Saxon

Thanks for reporting it. I have reproduced the problem, and have confirmed that it goes away if bytecode generation is disabled (which provides a workaround).

The problem has been fixed by a simple patch to ForEachGroupCompiler. It is another instance of a common bug that arose after we refactored Expression to no longer implement Location, but instead to have a getLocation method: in some cases IntelliJ's automatic refactoring added a getLocation() call inappropriately. In most cases Java's static typing detected this, but when it happened in bytecode generation the error is generally at execution time.

What's interesting now is the fact that this went undetected. A supplementary answer on the original StackOverflow report shows that the problem goes away if a call to current-grouping-key() is added to the stylesheet. It turns out that the expression implementing current-grouping-key() is not capable of generating bytecode, and the same is true for current-group(), which means that in nearly all cases the attempt to generate bytecode for an xsl:for-each-group instruction fails. The failure is silent and results in fallback to interpreted execution, which is why none of our tests picked up this issue.

I'm going to mark this issue as solved, and raise a new issue on the fact that bytecode isn't being generated for these function calls.

Bug fix applied in the Saxon 9.7.0.2 maintenance release