On Wed, 20 Sep 2023, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
... and perhaps 13?
>
> -- >8 --
>
> This fixes some missed SFINAE in grok_array_decl when checking a C++23
> multidimensional subscript operator expression.
>
> Note the existing pedwarn code paths are a backward compability fallback
> for treating invalid a[x, y, z] as a[(x, y, z)], but this should only be
> done outside of a SFINAE context I think.
>
> PR c++/111493
>
> gcc/cp/ChangeLog:
>
> * decl2.cc (grok_array_decl): Guard errors with tf_error.
> In the pedwarn code paths, return error_mark_node when in
> a SFINAE context.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp23/subscript15.C: New test.
> ---
> gcc/cp/decl2.cc | 36 +++++++++++++++---------
> gcc/testsuite/g++.dg/cpp23/subscript15.C | 24 ++++++++++++++++
> 2 files changed, 47 insertions(+), 13 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp23/subscript15.C
>
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index b402befba6d..6eb6d8c57d6 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -477,7 +477,9 @@ grok_array_decl (location_t loc, tree array_expr, tree
> index_exp,
> {
> /* If it would be valid albeit deprecated expression in
> C++20, just pedwarn on it and treat it as if wrapped
> - in (). */
> + in () unless we're in a SFINAE context. */
> + if (!(complain & tf_error))
> + return error_mark_node;
> pedwarn (loc, OPT_Wcomma_subscript,
> "top-level comma expression in array subscript "
> "changed meaning in C++23");
> @@ -487,7 +489,7 @@ grok_array_decl (location_t loc, tree array_expr, tree
> index_exp,
> = build_x_compound_expr_from_vec (orig_index_exp_list,
> NULL, complain);
> if (orig_index_exp == error_mark_node)
> - expr = error_mark_node;
> + return error_mark_node;
> release_tree_vector (orig_index_exp_list);
> }
> }
> @@ -512,22 +514,29 @@ grok_array_decl (location_t loc, tree array_expr, tree
> index_exp,
> {
> if ((*index_exp_list)->is_empty ())
> {
> - error_at (loc, "built-in subscript operator without expression "
> - "list");
> + if (complain & tf_error)
> + error_at (loc, "built-in subscript operator without expression "
> + "list");
> return error_mark_node;
> }
> tree idx = build_x_compound_expr_from_vec (*index_exp_list, NULL,
> tf_none);
> if (idx != error_mark_node)
> - /* If it would be valid albeit deprecated expression in C++20,
> - just pedwarn on it and treat it as if wrapped in (). */
> - pedwarn (loc, OPT_Wcomma_subscript,
> - "top-level comma expression in array subscript "
> - "changed meaning in C++23");
> + {
> + /* If it would be valid albeit deprecated expression in C++20,
> + just pedwarn on it and treat it as if wrapped in () unless
> + we're in a SFINAE context. */
> + if (!(complain & tf_error))
> + return error_mark_node;
> + pedwarn (loc, OPT_Wcomma_subscript,
> + "top-level comma expression in array subscript "
> + "changed meaning in C++23");
> + }
> else
> {
> - error_at (loc, "built-in subscript operator with more than one "
> - "expression in expression list");
> + if (complain & tf_error)
> + error_at (loc, "built-in subscript operator with more than one "
> + "expression in expression list");
> return error_mark_node;
> }
> index_exp = idx;
> @@ -561,8 +570,9 @@ grok_array_decl (location_t loc, tree array_expr, tree
> index_exp,
> swapped = true, array_expr = p2, index_exp = i1;
> else
> {
> - error_at (loc, "invalid types %<%T[%T]%> for array subscript",
> - type, TREE_TYPE (index_exp));
> + if (complain & tf_error)
> + error_at (loc, "invalid types %<%T[%T]%> for array subscript",
> + type, TREE_TYPE (index_exp));
> return error_mark_node;
> }
>
> diff --git a/gcc/testsuite/g++.dg/cpp23/subscript15.C
> b/gcc/testsuite/g++.dg/cpp23/subscript15.C
> new file mode 100644
> index 00000000000..1528ee71306
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp23/subscript15.C
> @@ -0,0 +1,24 @@
> +// PR c++/111493
> +// { dg-do compile { target c++23 } }
> +
> +template<class T, class... Ts>
> +concept CartesianIndexable = requires(T t, Ts... ts) { t[ts...]; };
> +
> +static_assert(!CartesianIndexable<int>);
> +static_assert(!CartesianIndexable<int, int>);
> +static_assert(!CartesianIndexable<int, int, int>);
> +
> +static_assert(!CartesianIndexable<int*>);
> +static_assert(CartesianIndexable<int*, int>);
> +static_assert(!CartesianIndexable<int*, int, int>);
> +
> +template<class... Ts>
> +struct A {
> + void operator[](Ts...);
> +};
> +
> +static_assert(!CartesianIndexable<A<>, int>);
> +static_assert(CartesianIndexable<A<int>, int>);
> +static_assert(!CartesianIndexable<A<int>>);
> +static_assert(!CartesianIndexable<A<int>, int, int>);
> +static_assert(CartesianIndexable<A<int, int>, int, int>);
> --
> 2.42.0.216.gbda494f404
>
>
