Use ConfigLoader.default_configuration for default (#7632)

When the config file path is same as the default config file,
use `ConfigLoader.default_configuration` instead of create a new config.

Because some plugins add their default config values to
`ConfigLoader.default_configuration`. So the Cops of the plugins expect
that default config values exists.

Fix rubocop/rubocop-rails#127

Co-authored-by: Bozhidar Batsov <bozhidar@batsov.com>

CHANGELOG.md

@@ -21,6 +21,7 @@
 * [#7841](https://github.com/rubocop-hq/rubocop/issues/7841): Fix an error for `Style/TrailingCommaInBlockArgs` when lambda literal (`->`) has multiple arguments. ([@koic][])
 * [#7842](https://github.com/rubocop-hq/rubocop/issues/7842): Fix a false positive for `Lint/RaiseException` when Exception without cbase specified under the namespace `Gem` by adding  `AllowedImplicitNamespaces` option. ([@koic][])
 * `Style/IfUnlessModifier` does not infinite-loop when autocorrecting long lines which use if/unless modifiers and have multiple statements separated by semicolons. ([@alexdowad][])
+* [rubocop-hq/rubocop-rails#127](https://github.com/rubocop-hq/rubocop-rails/issues/127): Use `ConfigLoader.default_configuration` for the default config. ([@hanachin][])
 
 ### Changes
 
@@ -4441,6 +4442,7 @@
 [@mangara]: https://github.com/mangara
 [@pirj]: https://github.com/pirj
 [@pawptart]: https://github.com/pawptart
+[@hanachin]: https://github.com/hanachin
 [@cetinajero]: https://github.com/cetinajero
 [@gfyoung]: https://github.com/gfyoung
 [@Tietew]: https://github.com/Tietew
@@ -4455,4 +4457,4 @@
 [@rafaelfranca]: https://github.com/rafaelfranca
 [@knu]: https://github.com/knu
 [@saurabhmaurya15]: https://github.com/saurabhmaurya15
-[@DracoAter]: https://github.com/DracoAter
+[@DracoAter]: https://github.com/DracoAter

lib/rubocop/config_loader.rb

@@ -84,9 +84,9 @@ def configuration_file_for(target_dir)
       end
 
       def configuration_from_file(config_file)
-        config = load_file(config_file)
-        return config if config_file == DEFAULT_FILE
+        return ConfigLoader.default_configuration if config_file == DEFAULT_FILE
 
+        config = load_file(config_file)
         if ignore_parent_exclusion?
           print 'Ignoring AllCops/Exclude from parent folders' if debug?
         else

spec/rubocop/cli/cli_options_spec.rb

@@ -671,7 +671,7 @@ class SomeCop < Cop
       home = File.dirname(File.dirname(File.dirname(File.dirname(__FILE__))))
       expect($stdout.string.lines.grep(/configuration/).map(&:chomp))
         .to eq(["For #{abs('')}:" \
-                " configuration from #{home}/config/default.yml"])
+                " Default configuration from #{home}/config/default.yml"])
     end
 
     it 'shows cop names' do

spec/support/cli_spec_behavior.rb

@@ -11,6 +11,7 @@ def abs(path)
 
   before do
     RuboCop::ConfigLoader.debug = false
+    RuboCop::ConfigLoader.default_configuration = nil
 
     # OPTIMIZE: Makes these specs faster. Work directory (the parent of
     # .rubocop_cache) is removed afterwards anyway.