Saxon

SaxonCS 11.4 also gives an exception:

Analyzing query from .\fail.xqy
Analysis time: 500,7252 milliseconds
<?xml version="1.0" encoding="UTF-8"?>Saxon.Hej.trans.UncheckedXPathException
 ---> Saxon.Hej.trans.XPathException: Cannot add a map to an XDM node tree
   at Saxon.Hej.expr.Expression.process(Outputter output, XPathContext context)
   at Saxon.Hej.expr.SystemFunctionCall.process(Outputter output, XPathContext context)
   at Saxon.Hej.expr.instruct.ElementCreator.processLeavingTail(Outputter out, XPathContext context, NodeInfo copiedNode)
   at Saxon.Hej.expr.instruct.ElementCreator.processLeavingTail(Outputter output, XPathContext context)
   at Saxon.Hej.expr.instruct.Instruction.process(Outputter output, XPathContext context)
   at Saxon.Hej.expr.parser.Evaluator.Process.evaluate(Expression expr, XPathContext context)
   at Saxon.Hej.expr.TailCallLoop.tailCallDifferentFunction(UserFunction userFunction, XPathContextMajor cm)
   at Saxon.Hej.expr.TailCallLoop.iterate(XPathContext context)
   at Saxon.Hej.value.MemoClosure.makeSequence()
   at Saxon.Hej.value.MemoClosure.iterate()
   --- End of inner exception stack trace ---
   at Saxon.Hej.value.MemoClosure.iterate()
   at Saxon.Hej.om.SequenceTool.process(Sequence value, Outputter output, Location locationId)
   at Saxon.Hej.expr.instruct.UserFunction.process(XPathContextMajor context, Sequence[] actualArgs, Outputter output)
   at Saxon.Hej.expr.UserFunctionCall.process(Outputter output, XPathContext context)
   at Saxon.Hej.query.XQueryExpression.run(DynamicQueryContext env, Result result, Properties outputProperties)
   at Saxon.Hej.s9api.XQueryEvaluator.run(Destination destination)
   at Saxon.Hej.Query.runQuery(XQueryExecutable exp, XQueryEvaluator evaluator, Source input, Destination destination)
   at Saxon.Hej.Query.doQuery(String[] args, String command)
Fatal error during query: UncheckedXPathException:

I've added code to SequenceTool.process() that converts the unchecked exception to a (checked) XPathException, and this improves the diagnostics:

Error on line 45 column 11 of badframework.xqy:
  XQTY0105  Cannot add a map to an XDM node tree
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by function call at file:/Users/mike/bugs/2022/5641-Holstege/badframework.xqy#53
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by unknown caller (class net.sf.saxon.value.MemoClosure)
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by function call at file:/Users/mike/bugs/2022/5641-Holstege/fail.xqy#21
Query failed with dynamic error: Cannot add a map to an XDM node tree

I think we could do better than this by including the result of Err.depict(map) in the error message; in this example this would show the offending map as map{"resolution":"medium"}. We also know that the element we are writing is called art:canvas, and I think we could work that in too.

With this change we get the diagnostics

Error on line 45 column 11 of badframework.xqy:
  XQTY0105  Cannot add a map (map{"resolution":"medium"}) to an XDM node tree (currently
  writing element art:canvas)
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by function call at file:/Users/mike/bugs/2022/5641-Holstege/badframework.xqy#53
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by unknown caller (class net.sf.saxon.value.MemoClosure)
     Focus: absent
     Local variables
        $externals = map{"ALGORITHM-PARAMETERS":map{},"CONTENT-FUNCTION":this:content}
     invoked by function call at file:/Users/mike/bugs/2022/5641-Holstege/fail.xqy#21
Query failed with dynamic error: Cannot add a map(map{"resolution":"medium"}) to an XDM node tree (currently writing element art:canvas)

Hopefully this resolves the issue.