Re: [xml] docs and dicts in xmlSetTreeDoc()

[Daniel Veillard <veillard redhat com>]

On Fri, May 02, 2008 at 06:06:41PM +0200, Stefan Behnel wrote:
> Hi,
> 
> I've just fixed a long-standing problem in lxml, now I'm wondering if it isn't
> actually a problem in libxml2. The function xmlSetTreeDoc() in tree.c is
> called to update the xmlDoc* pointers of each node in a subtree when it gets
> appended to a new parent in a different document. The question is: should this
> function also re-assign the "name" pointers of the nodes if both documents use
> a dict and the dictionary of the target document is different from the
> dictionary of the source tree?
> 
> The decision is easy to take (compare the dict pointers of both documents) and
> the code to re-assign the name is simple: call xmlDictLookup() and re-assign
> the name of the node to the result. In addition, a call to
> xmlDictOwns(old_dict, old_name) might be necessary to see if the old name must
> be freed.
> 
> Would this be considered worth changing? Or are there any reasons not to do
> this? There obviously is a performance impact, but I consider it the correct
> thing to do if both documents are meant to be independent afterwards.

  yes there is a performance impact for doing so. Still this may make sense,
though for applications which copy tree fragments around, it's best to use
the XML_PARSE_NODICT parsing option and limit the contextual dependancies
for nodes (limit, not remove, entities and namespace references come to mind).

Daniel

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