[Boost-build] [Boost][build] Passing empty argument to rule

From: K. Noel Belcourt (kbelco_at_[hidden])
Date: 2007-06-07 14:52:59

Hi,

I've got a rule like this :

rule dart-run ( target sources * : status : user : system : command :  
output + )
{
        ECHO "output = $(output)" ;
}

and I want to know how to setup the frame arguments so the output  
(7th argument) evaluates to empty, and the output echo is  
suppressed.  Here's the code (in make1.c) where I setup to evaluate  
the rule.

LIST* initial_args = list_copy( L0, dart_rule->next );
FRAME frame[1];
frame_init( frame );

lol_add( frame->args, list_new( initial_args, target->name ) );
append_int_string(frame->args, status);
append_double_string(frame->args, time->user);
append_double_string(frame->args, time->system);
lol_add(frame->args, list_new(L0, newstr(executed_command)));

if (!command_output)
        lol_add(frame->args, list_new(L0, ""));
else
        lol_add(frame->args, list_new(L0, newstr(command_output)));

if( lol_get( frame->args, 2 ) )
     evaluate_rule( dart_rule->string, frame );

As you can see, when the 7th argument is null, I create an "" string,  
which doesn't evaluate to the empty string in the dart-run rule.  Any  
ideas on how to setup the frame argument so that when command_output  
is null, the rule is correctly called?

Thanks.

-- Noel