make finalize() a no-op for never-constructed module objects

ChangeLog

@@ -1,3 +1,12 @@
+2026-10-22  Kevin Ushey  <kevinushey@gmail.com>
+
+	* src/module.cpp (CppObject__finalize): Make finalize() a no-op for a
+	module object that was never constructed (created without arguments for a
+	class without a default constructor); it used to fail on the dummy
+	pointer, and the failure surfaced as an error message at garbage
+	collection
+	* inst/tinytest/test_module.R: Add test
+
 2026-10-22  Michael Sumner <mdsumner@gmail.com>
 
 	* R/00_classes.R: Define C++Field, C++OverloadedMethods and C++Constructor

inst/tinytest/test_module.R

@@ -123,3 +123,10 @@ gctorture(TRUE)
 res <- gadget$value()
 gctorture(FALSE)
 expect_identical( res, c(1, 2, 3) )
+
+#    test.Module.finalize.dummy <- function(){
+## an object created without arguments for a class lacking a default
+## constructor holds the dummy pointer; finalizing it must be a no-op
+## rather than an error (which used to surface at garbage collection)
+r <- new( ModuleRandomizer )
+expect_identical( r$finalize(), NULL )

src/module.cpp

@@ -108,7 +108,14 @@ RCPP_FUN_4(SEXP, CppField__set, XP_Class cl, SEXP field_xp, SEXP obj, SEXP value
     cl->setProperty(field_xp, obj, value);
     return R_NilValue;
 }
+
+extern SEXP rcpp_dummy_pointer;
+
 RCPP_FUN_2(SEXP, CppObject__finalize, XP_Class cl, SEXP obj) {
+    // an object created without arguments for a class lacking a default
+    // constructor holds the dummy pointer: there is nothing to finalize
+    if (obj == rcpp_dummy_pointer)
+        return R_NilValue;
     cl->run_finalizer(obj);
     return R_NilValue;
 }