[Xapian-devel] Error handling in the bindings

[Richard Boulton]

Coming back to this topic - as you may have seen, I've committed to 
xapian-bindings some changes which reorganise the SWIG source files so 
that we can add language specific exception handling just by adding an 
"except.i" file to the source directory for the language in question - a 
default except.i file is used if this isn't present.  I've split the TCL 
exception handling and PHP exception handling into except.i files, 
because they were already significantly customised (with #ifdefs, and 
similar), but haven't yet committed anything which changes behaviour (as 
far as I can tell).

I've now got an uncommitted except.i file for Python which causes it to 
throw Xapian errors instead of the limited SWIG errors.  This seems to 
work fine, but I haven't yet made it use the full Xapian exception 
hierarchy (I've just wrapped Xapian::Error and a couple of the 
subclasses for test purposes).  So - the hard work is done.

I've just been looking at how to use generate-exceptions.in to generate 
the exception hierarchy for use by SWIG.  Sadly, my Perl is a bit rusty, 
so I quickly converted it to Python, and split the definitions of the 
exception heirarchy into a separate file.  This leaves me with two 
files, "generate-exceptions.in" which generates xapian/include/error.h 
and xapian/include/errordispatch.h, and "exception_data.py" which just 
initialises a load of python variables to represent the error hierarchy. 
  The point of this is that I can then write a separate 
generate-binding-exceptions.in in the xapian-bindings module which 
generates the exception hierarchy stuff for the bindings which need it, 
and this script can include the same "exception_data.py" file to get the 
definition of the hierarchy.

I have several questions:

1. Is it okay to require Python for maintainer mode builds of Xapian-core?

2. Is it okay to replace the Perl generate-exceptions.in with my Python one?

3. How best should I include exception_data.py from the xapian-bindings 
module.  My current thinking is to assume that the sources are laid out 
as assumed by bootstrap.sh if a maintainer mode build is in progress, 
and to look for exception_data.py in "$srcdir/../xapian-core/", but I'd 
like a better plan.  Perhaps I could add exception_data.py to the list 
of installed files (going in $prefix/share/xapian/ perhaps), and add an 
option to xapian-config.py which reported the directory it was installed in.

Once we've got such exception handling for Python sorted, it hopefully 
won't be too hard to implement it for PHP5, Ruby and CSharp - but I 
haven't looked at those at all yet.

-- 
Richard