true() in XPath predicates

[timathom]

I am able to use the true() function in MIP XPath expressions, but it doesn't seem to work in control @ref predicates.

The example below throws an error when I try to use true() in a predicate (log output).

fontoxpath.esm.js:278 Uncaught (in promise) Error: XPST0017: Function Q{http://www.w3.org/2002/xforms}true with arity of 0 not registered. Did you mean "Q{http://www.w3.org/2005/xpath-functions}true ()"?

<fx-fore>
  <fx-model>
    <!-- Instance data -->
    <fx-instance>
      <data>
        <response>
          <one yes="true">This is true.</one>
          <two yes="false">This is false.</two>
        </response>
      </data>
    </fx-instance>
    <!-- /Instance data -->
  </fx-model>
  
  <!-- This works. -->
  <fx-output ref="response/*[@yes = 'true']"></fx-output>
  
  <!-- This doesn't. -->
  <fx-output ref="response/*[@yes = true()]"></fx-output>
  <fx-inspector open="true"></fx-inspector>
</fx-fore>

[timathom]

I seem to be getting the same error with not(), which is more problematic:

Uncaught (in promise) Error: XPST0017: Function Q{http://www.w3.org/2002/xforms}not with arity of 1 not registered. Did you mean "Q{http://www.w3.org/2005/xpath-functions}not (item()*)"?

[JoernT]

well - response/*[@yes = true()] is not true as it compares a boolean to a string - so that's correct.

There's a boolean-from-string function for such cases that is adopted from XForms.

However of course it shoudn't throw an error.

[timathom]

In BaseX,

let $test := <response yes="true"/>
return $test/@yes = true()

returns true.

Same result in Fonto.

[JoernT]

hm, okay - that's evidence ;) Needs more investigation.

[DrRataplan]

Hm, this might be because the namespace overriding is not kicking in. In xpath-evaluation.js, there's this part: https://github.com/Jinntec/Fore/blob/dev/src/xpath-evaluation.js#L274 which tries to align the different prefixes. It tries to make xforms and fn fucntions available w/o a prefix. This must be going wrong here...

[JoernT]

just found in my use case that using 'fn:' prefix did the trick for me.

The globallyDeclaredFunctionLocalNames array is empty for some reason.

So this part is failing:

            if (prefix === '' && globallyDeclaredFunctionLocalNames.includes(localName)) {
                // The function has been declared without a prefix and is called here without a prefix.
                // Just make this work. It is the developer-friendly way
                return {namespaceURI: 'http://www.w3.org/2005/xquery-local-functions', localName};
            }

[JoernT]

I'll convert this discussion to an issue.

[JoernT]

workaround

Use 'fn:' prefix for core XPath functions

[DrRataplan]

I think I found it: for these functions, the correct functionNameResolver wasn't passed. See #155 for the fix!

[JoernT]

so its fixed and i mark this as answered