Fix inherit_mode for arrays in extension default

See rubocop/rubocop-rspec#1126

`config/default.yml`:
```yaml
RSpec:
  Language:
    Examples:
      inherit_mode:
        merge:
          - Regular
      Regular:
        - it
        - specify
        - example
        - scenario
        - its
```

`.rubocop.yml`:
```yaml
require:
  - rubocop-rspec

RSpec:
  Language:
    Examples:
      Regular:
        - mycustomexamplealias
```

Previously, locally-set `inherit_mode` in extension default
configuration was not respected.

changelog/fix_inherit_mode-for-extensions.md

@@ -0,0 +1 @@
+* [#9952](https://github.com/rubocop/rubocop/pull/9952) [rubocop-rspec#1126](https://github.com/rubocop/rubocop-rspec/issues/1126): Fix `inherit_mode` for deeply nested configuration defined in extensions' default configuration. ([@pirj][])

lib/rubocop/config_loader_resolver.rb

@@ -108,7 +108,7 @@ def merge(base_hash, derived_hash, **opts)
           result.delete(key)
         elsif merge_hashes?(base_hash, derived_hash, key)
           result[key] = merge(base_hash[key], derived_hash[key], **opts)
-        elsif should_union?(base_hash, key, opts[:inherit_mode])
+        elsif should_union?(derived_hash, base_hash, opts[:inherit_mode], key)
           result[key] = base_hash[key] | derived_hash[key]
         elsif opts[:debug]
           warn_on_duplicate_setting(base_hash, derived_hash, key, **opts)
@@ -183,11 +183,26 @@ def determine_inherit_mode(hash, key)
       local_inherit || hash['inherit_mode'] || {}
     end
 
-    def should_union?(base_hash, key, inherit_mode)
-      base_hash[key].is_a?(Array) &&
-        inherit_mode &&
-        inherit_mode['merge'] &&
-        inherit_mode['merge'].include?(key)
+    def should_union?(derived_hash, base_hash, root_mode, key)
+      return false unless base_hash[key].is_a?(Array)
+
+      derived_mode = derived_hash['inherit_mode']
+      return false if should_override?(derived_mode, key)
+      return true if should_merge?(derived_mode, key)
+
+      base_mode = base_hash['inherit_mode']
+      return false if should_override?(base_mode, key)
+      return true if should_merge?(base_mode, key)
+
+      should_merge?(root_mode, key)
+    end
+
+    def should_merge?(mode, key)
+      mode && mode['merge'] && mode['merge'].include?(key)
+    end
+
+    def should_override?(mode, key)
+      mode && mode['override'] && mode['override'].include?(key)
     end
 
     def merge_hashes?(base_hash, derived_hash, key)

spec/rubocop/config_loader_spec.rb

@@ -537,6 +537,59 @@
       end
     end
 
+    context 'when inherit_mode is specified for a nested element even ' \
+            'without explicitly specifying `inherit_from`/`inherit_gem`' do
+      let(:file_path) { '.rubocop.yml' }
+
+      before do
+        stub_const('RuboCop::ConfigLoader::RUBOCOP_HOME', 'rubocop')
+        stub_const('RuboCop::ConfigLoader::DEFAULT_FILE',
+                   File.join('rubocop', 'config', 'default.yml'))
+
+        create_file('rubocop/config/default.yml', <<~YAML)
+          Language:
+            Examples:
+              inherit_mode:
+                merge:
+                  - Regular
+                  - Focused
+              Regular:
+                - it
+              Focused:
+                - fit
+              Skipped:
+                - xit
+              Pending:
+                - pending
+        YAML
+        create_file(file_path, <<~YAML)
+          Language:
+            Examples:
+              inherit_mode:
+                merge:
+                  - Skipped
+                override:
+                  - Focused
+              Regular:
+                - scenario
+              Focused:
+                - fscenario
+              Skipped:
+                - xscenario
+              Pending:
+                - later
+        YAML
+      end
+
+      it 'respects the priority of `inherit_mode`, user-defined first' do
+        examples_configuration = configuration_from_file['Language']['Examples']
+        expect(examples_configuration['Regular']).to contain_exactly('it', 'scenario')
+        expect(examples_configuration['Focused']).to contain_exactly('fscenario')
+        expect(examples_configuration['Skipped']).to contain_exactly('xit', 'xscenario')
+        expect(examples_configuration['Pending']).to contain_exactly('later')
+      end
+    end
+
     context 'when a department is disabled', :restore_registry do
       let(:file_path) { '.rubocop.yml' }