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

From: Jonathan Biggar (jon_at_[hidden])
Date: 2008-07-19 21:08:12

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.

-- 
Jon Biggar
Floorboard Software
jon_at_[hidden]
jon_at_[hidden]

==== //depot/orb_main/corba/tools/build/v2/tools/generate.jam#1 - /home/corvette/jon/work/corba/tools/build/v2/tools/generate.jam ====
@@ -44,24 +44,35 @@
         local result ;
         local gr = [ $(property-set).get <generating-rule> ] ;
 
-        # FIXME: this is copy-paste from virtual-target.jam. Must
-        # have n utilty rule to call a rule like this.
-        local rule-name = [ MATCH ^@(.*) : $(gr) ] ;
-        if $(rule-name)
+        if ($gr)
         {
-            if $(tag[2])
+            # FIXME: this is copy-paste from virtual-target.jam. Must
+            # have n utilty rule to call a rule like this.
+            local rule-name = [ MATCH ^@(.*) : $(gr) ] ;
+            if $(rule-name)
+            {
+                if $(gr[2])
+                {
+                    errors.error "<generating-rule>@rulename is present but is not the only <generating-rule> feature" ;
+                }
+
+                result = [ indirect.call $(rule-name) $(self.project) $(name)
+                    : $(property-set) : $(sources) ] ;
+            }
+            else
             {
-                errors.error "<tag>@rulename is present but is not the only <tag> feature" ;
+                result = [ indirect.call $(gr) $(self.project) $(name) : $(property-set) : $(sources) ] ;
             }
 
-            result = [ indirect.call $(rule-name) $(self.project) $(name)
-                : $(property-set) : $(sources) ] ;
-
             if ! $(result)
             {
                 ECHO "warning: Unable to construct" [ full-name ] ;
             }
         }
+        else
+        {
+            errors.error "no <generating-rule> specified" ;
+        }
 
         local ur ;
         local targets ;