XPath Generator hits the trunk

After eighteen months of “try, try again”, the first version of XPath Generator code has landed in Mozilla 1.9 “trunk” code. It is currently off by default.

I’m quite pleased with this. This is the first complete feature I’ve driven from initial API drafts to a final implementation in Mozilla CVS.

So how do you use it? First, you need a build with ac_add_options -enable-extensions=default,xpath-generator. Once you have it, your chrome code should be able to call:

var generator = new XPathGenerator();
generator.addNamespace("html", "http://www.w3.org/1999/xhtml"); // optional, but recommended
var xpath = generator.generateXPath(targetNode, contextNode);

nsIXPathGenerator details two currently supported flags for the generator’s searchFlags property

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. IGNORE_ID_TYPE_ATTRS means that the XPath should not stop when it finds an ancestor with an ID attribute. USE_DESCENDANT_AXIS produces a single-step (in the case of attributes, double-step) XPath beginning with descendant::.

XPath Generator objects also provide their own namespace resolvers, which as I note above can take new namespace declarations via the generator’s addNamespace() method.

Sadly, this implementation excludes support for attributes in the XPath (foo[bar=”baz”]); based on review feedback it didn’t seem necessary for the initial implementation.

So why is this feature off by default? It’s new. Aside from myself, I don’t know anyone actively using my XPath Generator right now. Because it’s so new and untried, we (myself and the reviewers) decided we should not expose the generator to web pages just yet. For that reason, we left it off by default as well. Finally, because it wasn’t on by default, it didn’t land for the 1.9a7 milestone.

If you are a developer and you see yourself needing or wanting XPath Generator, you have two options. (1) Start playing with it now, and see what improvements you’d suggest (patches welcome). Your experiences with XPath Generator – including actually using it – will carry weight in any attempt to get it approved for Firefox 3. (Popular opinion & votes will not.)

(2) Package XPath Generator as an extension and submit it to AMO, and include it with your own extension as a multi-item package. If you’re going to do the latter, please contact me and let me know. Ideally, it would be submitted only once.

Either way, I really would like to find out how useful you find XPath Generator in your own work.

In the meantime, I need to work on making it and other extensions available to all Gecko-based apps

Oh, by the way, there’s also a new do_parse_document() function available for XPCShell tests. If you have a particularly slow Mochikit test that doesn’t need a window, you might want to rewrite your test to work using this new function. (Come to think of it, there could be a significant speed-up in total test execution, if we converted many tests and if text/html for DOMParser landed.)

(Now why do my most significant events take place on weekends…)