Saxon

The options streamingFallback and jit are basically incompatible. If we use JIT compilation then we might not discover that a template rule is non-streamable until we're half way through processing the source document, and at this point we have streamable nodes (we haven't built a tree) so it's too late to switch to non-streaming. I think the simplest way to tackle this is that if streamingFallback has been requested, we ignore the request (and fail anyway) if a non-streamable template is found during JIT processing.

In the case of xsl:source-document we need to change the strategy. Currently this compiles into different code depending on the value of the streamable attribute. If fallback to non-streaming is necessitated because some template rule is non-streamable, it may be too late to recompile the xsl;source-document instruction. It therefore needs to be able to make a run-time switch into non-streamed execution - which is probably a good thing anyway, because it means we can give better diagnostics.

The changes here are starting to become sufficiently extensive that I think patching 9.8 to make this work is probably not a good idea. Instead I propose to fix the bug by dropping the feature (streaming fallback) on the 9.8 branch, and implementing it afresh on the development branch.