[Fix #10921] Fix an error when processing configuration file

Fixes #10921.

This PR fixes an error when ERB pre-processing of the configuration file.

changelog/fix_an_error_when_using_erb_in_confi.md

@@ -0,0 +1 @@
+* [#10921](https://github.com/rubocop/rubocop/issues/10921): Fix an error when ERB pre-processing of the configuration file. ([@koic][])

lib/rubocop/server/cache.rb

@@ -62,17 +62,18 @@ def cache_root_dir_from_config
             # `RuboCop::ConfigStore` has heavy dependencies, this is a lightweight implementation
             # so that only the necessary `CacheRootDirectory` can be obtained.
             require 'yaml'
-
             config_path = ConfigFinder.find_config_path(Dir.pwd)
 
-            # Ruby 3.1+
-            config_yaml = if Gem::Version.new(Psych::VERSION) >= Gem::Version.new('4.0.0')
-                            YAML.safe_load_file(config_path, permitted_classes: [Regexp, Symbol])
-                          else
-                            config = YAML.load_file(config_path)
+            require 'erb'
+            file_contents = File.read(config_path)
+            yaml_code = ERB.new(file_contents).result
+
+            config_yaml = YAML.safe_load(yaml_code, permitted_classes: [Regexp, Symbol])
 
-                            config == false ? nil : config
-                          end
+            # For compatibility with Ruby 3.0 or lower.
+            if Gem::Version.new(Psych::VERSION) < Gem::Version.new('4.0.0')
+              config_yaml == false ? nil : config_yaml
+            end
 
             config_yaml&.dig('AllCops', 'CacheRootDirectory')
           end

spec/rubocop/server/cache_spec.rb

@@ -219,5 +219,26 @@
         end
       end
     end
+
+    context 'when ERB pre-processing of the configuration file', :isolated_environment do
+      context 'when cache root path is not specified path' do
+        before do
+          cache_class.cache_root_path = nil
+        end
+
+        it 'does not raise an error' do
+          create_file('.rubocop.yml', <<~YAML)
+            Style/Encoding:
+              Enabled: <%= 1 == 1 %>
+              Exclude:
+              <% Dir['*.rb'].sort.each do |name| %>
+                - <%= name %>
+              <% end %>
+          YAML
+
+          expect { cache_class.cache_path }.not_to raise_error
+        end
+      end
+    end
   end
 end