Allow enabling departments when DisabledByDefault is true

When DisabledByDefault is true, only cops explicitly enabled
in user configuration are run. This should work for
departments too.

CHANGELOG.md

@@ -27,6 +27,7 @@
 * [#4268](https://github.com/bbatsov/rubocop/issues/4268): Handle end-of-line comments when autocorrecting Style/EmptyLinesAroundAccessModifier. ([@vergenzt][])
 * [#4275](https://github.com/bbatsov/rubocop/issues/4275): Prevent `Style/MethodCallWithArgsParentheses` from blowing up on `yield`. ([@drenmi][])
 * [#3969](https://github.com/bbatsov/rubocop/issues/3969): Handle multiline method call alignment for arguments to methods. ([@jonas054][])
+* [#4304](https://github.com/bbatsov/rubocop/pull/4304): Allow enabling whole departments when `DisabledByDefault` is `true`. ([@jonas054][])
 
 ## 0.48.1 (2017-04-03)
 

lib/rubocop/config_loader.rb

@@ -147,9 +147,7 @@ def merge_with_default(config, config_file)
         end
 
         if disabled_by_default
-          config = transform(config) do |params|
-            { 'Enabled' => true }.merge(params) # Set true if not set.
-          end
+          config = handle_disabled_by_default(config, default_configuration)
         end
 
         Config.new(merge(default_configuration, config), config_file)
@@ -164,6 +162,24 @@ def target_ruby_version_to_f!(hash)
 
       private
 
+      def handle_disabled_by_default(config, new_default_configuration)
+        department_config = config.to_hash.reject { |cop| cop.include?('/') }
+        department_config.each do |dept, dept_params|
+          next unless dept_params['Enabled']
+
+          new_default_configuration.each do |cop, params|
+            next unless cop.start_with?(dept + '/')
+
+            # Retain original default configuration for cops in the department.
+            params['Enabled'] = default_configuration[cop]['Enabled']
+          end
+        end
+
+        transform(config) do |params|
+          { 'Enabled' => true }.merge(params) # Set true if not set.
+        end
+      end
+
       # Returns a new hash where the parameters of the given config hash have
       # been replaced by parameters returned by the given block.
       def transform(config)

spec/rubocop/config_loader_spec.rb

@@ -539,6 +539,32 @@ def cop_enabled?(cop_class)
           cop_class = RuboCop::Cop::Layout::TrailingWhitespace
           expect(cop_enabled?(cop_class)).to be false
         end
+
+        context 'and a department is enabled' do
+          let(:config) do
+            <<-END.strip_indent
+              AllCops:
+                DisabledByDefault: true
+              Style:
+                Enabled: true
+            END
+          end
+
+          it 'enables cops in that department' do
+            cop_class = RuboCop::Cop::Style::Alias
+            expect(cop_enabled?(cop_class)).to be true
+          end
+
+          it 'disables cops in other departments' do
+            cop_class = RuboCop::Cop::Layout::AlignHash
+            expect(cop_enabled?(cop_class)).to be false
+          end
+
+          it 'keeps cops that are disabled in default configuration disabled' do
+            cop_class = RuboCop::Cop::Style::AutoResourceCleanup
+            expect(cop_enabled?(cop_class)).to be false
+          end
+        end
       end
 
       context 'when EnabledByDefault is true' do