Re: [PATCH] c++: Fix pretty printing of function pointer type [PR98767]

[Jason Merrill <jason@redhat.com>]

On 4/16/21 6:58 PM, Patrick Palka wrote:
> When pretty printing a function pointer type via
> pp_cxx_parameter_declaration_clause, we end up always printing an empty
> parameter list because the loop that's supposed to print the parameter
> list iterates over 'args' instead of 'types', and 'args' is empty in
> this case when a FUNCTION_TYPE is passed to this routine (as opposed
> to a FUNCTION_DECL).
> 
> This patch fixes this by making the loop iterator over 'types' instead.
> This patch also moves the retrofitted PARM_DECL printing from this
> routine to pp_cxx_requires_expr, the only caller that uses it.  This
> simplification lets us easily output the trailing '...' in the parameter
> list of a variadic function, which this patch also implements.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?

OK.

> gcc/cp/ChangeLog:
> 
> 	PR c++/98767
> 	* cxx-pretty-print.c (pp_cxx_parameter_declaration_clause): Fix
> 	loop over parameter list to iterate over 'types' instead of
> 	'args'.  Output the trailing '...' for a variadic function.
> 	Remove PARM_DECL support.
> 	(pp_cxx_requires_expr): Pretty print the parameter list directly
> 	instead of going through pp_cxx_parameter_declaration_clause.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/98767
> 	* g++.dg/concepts/diagnostic16.C: New test.
> ---
>   gcc/cp/cxx-pretty-print.c                    | 48 ++++++++++++--------
>   gcc/testsuite/g++.dg/concepts/diagnostic16.C | 17 +++++++
>   2 files changed, 46 insertions(+), 19 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/concepts/diagnostic16.C
> 
> diff --git a/gcc/cp/cxx-pretty-print.c b/gcc/cp/cxx-pretty-print.c
> index a22eea5239c..894472e26e0 100644
> --- a/gcc/cp/cxx-pretty-print.c
> +++ b/gcc/cp/cxx-pretty-print.c
> @@ -1537,34 +1537,27 @@ pp_cxx_parameter_declaration (cxx_pretty_printer *pp, tree t)
>   static void
>   pp_cxx_parameter_declaration_clause (cxx_pretty_printer *pp, tree t)
>   {
> -  tree args;
> -  tree types;
> -  bool abstract;
> -
> -  // For a requires clause or the explicit printing of a parameter list
> -  // we expect T to be a chain of PARM_DECLs. Otherwise, the list of
> -  // args and types are taken from the function decl T.
> -  if (TREE_CODE (t) == PARM_DECL)
> +  gcc_assert (FUNC_OR_METHOD_TYPE_P (t) || TREE_CODE (t) == FUNCTION_DECL);
> +  tree types, args;
> +  if (TYPE_P (t))
>       {
> -      args = t;
> -      types = t;
> -      abstract = false;
> +      types = TYPE_ARG_TYPES (t);
> +      args = NULL_TREE;
>       }
>     else
>       {
> -      bool type_p = TYPE_P (t);
> -      args = type_p ? NULL : FUNCTION_FIRST_USER_PARM (t);
> -      types = type_p ? TYPE_ARG_TYPES (t) : FUNCTION_FIRST_USER_PARMTYPE (t);
> -      abstract = args == NULL || pp->flags & pp_c_flag_abstract;
> +      types = FUNCTION_FIRST_USER_PARMTYPE (t);
> +      args = FUNCTION_FIRST_USER_PARM (t);
>       }
> -  bool first = true;
> +  bool abstract = !args || (pp->flags & pp_c_flag_abstract);
>   
>     /* Skip artificial parameter for non-static member functions.  */
>     if (TREE_CODE (t) == METHOD_TYPE)
>       types = TREE_CHAIN (types);
>   
> +  bool first = true;
>     pp_cxx_left_paren (pp);
> -  for (; args; args = TREE_CHAIN (args), types = TREE_CHAIN (types))
> +  for (; types && types != void_list_node; types = TREE_CHAIN (types))
>       {
>         if (!first)
>   	pp_cxx_separate_with (pp, ',');
> @@ -1577,6 +1570,14 @@ pp_cxx_parameter_declaration_clause (cxx_pretty_printer *pp, tree t)
>   	  pp_cxx_whitespace (pp);
>   	  pp->assignment_expression (TREE_PURPOSE (types));
>   	}
> +      if (!abstract)
> +	args = TREE_CHAIN (args);
> +    }
> +  if (!types)
> +    {
> +      if (!first)
> +	pp_cxx_separate_with (pp, ',');
> +      pp_cxx_ws_string (pp, "...");
>       }
>     pp_cxx_right_paren (pp);
>   }
> @@ -2775,9 +2776,18 @@ void
>   pp_cxx_requires_expr (cxx_pretty_printer *pp, tree t)
>   {
>     pp_string (pp, "requires");
> -  if (tree parms = TREE_OPERAND (t, 0))
> +  if (tree parms = REQUIRES_EXPR_PARMS (t))
>       {
> -      pp_cxx_parameter_declaration_clause (pp, parms);
> +      bool first = true;
> +      pp_cxx_left_paren (pp);
> +      for (; parms; parms = TREE_CHAIN (parms))
> +	{
> +	  if (!first)
> +	    pp_cxx_separate_with (pp, ',' );
> +	  first = false;
> +	  pp_cxx_parameter_declaration (pp, parms);
> +	}
> +      pp_cxx_right_paren (pp);
>         pp_cxx_whitespace (pp);
>       }
>     pp_cxx_requirement_body (pp, TREE_OPERAND (t, 1));
> diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic16.C b/gcc/testsuite/g++.dg/concepts/diagnostic16.C
> new file mode 100644
> index 00000000000..49d5733faea
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/concepts/diagnostic16.C
> @@ -0,0 +1,17 @@
> +// PR c++/98767
> +// { dg-do compile { target c++20 } }
> +
> +template <typename Function, typename... Args>
> +concept Callable = requires(Function func, Args... args) { func(args...); };
> +
> +static_assert(Callable<int(*)(), bool>); // { dg-error "failed" }
> +// { dg-message {Function = int \(\*\)\(\)} "" { target *-*-* } 5 }
> +
> +static_assert(Callable<char(*)(int*), bool>); // { dg-error "failed" }
> +// { dg-message {Function = char \(\*\)\(int\*\)} "" { target *-*-* } 5 }
> +
> +static_assert(Callable<short(*)(int*, int), bool>); // { dg-error "failed" }
> +// { dg-message {Function = short int \(\*\)\(int\*, int\)} "" { target *-*-* } 5 }
> +
> +static_assert(Callable<long(*)(int*, int, ...), bool>); // { dg-error "failed" }
> +// { dg-message {Function = long int \(\*\)\(int\*, int, \.\.\.\)} "" { target *-*-* } 5 }
>