Add new InternalAffairs/ProcessedSourceBufferName cop

Follow up rubocop/rubocop-minitest#217 (comment).

This PR adds new `InternalAffairs/ProcessedSourceBufferName` cop.
It enforces the use of `processed_source.file_path` instead of `processed_source.buffer.name`.

```ruby
# bad
processed_source.buffer.name

# good
processed_source.file_path
```

lib/rubocop/cop/internal_affairs.rb

@@ -15,6 +15,7 @@
 require_relative 'internal_affairs/node_type_predicate'
 require_relative 'internal_affairs/numblock_handler'
 require_relative 'internal_affairs/offense_location_keyword'
+require_relative 'internal_affairs/processed_source_buffer_name'
 require_relative 'internal_affairs/redundant_context_config_parameter'
 require_relative 'internal_affairs/redundant_described_class_as_subject'
 require_relative 'internal_affairs/redundant_let_rubocop_config_new'

lib/rubocop/cop/internal_affairs/processed_source_buffer_name.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module InternalAffairs
+      # Enforces the use of `processed_source.file_path` instead of `processed_source.buffer.name`.
+      #
+      # @example
+      #
+      #   # bad
+      #   processed_source.buffer.name
+      #
+      #   # good
+      #   processed_source.file_path
+      #
+      class ProcessedSourceBufferName < Base
+        extend AutoCorrector
+
+        MSG = 'Use `file_path` instead.'
+
+        RESTRICT_ON_SEND = %i[name].freeze
+
+        # @!method processed_source_buffer_name?(node)
+        def_node_matcher :processed_source_buffer_name?, <<~PATTERN
+          (send
+            (send
+              {(lvar :processed_source) (send nil? :processed_source)} :buffer) :name)
+        PATTERN
+
+        def on_send(node)
+          return unless processed_source_buffer_name?(node)
+
+          offense_range = node.children.first.loc.selector.begin.join(node.loc.expression.end)
+
+          add_offense(offense_range) do |corrector|
+            corrector.replace(offense_range, 'file_path')
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/team.rb

@@ -130,7 +130,7 @@ def autocorrect(processed_source, report, original:, offset:)
           # holds source read in from stdin, when --stdin option is used
           @options[:stdin] = new_source
         else
-          filename = processed_source.buffer.name
+          filename = processed_source.file_path
           File.write(filename, new_source)
         end
         @updated_source_file = true

spec/rubocop/cop/internal_affairs/processed_source_buffer_name_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::InternalAffairs::ProcessedSourceBufferName, :config do
+  it 'registers an offense and corrects when using `processed_source.buffer.name` and `processed_source` is a method call' do
+    expect_offense(<<~RUBY)
+      processed_source.buffer.name
+                       ^^^^^^^^^^^ Use `file_path` instead.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      processed_source.file_path
+    RUBY
+  end
+
+  it 'registers an offense and corrects when using `processed_source.buffer.name` and `processed_source` is a variable' do
+    expect_offense(<<~RUBY)
+      processed_source = create_processed_source
+      processed_source.buffer.name
+                       ^^^^^^^^^^^ Use `file_path` instead.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      processed_source = create_processed_source
+      processed_source.file_path
+    RUBY
+  end
+
+  it 'does not register an offense when using `processed_source.file_path`' do
+    expect_no_offenses(<<~RUBY)
+      processed_source.file_path
+    RUBY
+  end
+end