[Fix #10026] Fix inherit_mode resolution for parent and default config

The problem was that we deleted the `inherit_mode` entry in the
configuration hash while processing the resolution of inheritance from
base configurations (`inherit_from`, etc.). When the merging of default
configuration and user configuration was done at a later stage, the
`inherit_mode` parameter was gone.

By not deleting `inherit_mode`, we fix the problem. I don't think it
has any unwanted side effects, but `inherit_mode` does show up in the
output from `--show-cops` now. This should be OK.

changelog/fix_inherit_mode_resolution.md

@@ -0,0 +1 @@
+* [#10026](https://github.com/rubocop/rubocop/issues/10026): Fix merging of array parameters in either parent of default config. ([@jonas054][])

lib/rubocop/config_loader_resolver.rb

@@ -179,7 +179,7 @@ def warn_on_duplicate_setting(base_hash, derived_hash, key, **opts)
 
     def determine_inherit_mode(hash, key)
       cop_cfg = hash[key]
-      local_inherit = cop_cfg.delete('inherit_mode') if cop_cfg.is_a?(Hash)
+      local_inherit = cop_cfg['inherit_mode'] if cop_cfg.is_a?(Hash)
       local_inherit || hash['inherit_mode'] || {}
     end
 

spec/rubocop/cli/options_spec.rb

@@ -1203,8 +1203,16 @@ def on_send(node)
       create_file('.rubocop.yml', <<~YAML)
         Layout/LineLength:
           Max: 110
+        Lint/DeprecatedConstants:
+          inherit_mode:
+            merge:
+              - DeprecatedConstants
+          DeprecatedConstants:
+            MY_CONST:
+              Alternative: 'MyConst'
+              DeprecatedVersion: '2.7'
       YAML
-      # expect(cli.run(['--show-cops'] + arguments)).to eq(0)
+
       cli.run(['--show-cops'] + arguments)
     end
 
@@ -1277,6 +1285,43 @@ def full_description_of_cop(cop)
       include_examples 'prints config'
     end
 
+    context 'with one cop given and inherit_mode set in its local configuration' do
+      let(:arguments) { ['Lint/DeprecatedConstants'] }
+
+      it 'prints that cop including inherit_mode' do
+        expect(stdout).to match(
+          ['# Supports --autocorrect',
+           'Lint/DeprecatedConstants:',
+           '  Description: Checks for deprecated constants.',
+           '  Enabled: pending',
+           /^  VersionAdded: '[0-9.]+'$/,
+           /^  VersionChanged: '[0-9.]+'$/,
+           '  DeprecatedConstants:',
+           '    NIL:',
+           '      Alternative: nil',
+           "      DeprecatedVersion: '2.4'",
+           "    'TRUE':",
+           "      Alternative: 'true'",
+           "      DeprecatedVersion: '2.4'",
+           "    'FALSE':",
+           "      Alternative: 'false'",
+           "      DeprecatedVersion: '2.4'",
+           '    Net::HTTPServerException:',
+           '      Alternative: Net::HTTPClientException',
+           "      DeprecatedVersion: '2.6'",
+           '    Random::DEFAULT:',
+           '      Alternative: Random.new',
+           "      DeprecatedVersion: '3.0'",
+           '    MY_CONST:',
+           '      Alternative: MyConst',
+           "      DeprecatedVersion: '2.7'",
+           '  inherit_mode:',
+           '    merge:',
+           '    - DeprecatedConstants'].join("\n")
+        )
+      end
+    end
+
     context 'with two cops given' do
       let(:arguments) { ['Layout/IndentationStyle,Layout/LineLength'] }
 

spec/rubocop/config_loader_spec.rb

@@ -590,6 +590,51 @@
       end
     end
 
+    context 'when inherit_mode:merge for a cop lists parameters that are either in parent or in ' \
+            'default configuration' do
+      let(:file_path) { '.rubocop.yml' }
+
+      before do
+        create_file('hosted_config.yml', <<~YAML)
+          AllCops:
+            NewCops: enable
+
+          Naming/VariableNumber:
+            EnforcedStyle: snake_case
+            Exclude:
+              - foo.rb
+            Include:
+              - bar.rb
+        YAML
+        create_file(file_path, <<~YAML)
+          inherit_from:
+            - hosted_config.yml
+
+          Naming/VariableNumber:
+            inherit_mode:
+              merge:
+                - AllowedIdentifiers
+                - Exclude
+                - Include
+            AllowedIdentifiers:
+              - iso2
+            Exclude:
+              - test.rb
+            Include:
+              - another_test.rb
+        YAML
+      end
+
+      it 'merges array parameters with parent or default configuration' do
+        examples_configuration = configuration_from_file['Naming/VariableNumber']
+        expect(examples_configuration['Exclude'].map { |abs_path| File.basename(abs_path) })
+          .to contain_exactly('foo.rb', 'test.rb')
+        expect(examples_configuration['Include']).to contain_exactly('bar.rb', 'another_test.rb')
+        expect(examples_configuration['AllowedIdentifiers'])
+          .to contain_exactly(*%w[capture3 iso8601 rfc1123_date rfc2822 rfc3339 rfc822 iso2])
+      end
+    end
+
     context 'when a department is disabled', :restore_registry do
       let(:file_path) { '.rubocop.yml' }