Saxon

We're trying to evaluate a variable $v1 that has visibility="abstract" which of course is not possible.

It's easy enough to eliminate abstract variables from the pre-evaluation logic in Controller.preEvaluateGlobals(). The problem is that the variable is being evaluated by virtue of a reference from another global variable ($v1-proxy). This should be evaluating the overriding variable, but the logic to achieve this in the pre-evaluation pass seems to be absent.

The only solution I've been able to find for this is to abandon the attempt to pre-evaluate global variables when tracing.

It was always a bit questionable anyway - there's an argument that tracing should change the execution plan as little as possible.

The reason it's tricky is that the bindings from a global variable to other components depend on where it was called from. In the language of the spec, a global variable V in a used package results in a corresponding global variable V' in the using package, and their values may be different if V references components that are overridden in the using package. In terms of the implementation, a global variable can only really be evaluated in the context of a global variable reference, which provides the "current component" in the context. We're doing this pre-evaluation without setting a current component, and that's essentially why it crashes.

Removing the pre-evaluation reduces the number of test failures when running the test suite with -T to 55 (many of them in test set on-empty).