directly exclude InputParameter types to avoid self-referencing DataFrame_Impl, which doesn't play well with older gcc, probably clang either

Author: Enchufa2

inst/include/Rcpp/DataFrame.h

@@ -47,13 +47,12 @@ namespace Rcpp{
             set__(other) ;
         }
 
-        // enabled only when T doesn't already provide its own conversion
-        // so this doesn't compete with that conversion, while still accepting
-        // anything wrap()-able, including third-party types (e.g. arma::mat)
-        template <typename T,
-                  typename std::enable_if<
-                      !std::is_convertible<T, DataFrame_Impl<StoragePolicy>>::value,
-                  int>::type = 0>
+        // enabled for everything except the InputParameter family (which
+        // each offer their own operator T() conversion), so this doesn't
+        // compete with that conversion, while still accepting anything
+        // wrap()-able, including third-party types (e.g. arma::mat)
+        template <typename T, typename std::enable_if<
+            !traits::is_input_parameter<T>::value, int>::type = 0>
         DataFrame_Impl( const T& obj ) ;
 
         DataFrame_Impl& operator=( DataFrame_Impl& other){

inst/include/Rcpp/InputParameter.h

@@ -2,7 +2,8 @@
 //
 // InputParameter.h: Rcpp R/C++ interface class library --
 //
-// Copyright (C) 2013    Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2013 - 2025 Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2026        Dirk Eddelbuettel, Romain Francois and Iñaki Ucar
 //
 // This file is part of Rcpp.
 //
@@ -94,6 +95,21 @@ namespace Rcpp {
         struct input_parameter<const T&> {
             typedef typename Rcpp::ConstReferenceInputParameter<T> type ;
         } ;
+
+        // detects the InputParameter family, which each offer their own
+        // operator T() converting to whatever type they wrap. Generic
+        // wrap()-based converting constructors (e.g. DataFrame_Impl) use this
+        // to exclude these types, so that they don't compete with them
+        template <typename T>
+        struct is_input_parameter : false_type {};
+        template <typename T>
+        struct is_input_parameter<InputParameter<T>> : true_type {};
+        template <typename T>
+        struct is_input_parameter<ReferenceInputParameter<T>> : true_type {};
+        template <typename T>
+        struct is_input_parameter<ConstInputParameter<T>> : true_type {};
+        template <typename T>
+        struct is_input_parameter<ConstReferenceInputParameter<T>> : true_type {};
     }
 
 }

inst/include/Rcpp/api/meat/DataFrame.h

@@ -22,10 +22,8 @@
 namespace Rcpp{
 
      template <template <class> class StoragePolicy>
-     template <class T,
-               typename std::enable_if<
-                   !std::is_convertible<T, DataFrame_Impl<StoragePolicy> >::value,
-               int>::type>
+     template <class T, typename std::enable_if<
+         !traits::is_input_parameter<T>::value, int>::type>
      DataFrame_Impl<StoragePolicy>::DataFrame_Impl( const T& obj){
         set__(Shield<SEXP>(wrap(obj)));
      }