Fix for ClassCastException inside Struct#initialize when delegating ... via prepended module

Author: evaniainbrooks

core/src/main/java/org/jruby/RubyStruct.java

@@ -534,8 +534,8 @@ public IRubyObject initialize(ThreadContext context) {
     public IRubyObject initialize(ThreadContext context, IRubyObject arg0) {
         boolean keywords = hasNonemptyKeywords(ThreadContext.resetCallInfo(context));
 
-        if (keywords) {
-            return setupStructValuesFromHash(context, (RubyHash) arg0);
+        if (keywords && arg0 instanceof RubyHash hash) {
+            return setupStructValuesFromHash(context, hash);
         } else if (RubyStruct.getInternalVariable(context, classOf(), KEYWORD_INIT_VAR).isTrue()) {
             if (!(arg0 instanceof RubyHash hash)) throw argumentError(context, 1, 0);
             return setupStructValuesFromHash(context, hash);

spec/ruby/core/struct/initialize_spec.rb

@@ -59,4 +59,16 @@
     data.version.should == "3.2"
     data.platform.should == "OS"
   end
+
+  it "can be called via delegated ... from a prepended module" do
+    wrapper = Module.new do
+      def initialize(...)
+        super(...)
+      end
+    end
+
+    klass = Class.new(Struct.new(:a)) { prepend wrapper }
+    s = klass.new("x")
+    s.a.should == "x"
+  end
 end