run the module body only once per dll

Author: kevinushey

ChangeLog

@@ -41,6 +41,14 @@
 	* inst/tinytest/cpp/Module.cpp: Add a class deriving from another
 	* inst/tinytest/test_module.R: Test the new checks
 
+2026-10-29  Kevin Ushey <kevinushey@gmail.com>
+
+	* inst/include/Rcpp/Module.h (RCPP_MODULE): Run the module body only the
+	first time the boot function is called, since it adds to the static
+	module and every Module() call boots the module again, which duplicated
+	constructors and methods (#1527)
+	* inst/tinytest/test_module.R: Test loading a module repeatedly
+
 2026-10-29  Kevin Ushey <kevinushey@gmail.com>
 
 	* inst/include/Rcpp/Module.h (RCPP_MODULE): Wrap the module boot

inst/include/Rcpp/Module.h

@@ -637,17 +637,23 @@ namespace Rcpp {
 #define RCPP_MODULE_BOOT(name) _rcpp_module_boot_##name
 
 // the boot function is called from R via .Call(), so exceptions thrown by
-// the module body must be turned into R errors
-#define RCPP_MODULE(name)                                                         \
-    void _rcpp_module_##name##_init() ;                                           \
-    static Rcpp::Module _rcpp_module_##name( # name ) ;                           \
-    extern "C" SEXP _rcpp_module_boot_##name(){                                   \
-        BEGIN_RCPP                                                                \
-        Rcpp::internal::ModuleScope _rcpp_module_scope( & _rcpp_module_##name ) ; \
-        _rcpp_module_##name##_init( ) ;                                           \
-        return Rcpp::XPtr<Rcpp::Module>( & _rcpp_module_##name , false ) ;       \
-        END_RCPP                                                                  \
-    }                                                                             \
+// the module body must be turned into R errors; it runs every time the
+// module is loaded, but the body adds to the static module, so it may only
+// run once
+#define RCPP_MODULE(name)                                                             \
+    void _rcpp_module_##name##_init() ;                                               \
+    static Rcpp::Module _rcpp_module_##name( # name ) ;                               \
+    static bool _rcpp_module_##name##_initialized = false ;                           \
+    extern "C" SEXP _rcpp_module_boot_##name(){                                       \
+        BEGIN_RCPP                                                                    \
+        if( ! _rcpp_module_##name##_initialized ){                                    \
+            Rcpp::internal::ModuleScope _rcpp_module_scope( & _rcpp_module_##name ) ; \
+            _rcpp_module_##name##_init( ) ;                                           \
+            _rcpp_module_##name##_initialized = true ;                                \
+        }                                                                             \
+        return Rcpp::XPtr<Rcpp::Module>( & _rcpp_module_##name , false ) ;           \
+        END_RCPP                                                                      \
+    }                                                                                 \
     void _rcpp_module_##name##_init()
 
 // silly little dance to suppress a 'defined but not used variable' warning

inst/tinytest/test_module.R

@@ -189,3 +189,13 @@ expect_identical( res, c(1, 2, 3) )
 ## rather than an error (which used to surface at garbage collection)
 r <- new( ModuleRandomizer )
 expect_identical( r$finalize(), NULL )
+
+## loading a module again must not re-run its body, which used to add
+## every constructor and method to the static module once more (#1527);
+## this redefines the module's classes, so it comes last
+is_demo_module <- function(dll) is.loaded("_rcpp_module_boot_demoModule", PACKAGE = dll[["name"]])
+dll <- Filter(is_demo_module, getLoadedDLLs())[[1L]]
+mod <- Module( "demoModule", PACKAGE = dll, mustStart = TRUE )
+mod <- Module( "demoModule", PACKAGE = dll, mustStart = TRUE )
+expect_equal( length( mod$ModuleWorld@constructors ), 1L )
+expect_equal( length( mod$ModuleWorld@methods$greet@nargs ), 1L )