FEATURE: Add a cop that checks for potential fabricator shorthand use (…

…#40)

In discourse/discourse#24314, @danielwaterworth introduced the ability to use #fab! with a shorthand when simply fabricating a vanilla record with the same name as the assigned let. This PR introduces a cop that highlights places where this shorthand can be used.

lib/rubocop/cop/discourse/fabricator_shorthand.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Discourse
+      # When fabricating a record without custom attributes, we can use the
+      # fabricator shorthand as long as the identifier matches the fabricator
+      # name.
+      #
+      # @example
+      #
+      # # bad
+      # fab!(:user) { Fabricate(:user) }
+      #
+      # # good
+      # fab!(:user)
+      #
+      # When using custom attributes or the identifier doesn't match, the
+      # shorthand can't be used.
+      #
+      # @example
+      #
+      # # good
+      # fab!(:user) { Fabricate(:user, trust_level: TrustLevel[0]) }
+      #
+      # # good
+      # fab!(:another_user) { Fabricate(:user) }
+      class FabricatorShorthand < Base
+        def_node_matcher :offending_fabricator?, <<-MATCHER
+          (block
+            (send nil? :fab!
+              (sym $_identifier))
+            (args)
+            (send nil? :Fabricate
+              (sym $_identifier)))
+        MATCHER
+
+        def on_block(node)
+          offending_fabricator?(node) do |identifier|
+            add_offense(node, message: message(identifier))
+          end
+        end
+
+        private
+
+        def message(identifier)
+          "Use the fabricator shorthand: `fab!(:#{identifier})`"
+        end
+      end
+    end
+  end
+end

spec/lib/rubocop/cop/fabricator_shorthand_spec.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe RuboCop::Cop::Discourse::FabricatorShorthand, :config do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+
+  it "registers an offense when not using the fabricator shorthand" do
+    expect_offense(<<~RUBY)
+      RSpec.describe "Foo" do
+        fab!(:foo) { Fabricate(:foo) }
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Discourse/FabricatorShorthand: Use the fabricator shorthand: `fab!(:foo)`
+      end
+    RUBY
+  end
+
+  it "does not register an offense when the fabricator has attributes" do
+    expect_no_offenses(<<~RUBY)
+      RSpec.describe "Foo" do
+        fab!(:foo) { Fabricate(:foo, bar: 1) }
+      end
+    RUBY
+  end
+
+  it "does not register an offense when the identifier doesn't match" do
+    expect_no_offenses(<<~RUBY)
+      RSpec.describe "Foo" do
+        fab!(:bar) { Fabricate(:foo) }
+      end
+    RUBY
+  end
+end

stree-compat.yml

@@ -22,3 +22,8 @@ AllCops:
 
 Discourse:
   Enabled: true
+
+Discourse/FabricatorShorthand:
+  Enabled: true
+  Include:
+    - 'spec/**/*_spec.rb'