From 8fb17176cb6b9f1ac7580f359379764da60d3d0b Mon Sep 17 00:00:00 2001
From: Alexander Momchilov <alexander.momchilov@shopify.com>
Date: Fri, 21 Aug 2026 09:47:49 -0400
Subject: [PATCH] Raise for abstract class methods

They're not yet tested, and the implementation is broken (missing `extend TypeToolkit::HasAbstractMethods` on the singleton class).
---
 lib/type_toolkit/dsl.rb |  4 +++-
 spec/interface_spec.rb  | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/type_toolkit/dsl.rb b/lib/type_toolkit/dsl.rb
index 7dd6d98..c346ce0 100644
--- a/lib/type_toolkit/dsl.rb
+++ b/lib/type_toolkit/dsl.rb
@@ -37,7 +37,9 @@ def abstract(method_name)
       #     # is_singleton_method = true, owner is `Foo.singleton_class`
       #     abstract def self.foo; end
       #   end
-      method_owner = is_singleton_method ? singleton_class : self #: as Module[top] & HasAbstractMethods
+      method_owner = is_singleton_method ? raise(NotImplementedError, <<~MSG) : self
+        Abstract singleton methods are not supported yet.
+      MSG
 
       # Register the fact that this method is meant to be abstract,
       # used by APIs like `abstract_method_declared?` and `Method#abstract?`
diff --git a/spec/interface_spec.rb b/spec/interface_spec.rb
index 24ddc54..c52bf23 100644
--- a/spec/interface_spec.rb
+++ b/spec/interface_spec.rb
@@ -401,5 +401,19 @@ def something_else; end
         end
       end
     end
+
+    describe "Abstract class methods" do
+      it "are not yet supported" do
+        test_context = self
+
+        Module.new do
+          interface!
+
+          test_context.assert_raises(NotImplementedError) do
+            abstract def self.abstract_class_method; end # rubocop:disable Style/ClassMethodsDefinitions
+          end
+        end
+      end
+    end
   end
 end