#633 Saxon-SA incorrect filter optimization

Michael Kay

Saxon-SA may carry out an incorrect optimization of certain filtered path expressions. The expressions in question take the form


where it is known by static analysis that the context item will be a document node. In such cases Saxon attempts to treat the expression as /a/b/c[d=f], because this enables a rewrite to use a document-level index. However this rewrite is done incorrectly, with the likely consequence that no data will be selected.

Workaround: add a leading "/" to the path expression.

A patch is being placed in Subversion, it affects method isAbsolute in net.sf.saxon.expr.PathExpression. However, the patch will of course only be effective when the patched module is incorporated in a build of Saxon-SA. The effect of this patch is merely to remove the attempt at optimization; the source clearance will make the optimization work properly.


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