Preserve generic type overrides in Sorbet casts

Assisted-By: devx/eb25d669-b4ee-4e28-9b69-129b45e1e178

Author: KaanOzkan

lib/tapioca/internal.rb

@@ -12,6 +12,7 @@
 require "tapioca/sorbet_ext/backcompat_patches"
 require "tapioca/sorbet_ext/name_patch"
 require "tapioca/sorbet_ext/generic_name_patch"
+require "tapioca/sorbet_ext/generic_type_patch"
 require "tapioca/sorbet_ext/proc_bind_patch"
 require "tapioca/sorbet_ext/void_patch"
 require "tapioca/runtime/generic_type_registry"

lib/tapioca/sorbet_ext/generic_name_patch.rb

@@ -82,26 +82,6 @@ def name
       prepend GenericPatch
     end
   end
-
-  module Utils
-    module Private
-      module PrivateCoercePatch
-        def coerce_and_check_module_types(val, check_val, check_module_type)
-          if val.is_a?(Tapioca::TypeVariableModule)
-            val.coerce_to_type_variable
-          elsif val.respond_to?(:__tapioca_override_type)
-            val.__tapioca_override_type
-          else
-            super
-          end
-        end
-      end
-
-      class << self
-        prepend(PrivateCoercePatch)
-      end
-    end
-  end
 end
 
 module Tapioca

lib/tapioca/sorbet_ext/generic_type_patch.rb

@@ -0,0 +1,48 @@
+# typed: true
+# frozen_string_literal: true
+
+module T
+  module Utils
+    module Private
+      # Preserve Tapioca's generic type variables and instantiated generic
+      # names when Sorbet coerces them into runtime types.
+      module TapiocaGenericTypeCoercePatch
+        def coerce_and_check_module_types(val, check_val, check_module_type)
+          if val.is_a?(Tapioca::TypeVariableModule)
+            val.coerce_to_type_variable
+          elsif val.respond_to?(:__tapioca_override_type)
+            val.__tapioca_override_type
+          else
+            super
+          end
+        end
+      end
+
+      class << self
+        prepend(TapiocaGenericTypeCoercePatch)
+      end
+    end
+  end
+
+  module Private
+    module Casts
+      module TapiocaGenericTypeCastPatch
+        # https://github.com/sorbet/sorbet/commit/b8d64c7fd9a08e2b9159b5d592bc2de6d586b44a
+        # inlines the Module fast path in `T.let`, `T.cast`, `T.bind`, and
+        # `T.assert_type!`, so generic module clones can reach this cast path
+        # without going through `T::Utils::Private::TapiocaGenericTypeCoercePatch`.
+        def cast(value, type, cast_method)
+          if type.respond_to?(:__tapioca_override_type)
+            type = type.__tapioca_override_type
+          end
+
+          super(value, type, cast_method)
+        end
+      end
+
+      class << self
+        prepend(TapiocaGenericTypeCastPatch)
+      end
+    end
+  end
+end

spec/tapioca/runtime/generic_type_registry_spec.rb

@@ -58,6 +58,10 @@ class GenericTypeRegistrySpec < Minitest::Spec
         end
 
         describe ".register_type" do
+          it "allows generic interface implementations to be cast to generic interface types" do
+            T.let(SampleGenericInterfaceImplementation.new, SampleGenericInterface[Object])
+          end
+
           it "does not reuse generic instances for redefined constants with the same name" do
             first_constant, first_generic_type = register_reloadable_generic
 
@@ -107,6 +111,22 @@ class SampleGenericClass
         Element = type_member
       end
 
+      module SampleGenericInterface
+        extend T::Generic
+
+        interface!
+
+        Element = type_member
+      end
+
+      class SampleGenericInterfaceImplementation
+        extend T::Generic
+
+        include SampleGenericInterface
+
+        Element = type_member
+      end
+
       class RaisesInInheritedCallback
         extend T::Generic