Re: [PATCH] c++: decltype of by-ref capture proxy of ref [PR115504]

[Jason Merrill <jason@redhat.com>]

On 6/24/24 21:00, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> for trunk/14?
> 
> -- >8 --
> 
> The capture proxy handling in finish_decltype_type added in r14-5330
> was stripping the reference type of a capture proxy's captured variable,
> which is desirable for a by-value capture, but not for a by-ref capture
> (of a reference).

I'm not sure why we would want it for by-value, either; regardless of 
the capture kind, decltype(x) is int&.

> 	PR c++/115504
> 
> gcc/cp/ChangeLog:
> 
> 	* semantics.cc (finish_decltype_type): For a by-reference
> 	capture proxy, don't strip the reference type (if any) of
> 	the captured variable.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp1y/decltype-auto8.C: New test.
> ---
>   gcc/cp/semantics.cc                         |  4 +++-
>   gcc/testsuite/g++.dg/cpp1y/decltype-auto8.C | 11 +++++++++++
>   2 files changed, 14 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto8.C
> 
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 08f5f245e7d..b4f626924af 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -12076,9 +12076,11 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
>   	    {
>   	      if (is_normal_capture_proxy (expr))
>   		{
> +		  bool by_ref = TYPE_REF_P (TREE_TYPE (expr));
>   		  expr = DECL_CAPTURED_VARIABLE (expr);
>   		  type = TREE_TYPE (expr);
> -		  type = non_reference (type);
> +		  if (!by_ref)
> +		    type = non_reference (type);
>   		}
>   	      else
>   		{
> diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto8.C b/gcc/testsuite/g++.dg/cpp1y/decltype-auto8.C
> new file mode 100644
> index 00000000000..9a5e435f14f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto8.C
> @@ -0,0 +1,11 @@
> +// PR c++/115504
> +// { dg-do compile { target c++14 } }
> +
> +void f(int& x) {
> +  [&x]() {
> +    decltype(auto) a = x;
> +    using type = decltype(x);
> +    using type = decltype(a);
> +    using type = int&; // not 'int'
> +  };
> +}