[Boost-bugs] [Boost C++ Libraries] #2017: leaf_node_d matches leading skip tokens

Subject: [Boost-bugs] [Boost C++ Libraries] #2017: leaf_node_d matches leading skip tokens
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-06-18 09:49:12

#2017: leaf_node_d matches leading skip tokens
-------------------------------------+--------------------------------------
 Reporter:  j.swoboda_at_[hidden]  |       Owner:  djowel 
     Type:  Bugs                     |      Status:  new    
Milestone:  Boost 1.36.0             |   Component:  spirit 
  Version:  Boost 1.35.0             |    Severity:  Problem
 Keywords:                           |  
-------------------------------------+--------------------------------------
 Since spirit 1.86 (boost 1.35.0) the match of leaf_node_d contains any
 skip tokens directly before the actual match, if there was another token
 before.

 Example:
 Add a skip parser to libs/spirit/example/fundamental/ast_calc.cpp line
 131:
   tree_parse_info<> info = ast_parse(str.c_str(), calc, ch_p('a'));
 Build and feed the program with "1+a2" (called input a) or "a1+a2" (called
 input b).

 Output:
 (a) The parse tree has a root node "+" with two child nodes "1" and "a2",
 the calculation yields "1" (due to being unable to convert "a2" to a
 number).
 (b) Results in the same parse tree as (a), that is, the leading skip token
 is in fact ignored, but not any subsequent ones.

 Expected output:
 The second child node should only contain "2". This can be achieved by
 replacing leaf_node_d with reduced_node_d in tree_calc_grammar.hpp.

 Relevance:
 This renders leaf_node_d useless in conjunction with skip parsers and
 breaks the runtime behaviour of existing grammars. Feel free to upgrade it
 to Showstopper.

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/2017>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.