Re: [Boost-build] Need Help with generators

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2005-11-06 04:59:09

Schnyder Franz wrote:
> Everything worked fine when I used lib or exe.
> Then I needed to set a special flag for only one source file. I used the 
> obj rule and run in to a problem: "error: Ambiguity found when searching 
> for best transformation".
> 
> Or are my generators totally wrong and should be written in a different 
> way ?

> generators.register-composing vxworks.lst : OBJ STATIC_LIB : LST
>                                            : <toolset>vxworks ;

this is: STATIC_LIB OBJ --> LST
try:
   generators.register-composing vxworks.lst : LST : OBJ STATIC_LIB
                                             : <toolset>vxworks ;
   # LST --> STATIC_LIB OBJ

> generators.register-standard vxworks.munch : LST : C : <toolset>vxworks ;

this is: LST --> C
try:
   generators.register-standard vxworks.munch : LST : C : <toolset>vxworks ;
   # C --> LST

Trimming to the relevant parts of the output from --debug-generators...

>       trying generator vxworks.compile.c++ ( CPP -> OBJ )
>         is viable
>       trying generator vxworks.compile.c ( C -> OBJ )
>         is viable
>       ***  2  viable generators
>         generator vxworks.compile.c++
>         SUCCESS:  { vxworks%vxworks.compile.c++-BSysListenerMock.obj.OBJ 
> { ../src/BSysListenerMock.cpp.CPP } }
>         generator vxworks.compile.c
>           *** construct C
>               from { ../src/BSysListenerMock.cpp.CPP }
>           trying type C
>           trying generator vxworks.munch ( LST -> C )
>             is viable
>             generator vxworks.munch
>               *** construct LST
>                   from { ../src/BSysListenerMock.cpp.CPP }
>               trying type LST
>               trying generator vxworks.lst ( OBJ STATIC_LIB -> LST )
>                 is viable
                   ^^^^^^^^^ Here is your problem
>               ***  1  viable generators
>                 generator vxworks.lst
>                   *** construct OBJ
>                       from { ../src/BSysListenerMock.cpp.CPP }
>                   ***  1  viable generators
>                     generator vxworks.compile.c++
>                     generator vxworks.compile.c++  spawned
>                   *** construct STATIC_LIB
>                       from { ../src/BSysListenerMock.cpp.CPP }
>                   trying generator vxworks.archive ( OBJ -> STATIC_LIB )
>                     is viable
>                     generator vxworks.archive
>                     generator vxworks.archive  spawned
>                 generator vxworks.lst  spawned
>             generator vxworks.munch  spawned
>         generator vxworks.compile.c  spawned
>         { vxworks%vxworks.compile.c-BSysListenerMock.obj.OBJ { 
> vxworks%vxworks.munch-BSysListenerMock.c.C { 
> vxworks%vxworks.lst-BSysListenerMock.lst.LST { 
> vxworks%vxworks.compile.c++-BSysListenerMock.obj.OBJ { 
> ../src/BSysListenerMock.cpp.CPP } } } } }

> error: Ambiguity found when searching for best transformation

The ambiguity is that it is trying to generate an LST file from an OBJ 
file and is getting confused (CPP -> OBJ -> LST -> C -> OBJ).

What you want is CPP -> LST -> OBJ and C -> LST -> OBJ, correct? When 
compiling a C file with VxWorks, I'm assuming you don't need to "munch" 
it. If so, why don't you have C -> OBJ as normal, and

    CPP -> C -> OBJ
        ^^ munch here

then you could do the munching in the vxworks.c++ action only. This 
would remove the need for an LST intermediary. Or am I missing something?

- Reece