[GCC-XML] Failure to handle __is_enum

[Brad King]

Neal Becker wrote:
> I have the current gcc_xml cvs.  It seems to choke on boost-1.37.0, where we 
> use __is_enum if gcc is 4.3. 
> 
> Running on gccxml, it seems to identify itself as gcc4.3, but it doesn't seem 
> to understand __is_enum builtin.
 >
> What's the story here?  I think gccxml is really gcc4.2, and doesn't support 
> this builtin?  In that case, how do I run gccxml and tell it to use the gcc4.2 
> config instead of gcc4.3?

gccxml uses a 4.2 parser internally.  It is non-trivial to update the 
internal version so I do it only every few versions.

We simulate the preprocessing of the target compiler including its 
system headers so that any code generation done based on the xml output 
can compile with the target compiler.  In order to handle non-standard 
code in native headers (including MSVC, Borland, and SGI) we copy them 
into a gccxml support directory and patch them.  This approach has 
worked well for years but gcc 4.3's headers use *alot* of 
compiler-specific (4.3-only) extensions.

gccxml distinguishes itself from the preprocessor of the target compiler 
by adding these definitions (documented in the man page):

  -D__GCCXML__=MMmmpp
         MM,  mm, and pp are the major, minor, and patch versions of GCC-
         XML.  This preprocessor symbol identifies GCC-XML to the  source
         code  as  it is preprocessed.  It can be used to enable GCC-XML-
         specific information.

  -D__GCCXML_GNUC__=M
         Defined to internal GCC parser major version.

  -D__GCCXML_GNUC_MINOR__=m
         Defined to internal GCC parser minor version.

  -D__GCCXML_GNUC_PATCHLEVEL__=p
         Defined to internal GCC parser patchlevel.

 From boost's point of view gccxml is another compiler identified by the 
above macros.  I know Boost.Config has some support for gccxml.  The 
header in question needs to be updated to not use the builtin when the 
compiler is identified as gccxml.  This is not the first time:

   https://svn.boost.org/trac/boost/ticket/907

For an immediate work-around you can install gcc 4.2 on your system and 
tell gccxml to simulate it with the option "--gccxml-compiler g++4.2".

-Brad