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

From: Rene Rivera (grafikrobot_at_[hidden])
Date: 2007-06-07 14:59:40

K. Noel Belcourt wrote:
> 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?

AFAIK, it should be adding an empty list as the argument. As opposed to 
adding a list with the one output element. So instead of:

     lol_add(frame->args, list_new(L0, ""));

It would be:

     lol_add(frame->args, L0);

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