Saxon

Using Saxon-HE 9.9.1.5J, I have run into a problem when I try to use use current-merge-group() inside of xsl:merge-action but in an XPath expression that uses the simple map operator !; Saxon the refuses to run the code claiming there is no current merge group: "XTDE3480: There is no current merge group".

A much reduced and not very meaningful test case that demonstrates the problem is:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="3.0"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:mf="http://example.com/mf"
    expand-text="yes"
    exclude-result-prefixes="#all">
    
    <xsl:output indent="yes"/>
    
    <xsl:function name="mf:test" as="item()*">
        <xsl:param name="i1" as="xs:integer*"/>
        <result>{sum($i1)}</result>
    </xsl:function>
    
    <xsl:template match="/" name="xsl:initial-template">
        <root>
            <xsl:merge>
                <xsl:merge-source select="1 to 10">
                    <xsl:merge-key select=". idiv 5"></xsl:merge-key>
                </xsl:merge-source>
                <xsl:merge-action>
                    <xsl:message select="position(), ': ', current-merge-group()"/>
                    <xsl:sequence select="(1 to 3) ! mf:test(current-merge-group())"/>
                </xsl:merge-action>
            </xsl:merge>
        </root>
    </xsl:template>
    
</xsl:stylesheet>

Output when run from the command line with -it -xsl:map-expression-problem1.xsl:

Processing  (no source document) initial template = xsl:initial-template
1 :  1 2 3 4
Error evaluating (fn:sum(...)) in xsl:sequence/@select on line 23 column 87 of map-expression-problem1.xsl:
  XTDE3480: There is no current merge group. Found while atomizing the first argument of mf:test()
at template xsl:initial-template on line 15 of map-expression-problem1.xsl:
     invoked by unknown caller (null)
at template xsl:initial-template on line 15 of map-expression-problem1.xsl:
     invoked by unknown caller (null)
at template xsl:initial-template on line 15 of map-expression-problem1.xsl:
     invoked by unknown caller (null)
There is no current merge group. Found while atomizing the first argument of mf:test()

As the call to the mf:test is inside of an xsl:merge-action I think the current-merge-group() should be present. Somehow the use of the map operator ! seems to trigger this so I suppose that Saxon rewrites the code and doing it in a way that makes it claim that the merge group is absent.