Turtle serializer mis‑normalizes xsd:boolean literal "true" as "false"

[alelom]

When using rdflib.js to create xsd:boolean literals and serialise them to Turtle, boolean literals with lexical form "true" are incorrectly serialised as "false". This appears to be a bug in the boolean normalisation logic used by the Turtle serializer.

According to the XSD and RDF specs for xsd:boolean, the lexical space is:

"true" → value true

"false" → value false

"1" → value true

"0" → value false

In the current rdflib.js behaviour, "true" is being normalised to the lexical form "false" on serialisation, which is not spec‑compliant.

Reproducible example

const $rdf = require('rdflib')

const XSD = $rdf.Namespace('http://www.w3.org/2001/XMLSchema#')

const store = $rdf.graph()
const subject = $rdf.sym('http://example.org/s')
const predicate = $rdf.sym('http://example.org/p')

// Four literals with xsd:boolean datatype and different lexical forms
const litTrue  = $rdf.literal('true',  null, XSD('boolean'))
const litFalse = $rdf.literal('false', null, XSD('boolean'))
const litOne   = $rdf.literal('1',     null, XSD('boolean'))
const litZero  = $rdf.literal('0',     null, XSD('boolean'))

store.add(subject, predicate, litTrue)
store.add(subject, predicate, litFalse)
store.add(subject, predicate, litOne)
store.add(subject, predicate, litZero)

$rdf.serialize(
  undefined,           // base
  store,
  'http://example.org/',
  'text/turtle',
  (err, ttl) => {
    if (err) {
      console.error(err)
      return
    }
    console.log(ttl)
  }
)

On my system, the relevant part of the Turtle output looks like:

<http://example.org/s> <http://example.org/p> false, false, true, false .

[melvincarvalho]

Hey @alelom, thanks for reporting this.

Looks like the issue is in src/serializer.js the boolean check only matches '1' but not 'true':

return expr.value === '1' ? 'true' : 'false'

I think adding || expr.value === 'true' to that condition should fix it.

[bourgeoa]

#147