On Wed, Jun 27, 2018 at 12:53 PM, Marek Polacek <pola...@redhat.com> wrote:
> This PR complains about us accepting invalid code like
>
> template<unsigned int> struct A {};
> A<-1> a;
>
> Where we should detect the narrowing: [temp.arg.nontype] says
> "A template-argument for a non-type template-parameter shall be a converted
> constant expression ([expr.const]) of the type of the template-parameter."
> and a converted constant expression can contain only
> - integral conversions other than narrowing conversions,
> - [...]."
> It spurred e.g.
> <https://stackoverflow.com/questions/28184888/how-implicit-conversion-works-for-non-type-template-parameters>
> and has >=3 dups so it has some visibility.
>
> I think build_converted_constant_expr needs to set check_narrowing.
> check_narrowing also always mentions that it's in { } but that is no longer
> true; in the future it will also apply to <=>. We'd probably have to add a
> new
> flag to struct conversion if wanted to distinguish between these.
>
> This does not yet fix detecting narrowing in function templates (78244).
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-06-27 Marek Polacek <pola...@redhat.com>
>
> PR c++/57891
> * call.c (build_converted_constant_expr): Set check_narrowing.
> * decl.c (compute_array_index_type): Add warning sentinel. Use
> input_location.
> * pt.c (convert_nontype_argument): Return NULL_TREE if any errors
> were reported.
> * typeck2.c (check_narrowing): Don't mention { } in diagnostic.
>
> * g++.dg/cpp0x/Wnarrowing6.C: New test.
> * g++.dg/cpp0x/Wnarrowing7.C: New test.
> * g++.dg/cpp0x/Wnarrowing8.C: New test.
> * g++.dg/cpp0x/constexpr-data2.C: Add dg-error.
> * g++.dg/init/new43.C: Adjust dg-error.
> * g++.dg/other/fold1.C: Likewise.
> * g++.dg/parse/array-size2.C: Likewise.
> * g++.dg/other/vrp1.C: Add dg-error.
> * g++.dg/template/char1.C: Likewise.
> * g++.dg/ext/builtin12.C: Likewise.
> * g++.dg/template/dependent-name3.C: Adjust dg-error.
>
> diff --git gcc/cp/call.c gcc/cp/call.c
> index 209c1fd2f0e..956c7b149dc 100644
> --- gcc/cp/call.c
> +++ gcc/cp/call.c
> @@ -4152,7 +4152,10 @@ build_converted_constant_expr (tree type, tree expr,
> tsubst_flags_t complain)
> }
>
> if (conv)
> - expr = convert_like (conv, expr, complain);
> + {
> + conv->check_narrowing = !processing_template_decl;
Why !processing_template_decl? This needs a comment.
> + expr = convert_like (conv, expr, complain);
> + }
> else
> expr = error_mark_node;
>
> diff --git gcc/cp/pt.c gcc/cp/pt.c
> index 3780f3492aa..12d1a1e1cd3 100644
> --- gcc/cp/pt.c
> +++ gcc/cp/pt.c
> @@ -6669,9 +6669,10 @@ convert_nontype_argument (tree type, tree expr,
> tsubst_flags_t complain)
> /* C++17: A template-argument for a non-type template-parameter
> shall
> be a converted constant expression (8.20) of the type of the
> template-parameter. */
> + int errs = errorcount;
> expr = build_converted_constant_expr (type, expr, complain);
> if (expr == error_mark_node)
> - return error_mark_node;
> + return errorcount > errs ? NULL_TREE : error_mark_node;
I suspect that what you want here is to check (complain & tf_error)
rather than errorcount. Otherwise it needs a comment.
Jason
