Re: [PATCH/RFA] Introduce new $_isvoid() convenience function

[Eli Zaretskii <eliz@gnu.org>]

> From: Sergio Durigan Junior <sergiodj@redhat.com>
> Cc: dje@google.com, gdb-patches@sourceware.org
> Date: Fri, 13 Sep 2013 14:44:53 -0300
> 
> > And now a question about this feature: what will use of this function
> > do in versions of GDB before 7.7?
> 
> I am not sure I understood your question.  Do you want to know what will
> happen when the user calls a non-existent $_isvoid convenience function?

Yes.

>   Starting program: /home/sergio/work/src/git/isvoid/build-64/a.out 
> 
>   Temporary breakpoint 1, main () at 1.c:12
>   12          return 0;
>   (gdb) p $_isvoid ($var)
>   Invalid data type for function to be called.

Exactly.  That's a confusing diagnostics.  Do we care?  Can we do
anything about it?

>   (gdb) p $_isvoid (a)
>   Invalid data type for function to be called.
>   (gdb) p $_isvoid (1)
>   Invalid data type for function to be called.
> 
> Is this what you wanted to know?  IOW, the user won't be able to call
> this function from inside his/her script on a GDB prior to 7.7.
> 
> Thanks,
> 
> -- 
> Sergio
> 
> gdb/
> 2013-09-13  Sergio Durigan Junior  <sergiodj@redhat.com>
> 
> 	* NEWS: Mention new convenience function $_isvoid.
> 	* value.c (isvoid_internal_fn): New function.
> 	(_initialize_values): Add new convenience function $_isvoid.
> 
> gdb/doc/
> 2013-09-13  Sergio Durigan Junior  <sergiodj@redhat.com>
> 
> 	* gdb.texinfo (Convenience Functions): Mention new convenience
> 	function $_isvoid.
> 
> gdb/testsuite/
> 2013-09-13  Sergio Durigan Junior  <sergiodj@redhat.com>
> 
> 	* gdb.base/gdbvars.c (foo_void): New function.
> 	(foo_int): Likewise.
> 	* gdb.base/gdbvars.exp (test_convenience_functions): New
> 	function.  Call it.
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index ad97f6f..35aaf41 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -3,6 +3,11 @@
>  
>  *** Changes since GDB 7.6
>  
> +* New convenience function "$_isvoid", to check whether an expression
> +  is void.  A void expression is an expression where the type of the
> +  result is `void'; for example, when calling a function whose return
> +  type is `void'.

But this function is being introduced mainly for testing convenience
variables, isn't it?  Then the explanation should describe that use
case first, I think.

> +@item $_isvoid (@var{expr})
> +@findex $_isvoid@r{, convenience function}
> +Return one if the expression @var{expr} is void.  Otherwise it
> +returns zero.
> +
> +A void expression is an expression where the type of the result is
> +`void'.  For example, given the following function:
> +
> +@smallexample
> +void
> +foo (void)
> +@{
> +@}
> +@end smallexample
> +
> +The result of calling it inside @value{GDBN} is `void':
> +
> +@smallexample
> +(@value{GDBP}) print foo ()
> +$1 = void
> +(@value{GDBP}) print $_isvoid (foo ())
> +$2 = 1
> +(@value{GDBP}) set $v = foo ()
> +(@value{GDBP}) print $v
> +$3 = void
> +(@value{GDBP}) print $_isvoid ($v)
> +$4 = 1
> +@end smallexample
> +
> +@end table

This is fine, but I would also include an example with $_exitcode.

Thanks.