Re: [xsl] Use of XSLT 3 current-merge-group() as argument to user-defined function

["Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

This looks like a bug. It shouldn't be possible to call current-merge-group()
within the called function, but it should be possible to call it while
evaluating an argument of the function call.

The reason for the restriction is to reduce the amount of context that has to
be passed to functions/templates just in case it is needed, and to increase
the potential for static analysis. This is of course particularly important
for streaming, but it's useful elsewhere as well. And there was a desire to
have no needless differences between the streaming and non-streaming cases.

Michael Kay
Saxonica

> On 23 Aug 2018, at 19:21, Martin Honnen martin.honnen@xxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>
> I am trying to use the function current-merge-group inside of an
xsl:merge-action in a call to a user-defined function
>
>  <xsl:merge-action>
>     <xsl:sequence select="mf:my-fun(current-merge-group(),
$levels-to-reconstruct - 1)"/>
>  </xsl:merge-action>
>
> While that works fine with Altova I don't get it to work with Saxon 9.8,
even with HE or with a stylesheet not using streamable merge sources, Saxon
indicates "XTDE3480: There is no current merge group".
>
> Looking at the spec https://www.w3.org/TR/xslt-30/#dt-current-merge-group it
says "The current merge group and current merge key are available within the
sequence constructor contained by an xsl:merge-action element." and "All
invocation constructs set the current merge group and current merge key to
absent" where the section
https://www.w3.org/TR/xslt-30/#dt-invocation-construct then details "XPath
function calls that bind to stylesheet functions" as one of the invocation
constructs so Saxon seems to be following the spec to reject the use of
current-merge-group() as the argument to my function.
>
> I wonder why there is that restriction, at least when no streaming is used I
can't directly see a reason why a merge group can't be passed on to a
function.
>
> I can rewrite the code to
>
>  <xsl:merge-action>
>    <xsl:sequence select="let $group := current-merge-group() return
mf:my-fun($group, $levels-to-reconstruct - 1)"/>
>  </xsl:merge-action>
>
> to have it executed in Saxon as well.
>
> Why does the spec not allow passing current-merge-group() directly to a user
defined function?