Re: [PATCH] c++: Add -Wexceptions warning option [PR97675]

[David Malcolm <dmalcolm@redhat.com>]

On Thu, 2020-11-05 at 11:03 -0500, Marek Polacek via Gcc-patches wrote:
> This PR asks that we add a warning option for an existing (very old)
> warning, so that it can be disabled selectively.  clang++ uses
> -Wexceptions for this, so I added this new option rather than using
> e.g. -Wnoexcept.
> 
> gcc/c-family/ChangeLog:
> 
> 	PR c++/97675
> 	* c.opt (Wexceptions): New option.
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/97675
> 	* except.c (check_handlers_1): Use OPT_Wexceptions for the
> 	warning.  Use inform for the second part of the warning.
> 
> gcc/ChangeLog:
> 
> 	PR c++/97675
> 	* doc/invoke.texi: Document -Wexceptions.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/97675
> 	* g++.old-deja/g++.eh/catch10.C: Adjust dg-warning.
> 	* g++.dg/warn/Wexceptions1.C: New test.
> 	* g++.dg/warn/Wexceptions2.C: New test.
> ---
>  gcc/c-family/c.opt                          |  4 ++++
>  gcc/cp/except.c                             |  9 ++++-----
>  gcc/doc/invoke.texi                         |  8 +++++++-
>  gcc/testsuite/g++.dg/warn/Wexceptions1.C    |  9 +++++++++
>  gcc/testsuite/g++.dg/warn/Wexceptions2.C    | 10 ++++++++++
>  gcc/testsuite/g++.old-deja/g++.eh/catch10.C |  4 ++--
>  6 files changed, 36 insertions(+), 8 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/warn/Wexceptions1.C
>  create mode 100644 gcc/testsuite/g++.dg/warn/Wexceptions2.C
> 
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 426636be839..9493acb82ff 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -579,6 +579,10 @@ Werror-implicit-function-declaration
>  C ObjC RejectNegative Warning Alias(Werror=, implicit-function-
> declaration)
>  This switch is deprecated; use -Werror=implicit-function-declaration 
> instead.
>  
> +Wexceptions
> +C++ ObjC++ Var(warn_exceptions) Init(1)
> +Warn when an exception handler is shadowed by another handler.
> +
>  Wextra
>  C ObjC C++ ObjC++ Warning
>  ; in common.opt
> diff --git a/gcc/cp/except.c b/gcc/cp/except.c
> index cb1a4105dae..985206f6a64 100644
> --- a/gcc/cp/except.c
> +++ b/gcc/cp/except.c
> @@ -975,11 +975,10 @@ check_handlers_1 (tree master,
> tree_stmt_iterator i)
>        tree handler = tsi_stmt (i);
>        if (TREE_TYPE (handler) && can_convert_eh (type, TREE_TYPE
> (handler)))
>  	{

Can you add an auto_diagnostic_group here please.

> -	  warning_at (EXPR_LOCATION (handler), 0,
> -		      "exception of type %qT will be caught",
> -		      TREE_TYPE (handler));
> -	  warning_at (EXPR_LOCATION (master), 0,
> -		      "   by earlier handler for %qT", type);
> +	  if (warning_at (EXPR_LOCATION (handler), OPT_Wexceptions,
> +			  "exception of type %qT will be caught by
> earlier "
> +			  "handler", TREE_TYPE (handler)))
> +	    inform (EXPR_LOCATION (master), "for type %qT", type);
>  	  break;
>  	}
>      }

Thanks
Dave