Add ForbidTEnum cop

config/default.yml

@@ -110,6 +110,13 @@ Sorbet/ForbidSuperclassConstLiteral:
   Exclude:
   - db/migrate/*.rb
 
+Sorbet/ForbidTEnum:
+  Description: 'Forbid usage of T::Enum.'
+  Enabled: false
+  VersionAdded: <<next>>
+  VersionChanged: <<next>>
+  Safe: false
+
 Sorbet/ForbidTStruct:
   Description: 'Forbid usage of T::Struct.'
   Enabled: false

lib/rubocop/cop/sorbet/forbid_t_enum.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require "rubocop"
+
+module RuboCop
+  module Cop
+    module Sorbet
+      # Disallow using `T::Enum`.
+      #
+      # @example
+      #
+      #   # bad
+      #   class MyEnum < T::Struct
+      #     enums do
+      #       A = new
+      #       B = new
+      #     end
+      #   end
+      #
+      #   # good
+      #   class MyEnum
+      #     A = "a'
+      #     B = "b"
+      #     C = "c"
+      #   end
+      class ForbidTEnum < RuboCop::Cop::Base
+        MSG = "Using `T::Enum` is deprecated."
+
+        # @!method t_enum?(node)
+        def_node_matcher(:t_enum?, <<~PATTERN)
+          (const (const {nil? cbase} :T) :Enum)
+        PATTERN
+
+        def on_class(node)
+          add_offense(node) if t_enum?(node.parent_class)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/sorbet_cops.rb

@@ -12,6 +12,7 @@
 require_relative "sorbet/forbid_untyped_struct_props"
 require_relative "sorbet/implicit_conversion_method"
 require_relative "sorbet/callback_conditionals_binding"
+require_relative "sorbet/forbid_t_enum"
 require_relative "sorbet/forbid_t_struct"
 require_relative "sorbet/forbid_t_unsafe"
 require_relative "sorbet/forbid_t_untyped"

manual/cops.md

@@ -21,6 +21,7 @@ In the following section you find all available cops:
 * [Sorbet/ForbidIncludeConstLiteral](cops_sorbet.md#sorbetforbidincludeconstliteral)
 * [Sorbet/ForbidRBIOutsideOfAllowedPaths](cops_sorbet.md#sorbetforbidrbioutsideofallowedpaths)
 * [Sorbet/ForbidSuperclassConstLiteral](cops_sorbet.md#sorbetforbidsuperclassconstliteral)
+* [Sorbet/ForbidTEnum](cops_sorbet.md#sorbetforbidtenum)
 * [Sorbet/ForbidTStruct](cops_sorbet.md#sorbetforbidtstruct)
 * [Sorbet/ForbidTUnsafe](cops_sorbet.md#sorbetforbidtunsafe)
 * [Sorbet/ForbidTUntyped](cops_sorbet.md#sorbetforbidtuntyped)

manual/cops_sorbet.md

@@ -448,6 +448,33 @@ Name | Default value | Configurable values
 --- | --- | ---
 Exclude | `db/migrate/*.rb` | Array
 
+## Sorbet/ForbidTEnum
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Disabled | No | No | <<next>> | <<next>>
+
+Disallow using `T::Enum`.
+
+### Examples
+
+```ruby
+# bad
+class MyEnum < T::Struct
+  enums do
+    A = new
+    B = new
+  end
+end
+
+# good
+class MyEnum
+  A = "a'
+  B = "b"
+  C = "c"
+end
+```
+
 ## Sorbet/ForbidTStruct
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

spec/rubocop/cop/sorbet/forbid_t_enum_spec.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe(RuboCop::Cop::Sorbet::ForbidTEnum, :config) do
+  describe("Offenses") do
+    it "adds offense when inheriting T::Enum on a multiline class" do
+      expect_offense(<<~RUBY)
+        class Foo < T::Enum
+        ^^^^^^^^^^^^^^^^^^^ Using `T::Enum` is deprecated.
+        end
+      RUBY
+    end
+
+    it "adds offense when inheriting T::Enum on a singleline class" do
+      expect_offense(<<~RUBY)
+        class Foo < T::Enum; end
+        ^^^^^^^^^^^^^^^^^^^^^^^^ Using `T::Enum` is deprecated.
+      RUBY
+    end
+
+    it "adds offense when inheriting ::T::Enum" do
+      expect_offense(<<~RUBY)
+        class Foo < ::T::Enum; end
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^ Using `T::Enum` is deprecated.
+      RUBY
+    end
+
+    it "adds offense for nested enums" do
+      expect_offense(<<~RUBY)
+        class Foo < T::Enum
+        ^^^^^^^^^^^^^^^^^^^ Using `T::Enum` is deprecated.
+          class Bar < T::Enum
+          ^^^^^^^^^^^^^^^^^^^ Using `T::Enum` is deprecated.
+          end
+        end
+      RUBY
+    end
+  end
+
+  describe("No offenses") do
+    it "does not add offense when not using T::Enum" do
+      expect_no_offenses(<<~RUBY)
+        class Foo
+        end
+
+        class Bar < Baz; end
+
+        class Baz
+          extend T::Enum
+        end
+
+        class T::Enum; end
+      RUBY
+    end
+  end
+end