[webkit-dev] gdom_x_path_evaluator_create_ns_resolver [was: webkit #16401]

[Luke Kenneth Casson Leighton]

On 6/8/09, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> > Well I tried:
>  >
>  >
>  >     GdomXPathResult *res;
>  >     char* exp = "//html:select";
>  >     GdomDocument *doc = get_dom_document();
>  >     GdomNodeList *els = gdom_document_get_elements_by_tag_name(doc,
>  >  "body");
>  >     GdomNode *body = gdom_node_list_item(els, 0);
>  >     GdomXPathNSResolver *resolver =
>  >  gdom_document_create_ns_resolver(doc, body);
>  >
>  >
>  >     g_warning("init completed");
>  >
>  >     gdom_document_evaluate(doc, exp, GDOM_NODE(body), resolver, 0, res);
>  >
>  >  The warning is printed followed by a segfault.
>  >
>  >  gdb told me (relevant parts):
>  >
>  >  #0  0x00007fb6215ea058 in g_type_check_instance_cast () from
>  >  /usr/lib/libgobject-2.0.so.0
>  >  #1  0x00007fb623d21cb9 in WebKit::core () from
>  >  /usr/local/lib/libwebkit-1.0.so.2
>  >  #2  0x00007fb623cc55ab in gdom_document_evaluate () from
>  >  /usr/local/lib/libwebkit-1.0.so.2
>  >
>  >  It seems like an argument is broken.
>
>
>  hmm, i'm guessing it's the uninitialised last argument (from the
>  g_type_check_instance_cast) but it could equally, athough unlikely, be
>  the body arg.
>
>   you really need to recompile some of these object files with debug
>  info. try rm DerivedSources/gdom/*GdomDocument*.lo, do export CXX=gcc
>  -g -g, re-run configure etc.  that will get you _just_ debug info in
>  the gdom_document_* functions which will be enough for the purposes
>  here, without forcing you to recompile absolutely damn everything.
>
>   but yes - try NULL on that last argument (just a guess, here) err
>  nope, no can do, there - take a look at
>  DerivedSources/gdom/GdomDocument.cpp:
>
>
>  GdomXPathResult *
>  gdom_document_evaluate (GdomDocument *thiz, gchar * expression,
>  GdomNode * context_node, GdomXPathNSResolver * resolver, gushort type,
>  GdomXPathResult * in_result)
>
> {
>     ....
>     ....
>     WebCore::XPathResult * _g_in_result = WebKit::core(in_result);
>     g_return_val_if_fail (_g_in_result, 0);
>     ....
>  }
>
>  so - nope, in_result cannot be NULL, and you absolutely must _not_
>  pass in an uninitialised variable, either.
>
>  so - you're going to have to find a GdomXPathResult instance from somewhere.
>
>  keep looking around for documentation on this function, i'll do
>  likewise: if anyone has anything to contribute that can help leon out,
>  it would be appreciated.
>

from a random google search, leading to this:
http://www.faqts.com/knowledge_base/view.phtml/aid/34022

a code snippet is this:

// test with no prefix doesn't find nodes:
var xpathResult = xmlDocument.evaluate(
  "//element",
  xmlDocument,
  null,
  XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,
  null
);

showing that yes, it should be possible to pass in NULL as that last argument.

hmmm, ok, gimme 1 sec, i'll just update CodeGeneratorGObject.pm so it
can accept NULL arguments and pass them on...