Conditional attributes cause duplication of template code

[line-o]

Consider an element that needs to have an attribute set when a certain configuration value is set (non-empty).
So, attribute test should only be set if $config?test is anything else but the empty sequence.
Currently this is only possible way do express this is by writing

[% if (empty( $config?test )) %]
<my-element />
[% else %]
<my-element test="[[ $config?test ]]"/>
[% endif %]

When we now have two or more of those conditional attrbutes the element template has to be duplicated for each possible combination of those flags.
This is not feasible and error prone.

[DrRataplan]

I'd propose to change the code generation here, if an attribute expression resolves to the empty sequence, do not output the attribute. If it results in one or more items, output the attribute like we do now.

For the input:

<my-element test="[[ $config?test ]]"/>

Current output from jinks-templating:

<my-element test="{tmpl:valueOf($config?test)}"/>

Proposed out:

<my-element>
  {
    let $tmpl:r := tmpl:valueOf($config:test)
    return if (empty($tmpl:r)) then () else attribute test {$tmpl:r}
  }
</my-element>

This is breaking of course. In the old situation you could make attributes with empty values by returning empty sequences in the expression. In the new situation we would not output the attribute. This can be resolved of course on the input by writing something like <my-element test="string(config?test)"/>

[wolfgangmm]

I would instead propose a templating environment for attributes:

[% attribute attr %]...[% endattribute %]

Implementing this I was hitting some obstacles though, mainly because you need to be in the correct XQuery context.

[DrRataplan]

I think with that proposal the example @line-o gave would end up like this:

<my-element>
[% if (exists( $config?test )) %]
[% attribute test %]
[[ $config?test ]]
[% endif %]
[% endattribute %]
</my-element>

This feels quite verbose to be honest. And we'd like some convention (or enforced rule) to prevent something like this:

<my-element>
  <my-child>
  </my-child>
  [% attribute attr%]bla[% endattribute %]
</my-element>

Or more fun:

<my-element>
  [% for $x in 1 to 10 %]
  [% attribute attr%]bla[% endattribute %]
  [% endfor %]
</my-element>