boost_1_45_0/tools/build/v2/notes/relative_source_paths.txt

Copyright 2005 Vladimir Prus 
Distributed under the Boost Software License, Version 1.0. 
(See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) 


Hi,
recently, we had a couple of problems caused by using relative file paths, and 
I'd like to discuss what to do.

Let's use the case from CÊdric. Simplified version is:

    exe a : a.cpp dir1/qt_file.h ;
    exe b : a.cpp dir2/qt_file.h ;

Both exes have the same source cpp file but different *.h files -- which are 
processed by Qt tools. V2 currently strips directory name from all targets, 
so it tries to

   - create "bin/mvsc/debug/moc_qt_file.cpp" from dir1/qt_file.h
   - create "bin/msvc/debug/moc_qt_file.cpp" from dir2/qt_file.h

There are two solutions that I see:

   1. Rewrite the code like:
      
      lib aux : a.cpp 
      exe a : aux dir1/qt_file.h : <location-prefix>a ;
      exe b : aux dir2/qt_file.h : <location-prefix>b ;

    This way, two version of moc_qt_file.cpp will be generated to different
    places. 

  2. Rewrite the code like:

      obj a_moc : dir1/qt_file.h : <library>/qt//qt ;
      exe a : a.cpp a_moc ;
      obj b_moc : dir2/qt_file.h : <library>/qt//qt ;
      exe b : a.cpp b_moc ;

     Explicitly changing name for the problematic files.

  3. Generally change V2 so that directory part of source is preserved. This
      will generate targets:
     "bin/msvc/debug/dir1/moc_qt_file.cpp" and
     "bin/msvc/debug/dir2/moc_qt_file.cpp". No problems.

   However, there are some additional questions:

       - What if source has absolute file name?
       - What if source is "../../include/qt_file.h"?

       We can ignore directory names in those cases (i.e. use the current 
       behaviour) but that would be a bit inconsistent.

Any opinions?

Pedro Ferreira:

I think this is a corner case and BB should not try to solve everything 
automatically - otherwise it will become really complex.
I don't see a problem in requiring the user to help the build system by 
using solutions 1 or 2.
Of course, the better the error reporting, the easier it will be to 
find the cause and the cure of the problem.

TEMPLIE Cedric:

I agree with Pedro. Solution 1 or 2 is the best way to deal with this 
problem. Of course I have a preference for the solution 1, but the 
solution 2 has the advantage to work without any modification...

Toon Knapen:

I agree.