[C++ Patch/RFC] PR 63757

[Paolo Carlini]

Hi,

in this rejects-valid, as part of build_user_type_conversion_1, 
standard_conversion is called by implicit_conversion with a *null* expr, 
thus the condition in standard_conversion

  /* [conv.ptr]
     A null pointer constant can be converted to a pointer type; ... A
     null pointer constant of integral type can be converted to an
     rvalue of type std::nullptr_t. */
  if ((tcode == POINTER_TYPE || TYPE_PTRMEM_P (to)
       || NULLPTR_TYPE_P (to))
      && expr && null_ptr_cst_p (expr))
    conv = build_conv (ck_std, to, conv);

is false and the snippet is rejected. Should we pass a nullptr_node as 
expr in such cases, ie, when handling conversions functions returning 
std::nullptr_t?!? The below passes testing.

Thanks,
Paolo.

//////////////////////
Index: cp/call.c
===================================================================
--- cp/call.c   (revision 218022)
+++ cp/call.c   (working copy)
@@ -3685,7 +3685,8 @@ build_user_type_conversion_1 (tree totype, tree ex
          conversion *ics
            = implicit_conversion (totype,
                                   rettype,
-                                  0,
+                                  NULLPTR_TYPE_P (rettype)
+                                  ? nullptr_node : NULL_TREE,
                                   /*c_cast_p=*/false, convflags,
                                   complain);
 
Index: testsuite/g++.dg/cpp0x/nullptr33.C
===================================================================
--- testsuite/g++.dg/cpp0x/nullptr33.C  (revision 0)
+++ testsuite/g++.dg/cpp0x/nullptr33.C  (working copy)
@@ -0,0 +1,19 @@
+// PR c++/63757
+// { dg-do compile { target c++11 } }
+
+typedef decltype(nullptr) nullptr_t;
+
+void bar(void*) {}
+ 
+struct foo
+{
+  operator nullptr_t()
+  {
+    return nullptr;
+  }
+};
+
+int main()
+{
+  bar(foo());
+}