From 0511f24c041f19c241e2a72b63600dc3e0f8d2cb Mon Sep 17 00:00:00 2001
From: Nick Sutterer <apotonick@gmail.com>
Date: Mon, 27 May 2024 18:28:55 +0200
Subject: [PATCH] Use `compare_by_identity` hash for the `map` in `Circuit`.
 This fixes a bug that appeared with newer Ruby versions where people would
 use `GC.verify_compaction_references` to optimize memory consumption. After
 using the compaction, the circuit map would be corrupted when a task was a
 `Method` reference, leading to the following exception. NoMethodError:
 undefined method `[]' for nil     
 /home/nick/projects/trailblazer-activity/lib/trailblazer/activity/circuit.rb:80:in
 `next_for' thanks to @tiagotex for deep-diving into Ruby to find where this
 originates from and also providing a simple solution. :wine:

---
 lib/trailblazer/activity/schema/compiler.rb |  2 +-
 test/activity_test.rb                       | 38 +++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/lib/trailblazer/activity/schema/compiler.rb b/lib/trailblazer/activity/schema/compiler.rb
index 4873719..ffa42cf 100644
--- a/lib/trailblazer/activity/schema/compiler.rb
+++ b/lib/trailblazer/activity/schema/compiler.rb
@@ -24,7 +24,7 @@ def call(intermediate, implementation, config_merge: {})
 
           # From the intermediate "template" and the actual implementation, compile a {Circuit} instance.
           def schema_components(intermediate, implementation, config)
-            wiring = {}
+            wiring = {}.compare_by_identity # https://ruby-doc.org/3.3.0/Hash.html#class-Hash-label-Modifying+an+Active+Hash+Key
             nodes_attributes  = []
 
             intermediate.wiring.each do |task_ref, outs|
diff --git a/test/activity_test.rb b/test/activity_test.rb
index 84fbc6a..6424b2d 100644
--- a/test/activity_test.rb
+++ b/test/activity_test.rb
@@ -87,3 +87,41 @@ def call(*)
     assert_equal activity.extend(call_module).call, "overridden call!"
   end
 end
+
+class GCBugTest < Minitest::Spec
+  it "still finds {.method} tasks after GC compression" do
+    intermediate = Activity::Schema::Intermediate.new(
+      {
+        Activity::Schema::Intermediate::TaskRef(:a) => [Activity::Schema::Intermediate::Out(:success, :b)],
+        Activity::Schema::Intermediate::TaskRef(:b, stop_event: true) => []
+      },
+      {:b => :success},
+      :a # start
+    )
+
+    module Step
+      extend T.def_tasks(:create)
+    end
+
+    implementation = {
+      :a => Schema::Implementation::Task(Step.method(:create), [Activity::Output(Activity::Right, :success)], []),
+      :b => Schema::Implementation::Task(Trailblazer::Activity::End.new(semantic: :success), [], []),
+    }
+
+
+    activity = Activity.new(Activity::Schema::Intermediate::Compiler.(intermediate, implementation))
+
+    assert_invoke activity, seq: %([:create])
+
+# TODO: add tests for different Rubys
+    GC.verify_compaction_references(expand_heap: true, toward: :empty)
+
+# Without the fix, this *might* throw the following exception:
+#
+# NoMethodError: undefined method `[]' for nil
+#     /home/nick/projects/trailblazer-activity/lib/trailblazer/activity/circuit.rb:80:in `next_for'
+
+    assert_invoke activity, seq: %([:create])
+  end
+
+end