Resolve inherit_from correctly without namespace (rubocop#3421)

The current implementation of `load_file` will load the hash from a
config, then apply the base_configs to that hash, before converting it
to a proper `Config` object.

This can clobber inherited configuration since merging will happen in
resolve_inheritance, but will just keep the keys from both and then when
`add_missing_namespaces` is called, one will be dropped.

Since `Config` inherits from `Hash`, there shouldn't be a problem with
doing the `resolve_*` methods after the `config = Config.new` line since
all the normal Hash methods are available (.delete specifically).

CHANGELOG.md

@@ -23,6 +23,7 @@
 * [#3380](https://github.com/bbatsov/rubocop/issues/3380): Fix false positive in `Style/TrailingUnderscoreVariable` cop. ([@drenmi][])
 * [#3388](https://github.com/bbatsov/rubocop/issues/3388): Fix bug where `Lint/ShadowedException` would register an offense when rescuing different numbers of custom exceptions in multiple rescue groups. ([@rrosenblum][])
 * [#3386](https://github.com/bbatsov/rubocop/issues/3386): Make `VariableForce` understand an empty RegExp literal as LHS to `=~`. ([@drenmi][])
+* [#3421](https://github.com/bbatsov/rubocop/pull/3421): Fix clobbering `inherit_from` additions when not using Namespaces in the configs. ([@nicklamuro][])
 
 ### Changes
 
@@ -2328,3 +2329,4 @@
 [@metcalf]: https://github.com/metcalf
 [@annaswims]: https://github.com/annaswims
 [@soutaro]: https://github.com/soutaro
+[@nicklamuro]: https://github.com/nicklamuro

lib/rubocop/config_loader.rb

@@ -33,19 +33,20 @@ def clear_options
       def load_file(path)
         path = File.absolute_path(path)
         hash = load_yaml_configuration(path)
-
-        resolve_inheritance_from_gems(hash, hash.delete('inherit_gem'))
-        resolve_inheritance(path, hash)
-        resolve_requires(path, hash)
-
-        hash.delete('inherit_from')
         config = Config.new(hash, path)
 
         config.deprecation_check do |deprecation_message|
           warn("#{path} - #{deprecation_message}")
         end
 
         config.add_missing_namespaces
+
+        resolve_inheritance_from_gems(config, config.delete('inherit_gem'))
+        resolve_inheritance(path, config)
+        resolve_requires(path, config)
+
+        config.delete('inherit_from')
+
         config.validate
         config.make_excludes_absolute
         config

spec/rubocop/config_loader_spec.rb

@@ -252,6 +252,44 @@
       end
     end
 
+    context 'when a file inherits and overrides with non-namedspaced cops' do
+      let(:file_path) { '.rubocop.yml' }
+
+      before do
+        create_file('example.rb', '')
+
+        create_file('line_length.yml',
+                    ['LineLength:',
+                     '  Max: 120'])
+
+        create_file(file_path,
+                    ['inherit_from:',
+                     '  - line_length.yml',
+                     '',
+                     'LineLength:',
+                     '  AllowHeredoc: false'])
+      end
+
+      it 'returns includes both of the cop changes' do
+        config =
+          default_config.merge(
+            'Metrics/LineLength' => {
+              'Description' =>
+              default_config['Metrics/LineLength']['Description'],
+              'StyleGuide' =>
+              'https://github.com/bbatsov/ruby-style-guide#80-character-limits',
+              'Enabled' => true,
+              'Max' => 120,             # overridden in line_length.yml
+              'AllowHeredoc' => false,  # overridden in rubocop.yml
+              'AllowURI' => true,
+              'URISchemes' => %w(http https)
+            }
+          )
+
+        expect(configuration_from_file).to eq(config)
+      end
+    end
+
     context 'when a file inherits from an expanded path' do
       let(:file_path) { '.rubocop.yml' }