[#5977] Warn for Performance Cops

### Summary This PR warns for Performance Cops. The following warning is displayed when the next released rubocop gem is installed. ```console # The following is an example for operation check. % rake build % gem install pkg/rubocop-0.66.0.gem Performance Cops will be removed from RuboCop 0.68. Use rubocop-performance gem instead. Put this in your Gemfile. gem 'rubocop-performance' And then execute: $ bundle install Put this into your .rubocop.yml. require: rubocop-performance More information: https://github.com/rubocop-hq/rubocop-performance Successfully installed rubocop-0.66.0 1 gem installed ``` The following warning is displayed if RuboCop is used with Bundler. ```consle % bundle exec rubocop [Warn] Performance Cops will be removed from RuboCop 0.68. Use rubocop-performance gem instead. https://github.com/rubocop-hq/rubocop/tree/master/manual/migrate_performance_cops.md ``` The above warning will disappear when rubocop-performance gem is written to Gemfile. The rubocop-performance implementation takes precedence when rubocop-performance is written in Gemfile. And I prepared a simple migration manual (migrate_performance_cops.md) because I think that long warning sentences are not preferred. I think that referring to the link is good when runnning rubocop command. ### Other Infromation At first I tried to remove performance cops from RuboCop Core and add rubocop-performance gem as a dependency because of fallback. ```diff % git diff diff --git a/rubocop.gemspec b/rubocop.gemspec index bbbcca33f..09882b063 100644 --- a/rubocop.gemspec +++ b/rubocop.gemspec @@ -38,6 +38,7 @@ Gem::Specification.new do |s| s.add_runtime_dependency('parser', '>= 2.5', '!= 2.5.1.1') s.add_runtime_dependency('psych', '>= 3.1.0') s.add_runtime_dependency('rainbow', '>= 2.2.2', '< 4.0') + s.add_runtime_dependency('rubocop-performance') s.add_runtime_dependency('ruby-progressbar', '~> 1.7') s.add_runtime_dependency('unicode-display_width', '>= 1.4.0', '< 1.6') ``` However, this cannot be resolved because it is cyclic. ```console % bundle install Fetching gem metadata from https://rubygems.org/........ Fetching gem metadata from https://rubygems.org/. Resolving dependencies... Your bundle requires gems that depend on each other, creating an infinite loop. Please remove either gem 'rubocop' or gem 'rubocop-performance' and try again. ``` So I'd like to display a warning before removing performance cops. I'd like to mitigate the impact on users this way. The next step is to remove performance cops and done #5977.
rubocop · Mar 19, 2019 · 698ddeb · smortex · Apr 10, 2019 · 698ddeb
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Changes
+
+* [#5977](https://github.com/rubocop-hq/rubocop/issues/5977): Warn for Performance Cops. ([@koic][])
+
 ## 0.66.0 (2019-03-18)
 
 ### New features

diff --git a/exe/rubocop b/exe/rubocop
@@ -9,6 +9,18 @@ require 'benchmark'
 cli = RuboCop::CLI.new
 result = 0
 
+if defined?(Bundler)
+  gemfile_lock = Bundler.read_file(Bundler.default_lockfile)
+  parser = Bundler::LockfileParser.new(gemfile_lock)
+
+  unless parser.dependencies['rubocop-performance']
+    warn Rainbow(<<-MESSAGE.strip_indent).yellow.to_s
+      [Warn] Performance Cops will be removed from RuboCop 0.68. Use rubocop-performance gem instead.
+             https://github.com/rubocop-hq/rubocop/tree/master/manual/migrate_performance_cops.md
+    MESSAGE
+  end
+end
+
 time = Benchmark.realtime do
   result = cli.run
 end

diff --git a/manual/extensions.md b/manual/extensions.md
@@ -32,6 +32,8 @@ See [development](development.md).
 
 #### Known Custom Cops
 
+* [rubocop-performance](https://github.com/rubocop-hq/rubocop-performance) -
+  Performance optimization analysis
 * [rubocop-rspec](https://github.com/rubocop-hq/rubocop-rspec) -
   RSpec-specific analysis
 * [rubocop-thread_safety](https://github.com/covermymeds/rubocop-thread_safety) -

diff --git a/manual/migrate_performance_cops.md b/manual/migrate_performance_cops.md
@@ -0,0 +1,15 @@
+Performance Cops will be removed from RuboCop 0.68. Use rubocop-performance gem instead.
+
+Put this in your Gemfile.
+
+  gem 'rubocop-performance'
+
+And then execute:
+
+  $ bundle install
+
+Put this into your .rubocop.yml.
+
+  require: rubocop-performance
+
+More information: https://github.com/rubocop-hq/rubocop-performance
diff --git a/rubocop.gemspec b/rubocop.gemspec
@@ -43,4 +43,6 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency('bundler', '>= 1.3.0', '< 3.0')
   s.add_development_dependency('rack', '>= 2.0')
+
+  s.post_install_message = File.read('manual/migrate_performance_cops.md')
 end