Update ConfigObsoletion so that parameters can be deprecated but still accepted

changelog/change_update_configobsoletion_so_that.md

@@ -0,0 +1 @@
+* [#9100](https://github.com/rubocop-hq/rubocop/pull/9100): Update `ConfigObsoletion` so that parameters can be deprecated but still accepted. ([@dvandersluis][])

lib/rubocop/config_obsoletion.rb

@@ -104,6 +104,7 @@ class ConfigObsoletion
     OBSOLETE_COPS = Hash[*(RENAMED_COPS + MOVED_COPS + REMOVED_COPS +
                            REMOVED_COPS_WITH_REASON + SPLIT_COPS).flatten]
 
+    # Parameters can be deprecated but not disabled by setting `severity: :warning`
     OBSOLETE_PARAMETERS = [
       {
         cops: %w[Layout/SpaceAroundOperators Style/SpaceAroundOperators],
@@ -214,8 +215,11 @@ class ConfigObsoletion
       }
     ].freeze
 
+    attr_reader :warnings
+
     def initialize(config)
       @config = config
+      @warnings = []
     end
 
     def reject_obsolete_cops_and_parameters
@@ -256,9 +260,17 @@ def obsolete_enforced_style_message(cop, param, enforced_style, alternative)
     end
 
     def obsolete_parameters
-      OBSOLETE_PARAMETERS.map do |params|
-        obsolete_parameter_message(params[:cops], params[:parameters],
-                                   params[:alternative])
+      OBSOLETE_PARAMETERS.collect do |params|
+        messages = obsolete_parameter_message(params[:cops], params[:parameters],
+                                              params[:alternative])
+
+        # Warnings are collected separately and not added to the error message
+        if messages && params.fetch(:severity, :error) == :warning
+          @warnings.concat(messages)
+          next
+        end
+
+        messages
       end
     end
 

lib/rubocop/config_validator.rb

@@ -42,7 +42,7 @@ def validate
         ConfigLoader.default_configuration.key?(key)
       end
 
-      @config_obsoletion.reject_obsolete_cops_and_parameters
+      check_obsoletions
 
       alert_about_unrecognized_cops(invalid_cop_names)
       check_target_ruby
@@ -68,6 +68,13 @@ def validate_section_presence(name)
 
     attr_reader :target_ruby
 
+    def check_obsoletions
+      @config_obsoletion.reject_obsolete_cops_and_parameters
+      return unless @config_obsoletion.warnings.any?
+
+      warn Rainbow("Warning: #{@config_obsoletion.warnings.join("\n")}").yellow
+    end
+
     def check_target_ruby
       return if target_ruby.supported?