From 7e6f9683211d675dae9fd1117b59ad28232a77b8 Mon Sep 17 00:00:00 2001
From: Phil Pirozhkov <pirjsuka@gmail.com>
Date: Fri, 21 Aug 2020 13:31:07 +0300
Subject: [PATCH] Deep dup default confing before letting specs modify it

All cops config:
```ruby
RuboCop::ConfigLoader.default_configuration.for_all_cops.dig('RSpec', 'Language')
```

specifically `for_all_cops` is memoized in `Config`:
```ruby
# rubocop-0.89.1/lib/rubocop/config.rb:132:

def for_all_cops
  @for_all_cops ||= self['AllCops'] || {}
end
```

It's not so obvious to notice, since in this cop the example that is
modifying the language is in its own context, and it runs last. Even if
you add an example after it, due to how RSpec orders examples, it will
still be executed last. However, if you add a `context` with an
example, you'll see that the language changes leaked.

Regular `freeze` and `dup` won't work:

    { 'Language' =>    # <= this is dupped
      { 'Includes' =>  # <= this is the same Hash in the original and dup
        { 'Example' =>
          ['it_behaves_like, 'include_examples', ..., 'it_has_special_behavior']

So, we need to deep dup the default config to avoid config modification
leakages.
---
 .../cop/rspec/empty_example_group_spec.rb     | 16 +++-----------
 .../default_rspec_language_config_context.rb  | 22 +++++++++++++------
 2 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/spec/rubocop/cop/rspec/empty_example_group_spec.rb b/spec/rubocop/cop/rspec/empty_example_group_spec.rb
index 3232c25fc..5a3e8ebfc 100644
--- a/spec/rubocop/cop/rspec/empty_example_group_spec.rb
+++ b/spec/rubocop/cop/rspec/empty_example_group_spec.rb
@@ -212,20 +212,10 @@
   end
 
   context 'when a custom include method is specified' do
-    let(:language) do
-      RuboCop::ConfigLoader
-        .default_configuration
-        .for_all_cops
-        .dig('RSpec', 'Language')
-    end
-    let(:all_cops_config) do
-      cfg = { 'TargetRubyVersion' => ruby_version }
-      cfg['TargetRailsVersion'] = rails_version if rails_version
-      cfg.merge({ 'RSpec' => { 'Language' => language } })
-    end
-
     before do
-      language['Includes']['Example'] << 'it_has_special_behavior'
+      all_cops_config
+        .dig('RSpec', 'Language', 'Includes', 'Example')
+        .push('it_has_special_behavior')
     end
 
     it 'ignores an empty example group with a custom include' do
diff --git a/spec/shared/default_rspec_language_config_context.rb b/spec/shared/default_rspec_language_config_context.rb
index d88deb850..e1fa2cb1e 100644
--- a/spec/shared/default_rspec_language_config_context.rb
+++ b/spec/shared/default_rspec_language_config_context.rb
@@ -4,12 +4,20 @@
   let(:all_cops_config) do
     cfg = { 'TargetRubyVersion' => ruby_version }
     cfg['TargetRailsVersion'] = rails_version if rails_version
-    cfg.merge({
-                'RSpec' => {
-                  'Language' => RuboCop::ConfigLoader
-                                  .default_configuration
-                                  .for_all_cops.dig('RSpec', 'Language')
-                }
-              })
+    default_language = RuboCop::ConfigLoader
+      .default_configuration
+      .for_all_cops.dig('RSpec', 'Language')
+    cfg.merge('RSpec' => { 'Language' => deep_dup(default_language) })
+  end
+
+  def deep_dup(object)
+    case object
+    when Array
+      object.map { |item| deep_dup(item) }
+    when Hash
+      object.transform_values(&method(:deep_dup))
+    else
+      object # only collections undergo modifications and need duping
+    end
   end
 end