[PATCH] c++: DR 1722: Make lambda to function pointer conv noexcept [PR90583]

[Jason Merrill]

On 9/21/20 3:57 PM, Marek Polacek wrote:
> DR 1722 clarifies that the conversion function from lambda to pointer to
> function should be noexcept(true).
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> gcc/cp/ChangeLog:
> 
> 	PR c++/90583
> 	DR 1722
> 	* lambda.c (maybe_add_lambda_conv_op): Mark the conversion function
> 	as noexcept.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/90583
> 	DR 1722
> 	* g++.dg/cpp0x/lambda/lambda-conv14.C: New test.
> ---
>   gcc/cp/lambda.c                                   |  2 ++
>   gcc/testsuite/g++.dg/cpp0x/lambda/lambda-conv14.C | 10 ++++++++++
>   2 files changed, 12 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-conv14.C
> 
> diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c
> index c94fe8edb8e..c34d68d3da3 100644
> --- a/gcc/cp/lambda.c
> +++ b/gcc/cp/lambda.c
> @@ -1189,6 +1189,8 @@ maybe_add_lambda_conv_op (tree type)
>     tree name = make_conv_op_name (rettype);
>     tree thistype = cp_build_qualified_type (type, TYPE_QUAL_CONST);
>     tree fntype = build_method_type_directly (thistype, rettype, void_list_node);
> +  /* DR 1722: The conversion function should be noexcept.  */
> +  fntype = build_exception_variant (fntype, noexcept_true_spec);
>     tree convfn = build_lang_decl (FUNCTION_DECL, name, fntype);
>     SET_DECL_LANGUAGE (convfn, lang_cplusplus);
>     tree fn = convfn;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-conv14.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-conv14.C
> new file mode 100644
> index 00000000000..869e0d51d2b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-conv14.C
> @@ -0,0 +1,10 @@
> +// PR c++/90583
> +// DR 1722: Lambda to function pointer conversion should be noexcept.
> +// { dg-do compile { target c++11 } }
> +
> +void
> +foo ()
> +{
> +  auto l = [](int){ return 42; };
> +  static_assert(noexcept((int (*)(int))(l)), "");
> +}
> 
> base-commit: b0c990f2661a2979c68c840781847efe27a0779b
>