[PR c++/78469] default ctor makes dtor required

[Nathan Sidwell <nathan at acm dot org>]

Jason,
I've figured out what's happening here.  Just not sure of the most 
prudent way to fix it.

struct no_destr {
  no_destr() = default;

protected:
  ~no_destr() = default;
};

void *Foo ()
{
  return new no_destr ();
}

no_destr is a type for which the default ctor is not DECL_ARTIFICIAL, 
but is_trivial is true.  type_build_ctor_call returns true because of that.

After parsing 'no_destr ()' part of the new expr, we're inside 
build_new_1, which because it's an explicit_value_init, we end up doing:
  	      /* Something like `new int()'.  */
	      tree val = build_value_init (type, complain);

build_value_init ends up in build_over_call at:
 else if (!DECL_DELETED_FN (fn)
	   && trivial_fn_p (fn))
    {
      ...
      else if (default_ctor_p (fn))
	{
	  if (is_dummy_object (argarray[0]))
	    return force_target_expr (DECL_CONTEXT (fn), void_node, complain);

and force_target_expr ends up (via build_target_expr) with trying to 
build a clean up for the object.  Poof!

We need to tell that force_target_expr to not create a cleanup. Choices are
1) augment tf_subst flags to add such a flag. (somewhat icky, but simple)
2) a new force_target_expr_nocleanup routine, wrapping things appropriately.

thoughts?

nathan
--
Nathan Sidwell