Re: [Boost-build] Suppressing Variant Directories

From: Jonathan Biggar (jon_at_[hidden])
Date: 2008-07-26 14:10:54

Jurko Gospodnetić wrote:
>> I would like to have a flat directory structure:
>>
>> .../build/*.*
>>
>> as opposed to
>>
>> .../build/debug/threading-multi/*.*
> 
>    I do not believe this is the wanted behaviour for Boost Build based 
> builds so I do not think there is an easy way to achieve this. The only 
> thing that pops to mind is hacking Boost Build's functionality for 
> constructing the target folder name, but I really do not see the point.
> 
>    If you do not separate different build variants... you forfeit most 
> Boost Build features... E.g. no multiple-variant builds (debug/release) 
> and you have to clean the build results before building a different variant.
> 
>    Having different variants split over multiple folders should not 
> present problems... you should rarely if ever need to manually locate 
> intermediate results stored there. Use the install rule to move final 
> products into specific external folders.

In general, I agree with you, but there are specific cases where this 
causes problems.  For example, the project I'm working on generated C++ 
header files that need to be installed.  If the header file gets 
generated four times for debug/release and multi-/single-threaded 
variants, which one should be installed if I want to install all four 
variant libraries?

I've worked up a patch that does the trick for me.  It defines a new 
feature "<ignore-feature>", which allows the user to specify other 
features that should be dropped from the target's properties just before 
  the target's construct rule gets called.

I use it like this:

make foo.hpp
     : $(sources)
     : @make-foo
     : <ignore-feature>variant
       <ignore-feature>toolset
       <ignore-feature>threading
     ;

actions make-foo
{
     make-foo.sh $(>)
}

If a composite feature is ignored, then all component features of the 
composite feature are ignored too.

Comments appreciated.

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

==== tools/build/v2/build/property-set.jam#2 (text) ====

@@ -442,3 +442,25 @@
     }
     return $(.empty) ;
 }
+
+rule remove-ignored ( orig-properties )
+{
+    local to-ignore = [ $(orig-properties).get <ignore-feature> ] ;
+
+    to-ignore = <$(to-ignore)> ;
+
+    local ignored ;
+    local props = [ $(orig-properties).raw ] ;
+
+    for local prop in $(props)
+    {
+        if $(prop:G) in $(to-ignore)
+        {
+            ignored += $(prop) ;
+        }
+    }
+
+    local to-remove = [ feature.expand $(ignored) ] ;
+
+    return [ property-set.create [ set.difference $(props) : $(to-remove) ] ] ;
+}

==== tools/build/v2/build/targets.jam#2 (text) ====

@@ -1189,6 +1189,8 @@
                     $(usage-requirements) ] ;
                 usage-requirements = [ property-set.create $(usage-requirements) ] ;
 
+                rproperties = [ property-set.remove-ignored $(rproperties) ] ;
+
                 if [ modules.peek : .debug-building ]
                 {
                     ECHO [ targets.indent ]

==== tools/build/v2/tools/builtin.jam#2 (text) ====

@@ -260,6 +260,10 @@
 
 feature.feature variant : : implicit composite propagated symmetric ;
 
+# A meta-feature that tells the build system to ignore certain other features
+# when building a target
+
+feature.feature ignore-feature : : incidental free ;
 
 # Declares a new variant.
 #