[Fix #12667] Avoid loading excluded configuration

This change fixes an error that can occur when file names are
given explicitly on the command line together with
`--force-exclusion`.

In order to check if the given files are to be excluded, we
must load configuration. The problem is that `.rubocop.yml`
files in directories with excluded files (e.g. a `vendor`
directory) might contain directives that will cause RuboCop
to crash, such as `require` with an extension that's not
available.

What saves us in this situation is that we don't need to
load configuration for the file as such. We can load
configuration for the current directory instead. The reason
is that `Exclude` parameters on the top level are not
shadowed by `Exclude` in other `.rubocop.yml` files in
subdirectories, as documented here:

https://docs.rubocop.org/rubocop/1.60/configuration.html#include-and-exclude-are-relative-to-their-directory

The `--ignore-parent-exclusion` flag, if given, changes the
situation and we must load the most adjacent `.rubocop.yml`
file.

changelog/fix_loading_of_excluded_config.md

@@ -0,0 +1 @@
+* [#12667](https://github.com/rubocop/rubocop/issues/12667): Don't load excluded configuration. ([@jonas054][])

lib/rubocop/target_finder.rb

@@ -16,6 +16,10 @@ def force_exclusion?
       @options[:force_exclusion]
     end
 
+    def ignore_parent_exclusion?
+      @options[:ignore_parent_exclusion]
+    end
+
     def debug?
       @options[:debug]
     end
@@ -181,7 +185,7 @@ def included_file?(file)
       ruby_file?(file) || configured_include?(file)
     end
 
-    def process_explicit_path(path, mode)
+    def process_explicit_path(path, mode) # rubocop:disable Metrics/CyclomaticComplexity
       files = path.include?('*') ? Dir[path] : [path]
 
       if mode == :only_recognized_file_types || force_exclusion?
@@ -191,7 +195,11 @@ def process_explicit_path(path, mode)
       return files unless force_exclusion?
 
       files.reject do |file|
-        config = @config_store.for(file)
+        # When --ignore-parent-exclusion is given, we must look at the configuration associated with
+        # the file, but in the default case when --ignore-parent-exclusion is not given, can safely
+        # look only at the configuration for the current directory, since it's only the Exclude
+        # parameters we're going to check.
+        config = @config_store.for(ignore_parent_exclusion? ? file : '.')
         config.file_to_exclude?(file)
       end
     end

spec/rubocop/target_finder_spec.rb

@@ -62,8 +62,15 @@
   subject(:target_finder) { described_class.new(config_store, options) }
 
   let(:config_store) { RuboCop::ConfigStore.new }
-  let(:options) { { force_exclusion: force_exclusion, debug: debug } }
+  let(:options) do
+    {
+      force_exclusion: force_exclusion,
+      ignore_parent_exclusion: ignore_parent_exclusion,
+      debug: debug
+    }
+  end
   let(:force_exclusion) { false }
+  let(:ignore_parent_exclusion) { false }
   let(:debug) { false }
 
   before do
@@ -144,8 +151,26 @@
       context "when it's forced to adhere file exclusion configuration" do
         let(:force_exclusion) { true }
 
-        it 'excludes them' do
-          expect(found_basenames).to eq(['ruby2.rb'])
+        context 'when parent exclusion is in effect' do
+          before do
+            create_file('dir2/.rubocop.yml', <<~YAML)
+              require:
+                - unloadable_extension
+            YAML
+          end
+
+          it 'excludes only files that are excluded on top level and does not load ' \
+             'other configuration files unnecessarily' do
+            expect(found_basenames).to eq(['ruby2.rb', 'executable'])
+          end
+        end
+
+        context 'when parent exclusion is ignored' do
+          let(:ignore_parent_exclusion) { true }
+
+          it 'excludes files that are excluded on any level' do
+            expect(found_basenames).to eq(['ruby2.rb'])
+          end
         end
       end
     end