Re: C++ PATCH to reject initializating flexible array members in constructors (PR c++/72775)

[Jason Merrill <jason at redhat dot com>]

If the problem is the member initializer, we can diagnose that
directly rather than wait until we're in a constructor.

On Wed, Dec 7, 2016 at 3:26 PM, Marek Polacek <polacek@redhat.com> wrote:
> We were crashing in finish_expr_stmt here:
>  676       /* If we ran into a problem, make sure we complained.  */
>  677       gcc_assert (expr != error_mark_node || seen_error ());
> Well, we ran into a problem, but never raised an error.  The problem was that
> we couldn't determine the max index of the array when default-initizalizing the
> members (at the beginning of cp_parser_ctor_initializer_opt).  Jason's
> preference seems to be to disable initialization of a flexible array member in
> a constructor and that is what this patch attempts to do.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2016-12-07  Marek Polacek  <polacek@redhat.com>
>
>         PR c++/72775
>         * init.c (perform_member_init): Diagnose initialization of a flexible
>         array member in a constructor.
>
>         * g++.dg/ext/flexary20.C: New.
>
> diff --git gcc/cp/init.c gcc/cp/init.c
> index b4b6cdb..01009c9 100644
> --- gcc/cp/init.c
> +++ gcc/cp/init.c
> @@ -800,6 +800,10 @@ perform_member_init (tree member, tree init)
>            in that case.  */
>         init = build_x_compound_expr_from_list (init, ELK_MEM_INIT,
>                                                 tf_warning_or_error);
> +      else if (TREE_CODE (type) == ARRAY_TYPE
> +              && TYPE_DOMAIN (type) == NULL_TREE)
> +       error_at (DECL_SOURCE_LOCATION (member),
> +                 "initialization of a flexible array member in a constructor");
>
>        if (init)
>         finish_expr_stmt (cp_build_modify_expr (input_location, decl,
> diff --git gcc/testsuite/g++.dg/ext/flexary20.C gcc/testsuite/g++.dg/ext/flexary20.C
> index e69de29..ff97b06 100644
> --- gcc/testsuite/g++.dg/ext/flexary20.C
> +++ gcc/testsuite/g++.dg/ext/flexary20.C
> @@ -0,0 +1,49 @@
> +// PR c++/72775
> +// { dg-do compile { target c++11 } }
> +// { dg-options -Wno-pedantic }
> +
> +struct S {
> +  int i;
> +  char a[] = "foo"; // { dg-error "initialization of a flexible array member in a constructor" }
> +  S () {}
> +};
> +
> +struct T {
> +  int i;
> +  char a[] = "foo"; // { dg-error "initialization of a flexible array member in a constructor" }
> +};
> +
> +struct U {
> +  int i;
> +  char a[] = "foo"; // { dg-error "initialization of a flexible array member in a constructor" }
> +  U ();
> +};
> +
> +U::U() {}
> +
> +int
> +main ()
> +{
> +  struct T t;
> +}
> +
> +struct V {
> +  int i;
> +  struct W {
> +    int j;
> +    char a[] = "foo"; // { dg-error "initialization of a flexible array member in a constructor" }
> +  } w;
> +  V () {}
> +};
> +
> +template <class T>
> +struct X {
> +  int i;
> +  T a[] = "foo"; // { dg-error "initialization of a flexible array member in a constructor" }
> +};
> +
> +void
> +fn ()
> +{
> +  struct X<char> x;
> +}
>
>         Marek