Re: [PATCH] c++: improve class NTTP object pretty printing [PR111471]

[Jason Merrill <jason@redhat.com>]

On 9/19/23 12:40, Patrick Palka wrote:
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk/13?

OK for trunk.  What's your argument for backporting?

> -- >8 --
> 
> 1. Move class NTTP object pretty printing to a more general spot in
>     the pretty printer.
> 2. Print the type of an class NTTP object alongside its CONSTRUCTOR
>     value, like dump_expr would have done.
> 3. Don't pretty print const VIEW_CONVERT_EXPR wrapping class NTTPs.
> 
> 	PR c++/111471
> 
> gcc/cp/ChangeLog:
> 
> 	* cxx-pretty-print.cc (cxx_pretty_printer::expression)
> 	<case VAR_DECL>: Print the value of a class NTTP object.
> 	<case VIEW_CONVERT_EXPR>: Strip cosnt VIEW_CONVERT_EXPR
> 	wrappers for class NTTPs.
> 	(pp_cxx_template_argument_list): Don't handle the class
> 	NTTP objects here.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/concepts/diagnostic19.C: New test.
> ---
>   gcc/cp/cxx-pretty-print.cc                   | 19 +++++++++++++++++--
>   gcc/testsuite/g++.dg/concepts/diagnostic19.C | 20 ++++++++++++++++++++
>   2 files changed, 37 insertions(+), 2 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/concepts/diagnostic19.C
> 
> diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc
> index 909a9dc917f..7cd43151592 100644
> --- a/gcc/cp/cxx-pretty-print.cc
> +++ b/gcc/cp/cxx-pretty-print.cc
> @@ -1121,6 +1121,15 @@ cxx_pretty_printer::expression (tree t)
>         t = OVL_FIRST (t);
>         /* FALLTHRU */
>       case VAR_DECL:
> +      if (DECL_NTTP_OBJECT_P (t))
> +	{
> +	  /* Print the type followed by the CONSTRUCTOR value of an
> +	     NTTP object.  */
> +	  simple_type_specifier (cv_unqualified (TREE_TYPE (t)));
> +	  expression (DECL_INITIAL (t));
> +	  break;
> +	}
> +      /* FALLTHRU */
>       case PARM_DECL:
>       case FIELD_DECL:
>       case CONST_DECL:
> @@ -1261,6 +1270,14 @@ cxx_pretty_printer::expression (tree t)
>         pp_cxx_right_paren (this);
>         break;
>   
> +    case VIEW_CONVERT_EXPR:
> +      if (TREE_CODE (TREE_OPERAND (t, 0)) == TEMPLATE_PARM_INDEX)
> +	{
> +	  /* Strip const VIEW_CONVERT_EXPR wrappers for class NTTPs.  */
> +	  expression (TREE_OPERAND (t, 0));
> +	  break;
> +	}
> +      /* FALLTHRU */
>       default:
>         c_pretty_printer::expression (t);
>         break;
> @@ -1966,8 +1983,6 @@ pp_cxx_template_argument_list (cxx_pretty_printer *pp, tree t)
>   	  if (TYPE_P (arg) || (TREE_CODE (arg) == TEMPLATE_DECL
>   			       && TYPE_P (DECL_TEMPLATE_RESULT (arg))))
>   	    pp->type_id (arg);
> -	  else if (VAR_P (arg) && DECL_NTTP_OBJECT_P (arg))
> -	    pp->expression (DECL_INITIAL (arg));
>   	  else
>   	    pp->expression (arg);
>   	}
> diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic19.C b/gcc/testsuite/g++.dg/concepts/diagnostic19.C
> new file mode 100644
> index 00000000000..20cdb63380b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/concepts/diagnostic19.C
> @@ -0,0 +1,20 @@
> +// Verify our pretty printing of class NTTP objects.
> +// PR c++/111471
> +// { dg-do compile { target c++20 } }
> +
> +struct A { bool value; };
> +
> +template<A V>
> +  requires (V.value) // { dg-message {'\(V\).value \[with V = A\{false\}\]'} }
> +void f();
> +
> +template<A V> struct B { static constexpr auto value = V.value; };
> +
> +template<class T>
> +  requires T::value // { dg-message {'T::value \[with T = B<A\{false\}>\]'} }
> +void g();
> +
> +int main() {
> +  f<A{false}>(); // { dg-error "no match" }
> +  g<B<A{false}>>(); // { dg-error "no match" }
> +}