Replace ENV[] by ENV.fetch in rubocop project

.rubocop.yml

@@ -42,15 +42,6 @@ Style/IpAddresses:
   Exclude:
     - spec/rubocop/cop/style/ip_addresses_spec.rb
 
-Style/FetchEnvVar:
-  AllowedVars:
-    - HOME
-    - RUBOCOP_CACHE_ROOT
-    - XDG_CACHE_HOME
-    - XDG_CONFIG_HOME
-    - CIRCLE_STAGE
-    - CI
-
 Layout/EndOfLine:
   EnforcedStyle: lf
 

lib/rubocop/cli/command/suggest_extensions.rb

@@ -42,7 +42,7 @@ def skip?
           # 1. On CI
           # 2. When given RuboCop options that it doesn't make sense for
           # 3. For all formatters except specified in `INCLUDED_FORMATTERS'`
-          ENV['CI'] ||
+          ENV.fetch('CI', nil) ||
             @options[:only] || @options[:debug] || @options[:list_target_files] ||
             @options[:out] || @options[:stdin] ||
             !INCLUDED_FORMATTERS.include?(current_formatter)

lib/rubocop/result_cache.rb

@@ -66,14 +66,14 @@ def remove_files(files, dirs, remove_count)
     end
 
     def self.cache_root(config_store)
-      root = ENV['RUBOCOP_CACHE_ROOT']
+      root = ENV.fetch('RUBOCOP_CACHE_ROOT', nil)
       root ||= config_store.for_pwd.for_all_cops['CacheRootDirectory']
       root ||= if ENV.key?('XDG_CACHE_HOME')
                  # Include user ID in the path to make sure the user has write
                  # access.
-                 File.join(ENV['XDG_CACHE_HOME'], Process.uid.to_s)
+                 File.join(ENV.fetch('XDG_CACHE_HOME'), Process.uid.to_s)
                else
-                 File.join(ENV['HOME'], '.cache')
+                 File.join(ENV.fetch('HOME'), '.cache')
                end
       File.join(root, 'rubocop_cache')
     end

lib/rubocop/rspec/shared_contexts.rb

@@ -5,8 +5,8 @@
 RSpec.shared_context 'isolated environment', :isolated_environment do
   around do |example|
     Dir.mktmpdir do |tmpdir|
-      original_home = ENV['HOME']
-      original_xdg_config_home = ENV['XDG_CONFIG_HOME']
+      original_home = ENV.fetch('HOME', nil)
+      original_xdg_config_home = ENV.fetch('XDG_CONFIG_HOME', nil)
 
       # Make sure to expand all symlinks in the path first. Otherwise we may
       # get mismatched pathnames when loading config files later on.

spec/rubocop/cli_spec.rb

@@ -1837,8 +1837,8 @@ def find_suggestions
 
       # Ensure that these specs works in CI, since the feature is generally
       # disabled in when ENV['CI'] is set.
-      allow(ENV).to receive(:[]).and_call_original
-      allow(ENV).to receive(:[]).with('CI').and_return(false)
+      allow(ENV).to receive(:fetch).and_call_original
+      allow(ENV).to receive(:fetch).with('CI', nil).and_return(false)
 
       # Mock the lockfile to be parsed by bundler
       allow(Bundler).to receive(:default_lockfile)
@@ -2024,7 +2024,7 @@ def find_suggestions
     end
 
     context 'when in CI mode' do
-      before { allow(ENV).to receive(:[]).with('CI').and_return(true) }
+      before { allow(ENV).to receive(:fetch).with('CI', nil).and_return(true) }
 
       it 'does not show the suggestion' do
         expect { cli.run(['example.rb']) }.not_to suggest_extensions

spec/rubocop/result_cache_spec.rb

@@ -376,7 +376,7 @@ def abs(path)
 
         it 'contains the given path and UID' do
           cacheroot = described_class.cache_root(config_store)
-          expect(cacheroot).to eq(File.join(ENV['XDG_CACHE_HOME'], puid, 'rubocop_cache'))
+          expect(cacheroot).to eq(File.join(ENV.fetch('XDG_CACHE_HOME'), puid, 'rubocop_cache'))
         end
       end
     end

spec/spec_helper.rb

@@ -70,11 +70,11 @@
 
   config.after(:suite) { RuboCop::Cop::Registry.reset! }
 
-  if %w[ruby-head-ascii_spec ruby-head-spec].include? ENV['CIRCLE_STAGE']
+  if %w[ruby-head-ascii_spec ruby-head-spec].include? ENV.fetch('CIRCLE_STAGE', nil)
     config.filter_run_excluding broken_on: :ruby_head
   end
 
-  if %w[jruby-9.3-ascii_spec jruby-9.3-spec].include? ENV['CIRCLE_STAGE']
+  if %w[jruby-9.3-ascii_spec jruby-9.3-spec].include? ENV.fetch('CIRCLE_STAGE', nil)
     config.filter_run_excluding broken_on: :jruby
   end
 end