is loaded. A require placed there
+      # therefore runs on every rake invocation, instead of only when the task
+      # that needs it runs. Move the require inside the task (or a
+      # `Rake::Task#enhance` block) so the dependency is loaded lazily.
+      #
+      # @example
+      #   # bad
+      #   require 'foo'
+      #
+      #   task :foo do
+      #     Foo.do_something
+      #   end
+      #
+      #   # bad - the namespace body is still evaluated on load
+      #   namespace :foo do
+      #     require 'foo'
+      #
+      #     task :bar do
+      #       Foo.do_something
+      #     end
+      #   end
+      #
+      #   # good
+      #   task :foo do
+      #     require 'foo'
+      #     Foo.do_something
+      #   end
+      #
+      #   # good
+      #   Rake::Task['db:seed'].enhance do
+      #     require 'foo'
+      #     Foo.do_something
+      #   end
+      #
+      class RequireOutsideTask < Base
+        MSG = 'Do not `require` outside of a task block, because it is loaded every time the rake file is loaded.'
+        RESTRICT_ON_SEND = %i[require require_relative].freeze
+
+        # @!method task_block?(node)
+        def_node_matcher :task_block?, <<~PATTERN
+          (block (send nil? :task ...) ...)
+        PATTERN
+
+        # @!method task_enhance_block?(node)
+        def_node_matcher :task_enhance_block?, <<~PATTERN
+          (block
+            (send
+              (send (const (const nil? :Rake) :Task) :[] ...)
+              :enhance ...)
+            ...)
+        PATTERN
+
+        def on_send(node)
+          return if inside_task_block?(node)
+
+          add_offense(node)
+        end
+
+        private def inside_task_block?(node)
+          node.each_ancestor(:block).any? do |ancestor|
+            task_block?(ancestor) || task_enhance_block?(ancestor)
+          end
+        end
+      end
+    end
+  end
+end

spec/lazy_loading_spec.rb

@@ -24,7 +24,7 @@ def run_script(source)
       puts "loaded_cop_files=\#{loaded.size}"
     RUBY
 
-    expect(output).to include('registered=5', 'loaded_cop_files=0')
+    expect(output).to include('registered=6', 'loaded_cop_files=0')
   end
 
   it 'resolves every helper file in `lib/rubocop/cop/rake/helper` through an autoload' do

spec/rubocop/cop/rake/require_outside_task_spec.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rake::RequireOutsideTask, :config do
+  it 'registers an offense for `require` at the top level' do
+    expect_offense(<<~RUBY)
+      require 'foo'
+      ^^^^^^^^^^^^^ Do not `require` outside of a task block, because it is loaded every time the rake file is loaded.
+
+      task :foo do
+        Foo.do_something
+      end
+    RUBY
+  end
+
+  it 'registers an offense for `require_relative` at the top level' do
+    expect_offense(<<~RUBY)
+      require_relative 'foo'
+      ^^^^^^^^^^^^^^^^^^^^^^ Do not `require` outside of a task block, because it is loaded every time the rake file is loaded.
+
+      task :foo do
+      end
+    RUBY
+  end
+
+  it 'registers an offense for `require` inside a namespace but outside a task' do
+    expect_offense(<<~RUBY)
+      namespace :foo do
+        require 'foo'
+        ^^^^^^^^^^^^^ Do not `require` outside of a task block, because it is loaded every time the rake file is loaded.
+
+        task :bar do
+          Foo.do_something
+        end
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for `require` inside a task' do
+    expect_no_offenses(<<~RUBY)
+      task :foo do
+        require 'foo'
+        Foo.do_something
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for `require` inside a `Rake::Task#enhance` block' do
+    expect_no_offenses(<<~RUBY)
+      Rake::Task['db:seed'].enhance do
+        require 'foo'
+        Foo.do_something
+      end
+    RUBY
+  end
+end