[gdb/cli] Handle pending ^C after rl_callback_read_char for readline 7

  In commit faf01aee1d0 ("[gdb] Handle pending ^C after rl_callback_read_char")
we handled a problem (described in detail in that commit) for readline >= 8
using public readline functions rl_pending_signal and rl_check_signals.

For readline 7 (note that we require at least readline 7 so there's no need to
worry about readline 6), there was no fix though, because rl_check_signals was
not available.

Fix this by instead using the private readline function _rl_signal_handler.

There is precedent for using private readline variables and functions, but
it's something we want to get rid of (PR build/10723).  Nevertheless, I think
we can allow this specific instance because it's not used when building
against readline >= 8.

[ In the meanwhile, a fix was committed in the devel branch of the readline
repo, contained in commit 8d0c439 ("rollup of changes since readline-8.2"),
first proposed here (
https://lists.gnu.org/archive/html/bug-readline/2022-10/msg00008.html ). ]

Tested on x86_64-linux, against system readline 7.0 on openSUSE Leap 15.4.

PR cli/27813
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27813
---
 gdb/event-top.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)


base-commit: 014a602b86f08de96fc80ef3f96a87db6cccad56
  

On 5/24/23 12:41, Tom de Vries via Gdb-patches wrote:
> In commit faf01aee1d0 ("[gdb] Handle pending ^C after rl_callback_read_char")
> we handled a problem (described in detail in that commit) for readline >= 8
> using public readline functions rl_pending_signal and rl_check_signals.
> 
> For readline 7 (note that we require at least readline 7 so there's no need to
> worry about readline 6), there was no fix though, because rl_check_signals was
> not available.
> 
> Fix this by instead using the private readline function _rl_signal_handler.
> 
> There is precedent for using private readline variables and functions, but
> it's something we want to get rid of (PR build/10723).  Nevertheless, I think
> we can allow this specific instance because it's not used when building
> against readline >= 8.
> 
> [ In the meanwhile, a fix was committed in the devel branch of the readline
> repo, contained in commit 8d0c439 ("rollup of changes since readline-8.2"),
> first proposed here (
> https://lists.gnu.org/archive/html/bug-readline/2022-10/msg00008.html ). ]
> 

Committed.

Thanks,
- Tom


> Tested on x86_64-linux, against system readline 7.0 on openSUSE Leap 15.4.
> 
> PR cli/27813
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27813
> ---
>   gdb/event-top.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/event-top.c b/gdb/event-top.c
> index 193ea5363ff..005ef4b7054 100644
> --- a/gdb/event-top.c
> +++ b/gdb/event-top.c
> @@ -137,6 +137,9 @@ static struct async_signal_handler *async_sigterm_token;
>      character is processed.  */
>   void (*after_char_processing_hook) (void);
>   
> +#if RL_VERSION_MAJOR == 7
> +EXTERN_C void _rl_signal_handler (int);
> +#endif
>   
>   /* Wrapper function for calling into the readline library.  This takes
>      care of a couple things:
> @@ -203,8 +206,14 @@ gdb_rl_callback_read_char_wrapper_noexcept () noexcept
>   	   pending signal.  I'm not sure if that's possible, but it seems
>   	   better to handle the scenario than to assert.  */
>   	rl_check_signals ();
> +#elif RL_VERSION_MAJOR == 7
> +      /* Unfortunately, rl_check_signals is not available.  Use private
> +	 function _rl_signal_handler instead.  */
> +
> +      while (rl_pending_signal () != 0)
> +	_rl_signal_handler (rl_pending_signal ());
>   #else
> -      /* Unfortunately, rl_check_signals is not available.  */
> +#error "Readline major version >= 7 expected"
>   #endif
>         if (after_char_processing_hook)
>   	(*after_char_processing_hook) ();
> 
> base-commit: 014a602b86f08de96fc80ef3f96a87db6cccad56