Re: [Boost-build] Patch for generate.jam to generate to be wrapped by other rules

From: Eric Woodruff (eric.woodruff_at_[hidden])
Date: 2008-07-23 13:13:00

Can you explain why the indirect rule is needed? I was following your 
example to create a rule to invoke an ant script and this seemed to work 
for me an ant.jam:

rule ant ( name : script : properties * )
{
     FLAGS on $(name) += [ compute-ant-flags $(name) : $(properties) ] ;
     generate $(name) : $(script) : $(properties) 
<generating-rule>@ant.do-ant ;
}

rule do-ant ( project name : property-set : sources * )
{
     local a  = [
        new non-scanning-action $(sources) : ant.invoke : 
$(property-set) ] ;

     return [ new file-target $(name) : [ $(sources[1]).type ] : 
$(project) : $(a) ] ;
}

actions invoke
{
         ANT_HOME="$(.ant-home-dir)"
         "$(.ant-bin)" -f $(>) $(FLAGS)
}

Jonathan Biggar wrote:
> Jurko Gospodnetić wrote:
>>   Hi Jonathan.
>>
>>> The generate main target currently only works if you pass it a 
>>> <generating-rule> using the '@' construction.  If you don't, it 
>>> silently just doesn't do anything.
>>>
>>> Here's a patch that cleans this up so that it properly gives an error 
>>> if it can't run the <generating-rule>, and also just tries to call 
>>> the rule via indirect.call if no '@' prefix is found, which allows 
>>> people to write wrapper rules that use generate.
>>
>>   Thanks for the patch.
>>
>>   I'll look at it but one thing I do not understand is what you mean 
>> by 'which allows people to write weapper rules that use generate'.
> 
> The idea was to be able to write a rule 'foo' in  foo.jam file that uses 
> generate internally with the generating rule also declared in foo.jam. 
> The problem is that foo.jam isn't a project, so it can't use the '@' 
> syntax to specify a rule.
> 
> I've attached an example tarball that demonstrates what the patch allows 
> me to do.  It defines cat.jam, which allows the user to create a rule 
> that catenates multiple files into a target.  Without the patch to 
> generate.jam, the user would have to write this by hand.
> 
> I've also attached a new patch for generate.jam that fixes a typo in my 
> previous patch.
> 
>>   So far when Boost Build wants to take a 'pointer to a rule' argument 
>> it consistently requires that you prefix the rule name with a @ 
>> character. Why would this place be special and allow the user to skip 
>> the @ character?
> 
> Because the @ requires a project context, which isn't available if you 
> want to wrap generate in a .jam file.
> 
>> Also, Boost Build depends on such 'indirect' feature values begining 
>> with @ to do some processing on them in the 
>> property.translate-indirect to make sure those rules are processed in 
>> the context of the correct module.
> 
> Yes, translate-indirect recognizes '@' and translates it into an 
> indirect call.  So there's no problem if the call is already indirect, 
> since it will call the correct rule anyway.
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost-build