Saxon

The fn:transform() code is not setting the global context item before invoking Controller.applyTemplates(). It should do so: simple bug, easy to fix.

This leaves the question, why does it work when tracing is not enabled?

Well, Controller.globalContextItem is being set to the initial source doc in Controller.transformDocument() at #2286. This seems incorrect. But how come it doesn't happen when tracing is enabled? Well, this is because, with tracing enabled, global variables are evaluated eagerly (so that the trace output is intelligible). In fact, they are initialized before Controller.transformDocument (incorrectly) sets the global context item.

The primary fix here is to ensure that fn:transform calls Controller.setGlobalContextItem() if the source-node option is present. This is straightforward (though it suggests the need for a couple of extra test cases).

The secondary problem, of preventing globalContextItem being set on the applyTemplates() path, is trickier, because the same code is used in a wide variety of situations and there is a serious risk of causing regression to other workloads. Nevertheless, it's clearly wrong, and it could cause worse problems than simply a failure to throw XPDY0002: it could cause the global context item to have the wrong value. So I shall try and correct this one too.

Fix committed:

1. fn:transform now correctly sets the global context item taking into account the two options source-node and global-context-item

2. Controller.transformDocument() no longer sets the global context item to the supplied source node; instead, callers of this function that require this behaviour do it themselves.

Bug fix applied in the Saxon 9.8.0.5 maintenance release.