Saxon

What happens when a stylesheet is imported more than once is that we create two components with different import precedence but pointing to the same source code (specifically, StyleElement node in the stylesheet tree). When we compile components, we set a flag "compile action completed" which prevents a component being processed twice; but this flag is set in the StyleElement, not in the component, so the second component is not processed. But the two template components point to different NamedTemplate objects containing the compiled code, and so one of these NamedTemplate objects has a null body because the compilation wasn't carried out.

More precisely: there is one XSLTemplate object, but because there are two "declarations" (with the same source code but difference precedence) we call the index() method twice, and when we call the index() method, we create a new NamedTemplate object and update the value of XSLTemplate.compiledNamedTemplate to point to it. So we have created two NamedTemplate objects, and because of the (somewhat random) order of processing, the CallTemplate instruction points to the one that was abandoned and overwritten.

The index() method contains a chunk of commented-out code saying:

        // Following change was attempted to fix a problem with multiple includes, but
        // it caused other tests to crash e.g. apply-imports-001. MHK 2017-03-07

so it looks like we've been here before.