Re: [PATCH] c++: ICE with invalid structured bindings [PR107276]

[Jason Merrill <jason@redhat.com>]

On 10/21/22 19:29, Marek Polacek wrote:
> This test ICEs in C++23 because we reach the new code in do_auto_deduction:
> 
> 30468   if (cxx_dialect >= cxx23
> 30469       && context == adc_return_type
> 30470       && (!AUTO_IS_DECLTYPE (auto_node)
> 30471           || !unparenthesized_id_or_class_member_access_p (init))
> 30472       && (r = treat_lvalue_as_rvalue_p (maybe_undo_parenthesized_ref (init),
> 30473                                         /*return*/true)))
> 
> where 'init' is "VIEW_CONVERT_EXPR<<<< error >>>>(y)", and then the move
> in treat_lvalue_as_rvalue_p returns error_mark_node whereupon
> set_implicit_rvalue_p crashes.
> 
> I don't think such V_C_Es are useful so let's not create them.  But that
> won't fix the ICE so I'm checking the return value of move.  A structured
> bindings decl can have an error type, that is set in cp_finish_decomp:
> 
>   8908           TREE_TYPE (first) = error_mark_node;
> 
> therefore I think treat_lvalue_as_rvalue_p just needs to cope.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> 	PR c++/107276
> 
> gcc/cp/ChangeLog:
> 
> 	* typeck.cc (treat_lvalue_as_rvalue_p): Check the return value of move.
> 
> gcc/ChangeLog:
> 
> 	* tree.cc (maybe_wrap_with_location): Don't create a location wrapper
> 	when the type is erroneous.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/decomp4.C: New test.
> ---
>   gcc/cp/typeck.cc                     | 7 ++++++-
>   gcc/testsuite/g++.dg/cpp2a/decomp4.C | 8 ++++++++
>   gcc/tree.cc                          | 3 ++-
>   3 files changed, 16 insertions(+), 2 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/decomp4.C
> 
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index 16e7d85793d..5ca191759f6 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -10726,7 +10726,12 @@ treat_lvalue_as_rvalue_p (tree expr, bool return_p)
>     if (DECL_CONTEXT (retval) != current_function_decl)
>       return NULL_TREE;
>     if (return_p)
> -    return set_implicit_rvalue_p (move (expr));
> +    {
> +      expr = move (expr);
> +      if (expr == error_mark_node)
> +	return NULL_TREE;
> +      return set_implicit_rvalue_p (expr);
> +    }
>   
>     /* if the operand of a throw-expression is a (possibly parenthesized)
>        id-expression that names an implicitly movable entity whose scope does not
> diff --git a/gcc/testsuite/g++.dg/cpp2a/decomp4.C b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
> new file mode 100644
> index 00000000000..28b3f172b53
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
> @@ -0,0 +1,8 @@
> +// PR c++/107276
> +// { dg-do run { target c++20 } }
> +
> +auto f(auto x) {
> +  auto [y] = x; // { dg-error "cannot decompose" }
> +  return y;
> +}
> +int i = f(0);
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index 81a6ceaf181..4e5b1df4d85 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -14352,7 +14352,8 @@ maybe_wrap_with_location (tree expr, location_t loc)
>   
>     /* For now, don't add wrappers to exceptional tree nodes, to minimize
>        any impact of the wrapper nodes.  */
> -  if (EXCEPTIONAL_CLASS_P (expr))
> +  if (EXCEPTIONAL_CLASS_P (expr)
> +      || (TREE_TYPE (expr) && EXCEPTIONAL_CLASS_P (TREE_TYPE (expr))))

I think check error_operand_p instead; I don't think it makes sense to 
look for other exceptional nodes in TREE_TYPE.

Jason