I am running Lua with a C++ library via swig. When a swig runtime error occurs I would like to know the line which caused the problem. The error message I receive does not have this information.
How can I find which line in the Lua code triggered the error?
For example suppose I have a swig function "swigstringcount" and it takes a string:
local n=4
local m=swigstringcount(n)
print (m,n)
This (obviously wrong) code produces an error on line two. Currently all I get is
error:SWIG_RuntimeError: swigstringcount requires a string
I want it to tell me that line 2 produced the error, like standard Lua error messages.
Based on this method for getting debug info from the Lua C API I've put together a (slightly messy) example of how you can integrate that into a SWIG interface:
%module test
%{
#undef SWIG_fail_arg
#define SWIG_fail_arg(func_name,argnum,type) \
{lua_Debug ar;\
lua_getstack(L, 1, &ar);\
lua_getinfo(L, "nSl", &ar);\
lua_pushfstring(L,"Error (%s:%d) in %s (arg %d), expected '%s' got '%s'",\
ar.source,ar.currentline,func_name,argnum,type,SWIG_Lua_typename(L,argnum));\
goto fail;}
%}
%include <std_string.i>
%inline %{
void func(const std::string& str) {}
%}
This basically replaces the default SWIG_fail_arg
macro with a modified one that gets and prints some debug info.
I tested it with the latest SWIG trunk (I think you might be using an older version since the text I see didn't quite match), but I was able to do:
Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio
> require('test')
> local n=4
> test.func(n)
Error (=stdin:1) in func (arg 1), expected 'std::string const &' got 'nil'
stack traceback:
[C]: in function 'func'
stdin:1: in main chunk
[C]: ?
I seem to have more debug info (i.e. a full stack trace) there already though.