Bug 11815 – XPathEvaluator behavior does not match Firefox - substring() and empty element

• Component: XML
• Status: RESOLVED FIXED

[Jesse Costello-Good]

The following test cases do not behave the same in Safari as in Firefox.

[Jesse Costello-Good]

// #1:
// An empty node value causes the substring() function to return true when it should return false.

var strXML = '<data><record id="-a-"></record><record id="a-a">-hi-</record></data>';
var doc = (new DOMParser()).parseFromString(strXML, "text/xml");
var xpe = new XPathEvaluator();
var objResult = xpe.evaluate("//record[substring(.,1,1)='-']", doc, null, 0, null);
var itm = null;
var objNodes = [];
while (itm = objResult.iterateNext()) objNodes.push(itm);

assertEquals(1, objNodes.length); // Safari yields 2

[Jesse Costello-Good]

// #2
// function name() does not work with attribute nodes

var strXML = '<data><record id="-a-" a="v">???</record><record id="a-a">{abc}</record></data>';
var doc = (new DOMParser()).parseFromString(strXML, "text/xml");
var xpe = new XPathEvaluator();
var objResult = xpe.evaluate("//@*[name()='id']", doc, null, 0, null);
var itm = null;
var objNodes = [];
while (itm = objResult.iterateNext()) objNodes.push(itm);

assertEquals(2, objNodes.length); // Safari yields 0

[Jesse Costello-Good]

I split this out in to two different issues. #2 is moved to bug 12340.

[Alexey Proskuryakov]

This appears to be a general problem in our XPath code - all C++ string literals are treated as boolean values.

Easy to fix by adding another constructor to XPath::Value, but I cannot understand how this occurs; suspecting a gcc bug. Please tell me I'm wrong :-). Test case:

-----------------------
#include <stdio.h>

class String {
public:
  String(const char*) {}
};

class Value {
public:
  Value(bool) { printf("bool\n"); }
  Value(const String&) { printf("String\n"); }
};

int main()
{
  Value val("");
}
-----------------------

[David Kilzer (:ddkilzer)]

(In reply to comment #4)
> This appears to be a general problem in our XPath code - all C++ string
> literals are treated as boolean values.
> 
> Easy to fix by adding another constructor to XPath::Value, but I cannot
> understand how this occurs; suspecting a gcc bug. Please tell me I'm wrong :-).

I believe this Google Groups thread answers it:

http://groups.google.com/group/comp.lang.c++/browse_thread/thread/73ab483d2ef241c/487423eb73ee10d6%23487423eb73ee10d6

[Alexey Proskuryakov]

The replies in this thread point out that pointers can be converted to bool - but a string literal is not a pointer, it's "const char[n]" (with a deprecated conversion allowing it to be converted to char*).

OTOH, the two transformations needed to get from a string literal to a bool fall into different categories (lvalue transformation and conversion), and are thus allowed in a standard conversion sequence, see section 13.3.3.1 of the standard. Not that I can claim complete understanding now, but I'm convinced.

[Alexey Proskuryakov]

Created attachment 12721 [details]
proposed fix

[Darin Adler]

Comment on attachment 12721 [details]
proposed fix

r=me

[Alexey Proskuryakov]

Committed revision 19225.