[Boost-bugs] [Boost C++ Libraries] #4423: fix for #4400

Subject: [Boost-bugs] [Boost C++ Libraries] #4423: fix for #4400
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-07-11 09:37:21

#4423: fix for #4400
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 Reporter:  Wolf Lammen <ookami1@…>       |       Owner:  no-maintainer
     Type:  Patches                       |      Status:  new          
Milestone:  Boost 1.44.0                  |   Component:  preprocessor 
  Version:  Boost 1.44.0                  |    Severity:  Problem      
 Keywords:                                |  
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 The attached patch file fixes the bug described in ticket #4400

 Yet to be done: has somebody access to a compiler based on Edison Design
 Group C++ front end version 3.0.8 or earlier? I would like the code being
 compiled by such a compiler and see, whether the code fork for that
 compiler type runs properly.

 The preprocessor code has not been touched in the past 7 years, and
 seemingly there is no active maintainer around, so I chose to keep the
 fixes impact on existing software is minimal as possible. I can tell from
 the sources that the author of the preprocessor code meant
 BOOST_PP_SEQ_REST_N to fulfil a certain undocumented condition, which it
 violates in a single case, so a good fix would care about said condition.
 But BOOST_PP_SEQ_REST_N is much more at the core of the preprocessor, and
 a change affects more code. So, instead, I made the only client
 BOOST_PP_SEQ_REPLACE  relying on that condition when BOOST_PP_SEQ_REST_N
 fails to fulfil it, independent of BOOST_PP_SEQ_REST_N.

 The code contains a compiler fork, that treats preprocessors with
 rescanning and/or argument substitution problems differently. I used the
 same technics I found elsewhere in boost code to work around that
 problems. I think I it is ok, and my (compliant) compiler does not
 complain, but, of course, there is a slight chance I got it wrong.

 To verify the fix is correct I used a self written test suite, that checks
 the validity of a BOOST_PP_SEQ_REPLACE
 implementation. It uses a brute force method, i.e. sequences of all
 possible lengths are tested, each element is replaced, and each
 replacement is individually checked. The test suite allows for varying the
 input sequence, so sequences containing characters with special meaning to
 the preprocessor has been tested as well.
 The test suite is a UNIX bash shell script, which I attached here as well.

 The test results show without exception so far,
 - that the fixed code produces exactly the same results than the old code,
 whereever the old code succeeds. This includes the distribution of white
 space characters in between sequence elements;
 - that the fixed code produces the correct result, where the old code
 fails;
 - that the same holds if the BOOST_PP_CONFIG_EDG flag is forced. However,
 the GNU preprocessor I used is standard compliant, so an old EDG based
 compiler might still fail.

 As I changed the code in seq_replace.hpp significantly, and in a not
 trivial manner, I added my copyright notice.

 Cheers

 Wolf Lammen

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4423>
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