Merge pull request #101 from Shopify/uk-refine-mutable-constant

Refine `Style/MutableConstant` to process `T.let` expressions.

lib/rubocop/cop/sorbet/mutable_constant_sorbet_aware_behaviour.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "rubocop/cop/style/mutable_constant"
+
+module RuboCop
+  module Cop
+    module Sorbet
+      module MutableConstantSorbetAwareBehaviour
+        def self.prepended(base)
+          base.def_node_matcher(:t_let, <<~PATTERN)
+            (send (const nil? :T) :let $_constant _type)
+          PATTERN
+        end
+
+        def on_assignment(value)
+          t_let(value) do |constant|
+            value = constant
+          end
+
+          super(value)
+        end
+      end
+    end
+  end
+end
+
+RuboCop::Cop::Style::MutableConstant.prepend(
+  RuboCop::Cop::Sorbet::MutableConstantSorbetAwareBehaviour
+)

lib/rubocop/cop/sorbet_cops.rb

@@ -28,3 +28,5 @@
 require_relative "sorbet/sigils/strong_sigil"
 require_relative "sorbet/sigils/enforce_sigil_order"
 require_relative "sorbet/sigils/enforce_single_sigil"
+
+require_relative "sorbet/mutable_constant_sorbet_aware_behaviour"

manual/cops.md

@@ -34,3 +34,8 @@ In the following section you find all available cops:
 * [Sorbet/ValidSigil](cops_sorbet.md#sorbetvalidsigil)
 
 <!-- END_COP_LIST -->
+
+In addition to the cops defined in this gem, it also modifies the behaviour of some other cops
+defined in other RuboCop gems:
+
+* [Style/MutableConstant](https://docs.rubocop.org/rubocop/cops_style.html#stylemutableconstant): In addition to the default behaviour, RuboCop Sorbet makes this cop `T.let` aware, so that `CONST = T.let([1, 2, 3], T::Array[Integer])` is also treated as a mutable literal constant value.