Add Sorbet/Refinement

config/default.yml

@@ -1,3 +1,11 @@
+Sorbet/Refinement:
+  Description: >- 
+                  Checks for the use of Ruby Refinements library. Refinements add
+                  complexity and incur a performance penalty that can be significant
+                  for large code bases. They are also not supported by Sorbet.
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 inherit_mode:
   merge:
   - Exclude

lib/rubocop/cop/sorbet/refinement.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Sorbet
+      # Checks for the use of Ruby Refinements library. Refinements add
+      # complexity and incur a performance penalty that can be significant
+      # for large code bases. Good examples are cases of unrelated
+      # methods that happen to have the same name as these module methods.
+      #
+      # @example
+      #   # bad
+      #   module Foo
+      #     refine(Date) do
+      #     end
+      #   end
+      #
+      #   # bad
+      #   module Foo
+      #     using(Date) do
+      #     end
+      #   end
+      #
+      #   # good
+      #   module Foo
+      #     bar.refine(Date)
+      #   end
+      #
+      #   # good
+      #   module Foo
+      #     bar.using(Date)
+      #   end
+
+      class Refinement < Base
+        MSG = "Do not use Ruby Refinements library as it is not supported by Sorbet."
+        RESTRICT_ON_SEND = [:refine, :using].freeze
+
+        def on_send(node)
+          return unless node.receiver.nil?
+          return unless node.first_argument&.const_type?
+
+          if node.method?(:refine)
+            return unless node.block_node
+            return unless node.parent.parent.module_type?
+          end
+
+          add_offense(node)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/sorbet_cops.rb

@@ -16,6 +16,7 @@
 require_relative "sorbet/forbid_t_unsafe"
 require_relative "sorbet/forbid_t_untyped"
 require_relative "sorbet/redundant_extend_t_sig"
+require_relative "sorbet/refinement"
 require_relative "sorbet/type_alias_name"
 require_relative "sorbet/obsolete_strict_memoization"
 require_relative "sorbet/buggy_obsolete_strict_memoization"

manual/cops.md

@@ -33,6 +33,7 @@ In the following section you find all available cops:
 * [Sorbet/MultipleTEnumValues](cops_sorbet.md#sorbetmultipletenumvalues)
 * [Sorbet/ObsoleteStrictMemoization](cops_sorbet.md#sorbetobsoletestrictmemoization)
 * [Sorbet/RedundantExtendTSig](cops_sorbet.md#sorbetredundantextendtsig)
+* [Sorbet/Refinement](cops_sorbet.md#sorbetrefinement)
 * [Sorbet/SignatureBuildOrder](cops_sorbet.md#sorbetsignaturebuildorder)
 * [Sorbet/SingleLineRbiClassModuleDefinitions](cops_sorbet.md#sorbetsinglelinerbiclassmoduledefinitions)
 * [Sorbet/StrictSigil](cops_sorbet.md#sorbetstrictsigil)

manual/cops_sorbet.md

@@ -759,6 +759,43 @@ class Example
 end
 ```
 
+## Sorbet/Refinement
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Enabled | Yes | No | <<next>> | -
+
+Checks for the use of Ruby Refinements library. Refinements add
+complexity and incur a performance penalty that can be significant
+for large code bases. Good examples are cases of unrelated
+methods that happen to have the same name as these module methods.
+
+### Examples
+
+```ruby
+# bad
+module Foo
+  refine(Date) do
+  end
+end
+
+# bad
+module Foo
+  using(Date) do
+  end
+end
+
+# good
+module Foo
+  bar.refine(Date)
+end
+
+# good
+module Foo
+  bar.using(Date)
+end
+```
+
 ## Sorbet/SignatureBuildOrder
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

spec/rubocop/cop/sorbet/refinement_spec.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+RSpec.describe(RuboCop::Cop::Sorbet::Refinement, :config) do
+  it "reports an offense for use of using" do
+    expect_offense(<<~RUBY, "my_class.rb")
+      using MyRefinement
+      ^^^^^^^^^^^^^^^^^^ Do not use Ruby Refinements library as it is not supported by Sorbet.
+    RUBY
+  end
+
+  it "reports an offense for use of refine" do
+    expect_offense(<<~RUBY, "my_refinement.rb")
+      module MyRefinement
+        refine(String) do
+        ^^^^^^^^^^^^^^ Do not use Ruby Refinements library as it is not supported by Sorbet.
+          def to_s
+            "foo"
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offense for use of using with non-const argument" do
+    expect_no_offenses(<<~RUBY, "my_class.rb")
+      using "foo"
+    RUBY
+  end
+
+  it "reports no offense for use of refine with non-const argument" do
+    expect_no_offenses(<<~RUBY, "my_refinement.rb")
+      module MyRefinement
+        refine "foo" do
+          def to_s
+            "foo"
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offense for use of refine with no block argument" do
+    expect_no_offenses(<<~RUBY, "my_refinement.rb")
+      module MyRefinement
+        refine(String)
+      end
+    RUBY
+  end
+
+  it "reports no offense for use of refine outside of module" do
+    expect_no_offenses(<<~RUBY, "my_refinement.rb")
+      module MyNamespace
+        class MyClass
+          refine(String) do
+            def to_s
+              "foo"
+            end
+          end
+        end
+      end
+    RUBY
+  end
+end