style: add custom RSpec cops

.rubocop/custom.yml

@@ -20,3 +20,9 @@ Bundler/GemComment:
 
 Style/FrozenStringLiteralComment:
   Enabled: true
+
+RSpec/Describe:
+  Enabled: true
+
+RSpec/TypeTag:
+  Enabled: true

lib/rubocop/cops.rb

@@ -1,3 +1,4 @@
 # frozen_string_literal: true
 
 require_relative "cops/lint_env"
+require_relative "cops/rspec"

lib/rubocop/cops/rspec.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+require_relative "rspec/describe"
+require_relative "rspec/type_tag"

lib/rubocop/cops/rspec/describe.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # This cops checks that top-level described is not namespaced:
+      #
+      #  # bad
+      #  RSpec.describe MyClass do
+      #    # ...
+      #  end
+      #
+      #  # good
+      #  describe MyClass do
+      #    # ...
+      #  end
+      class Describe < RuboCop::Cop::Cop
+        MSG = "Use `describe` instead of `RSpec.describe`."
+
+        def_node_matcher :rspec_describe?, <<~PATTERN
+          (send (const nil? :RSpec) :describe ...)
+        PATTERN
+
+        def on_send(node)
+          return unless rspec_describe?(node)
+          add_offense(node, location: :selector, message: MSG)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cops/rspec/type_tag.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "rubocop-rspec"
+
+module RuboCop
+  module Cop
+    module RSpec
+      # This cops checks that default `type` tag is not specified explicitly.
+      #
+      #  # bad
+      #  describe UsersController, type: :controller do
+      #    # ...
+      #  end
+      #
+      #  # good
+      #  describe UsersController do
+      #    # ...
+      #  end
+      #
+      class TypeTag < RuboCop::Cop::RSpec::Base
+        include RuboCop::Cop::RSpec::TopLevelGroup
+
+        MSG = "Avoid specifiying inferrable type tags explicitly. " \
+              "Remove `type: :%s` (it's inferred automatically)"
+
+        def_node_matcher :type_tag, <<~PATTERN
+          (pair (sym :type) (sym $_))
+        PATTERN
+
+        def on_top_level_example_group(node)
+          metadata = node.children.first.children[3]
+          return unless metadata
+
+          metadata.children.each do |arg|
+            actual_tag = type_tag(arg)
+            next unless actual_tag
+            next if actual_tag != expected_tag
+
+            break add_offense(node, message: MSG % actual_tag)
+          end
+        end
+
+        private
+
+        def expected_tag
+          file_path = processed_source.file_path
+          if file_path =~ %r{/spec/([^/]+)/}
+            Regexp.last_match[1].gsub(/s$/, "").to_sym
+          end
+        end
+      end
+    end
+  end
+end