Fix nested list expansion in JSON-LD

[avillar]

Summary of changes

This PR fixes parsing of deeply nested arrays in JSON-LD:

• by default:
  • Before fix: [ [ [ 1, 2, 3] , [4, 5] ] ] --> ( "[1, 2, 3]", "[4, 5]" ) (list contents converted to string literals)
  • After fix: [ [ [ 1, 2, 3] , [4, 5] ] ] --> ( 1 2 3 4 5 ) (array is properly flattened)
• when @container is set to @list:
  • Before fix: [ [ [ 1, 2, 3] , [4, 5] ] ] --> ( "[1, 2, 3]", "[4, 5]" ) (list contents converted to string literals)
  • After fix: [ [ [ 1, 2, 3] , [4, 5] ] ] --> ( ( ( 1 2 3 ) ( 4 5 ) ) ) (array nesting preserved)

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Checked that all tests and type checking passes.
• If the change adds new features or changes the RDFLib public API:
  • Created an issue to discuss the change and get in-principle agreement.
  • Considered adding an example in ./examples.
• If the change has a potential impact on users of this project:
  • Added or updated tests that fail without the change.
  • Updated relevant documentation to avoid inaccuracies.
  • Considered adding additional documentation.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[aucampia]

pre-commit.ci autofix

[aucampia]

I'm not really that familiar with JSON-LD as I probably should be, as far as I understand the flattening is pursuant to JSON-LD 1.1: 9.14 Property Nesting

[avillar]

@aucampia, yes, RDFLib does first-level and second-level flattening correctly, but fails when arrays are nested more deeply. For this JSON-LD playground example, this is what RDFLib outputs (note the incorrect "[4]"):

@prefix ns1: <http://example.com/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

[] ns1:a 1,
        2,
        3,
        5,
        "[4]" .

And, if @container is set to @list, flattening should not be happening at all. Again, JSON-LD Playground vs RDFLib output:

@prefix ns1: <http://example.com/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

[] ns1:a ( "[1, 2, 3]" "[[4]]" 5 ) .

[aucampia]

@avillar thanks for fixing this, and apologies for only reviewing it now. There are some minor comments that I will address with some commits shortly, but the fix looks very good overall.

[aucampia]

I will merge this before 2023-08-14.

[avillar]

Thank you, and thanks for all the fixes!

[coveralls]

coverage: 90.934% (+0.002%) from 90.932% when pulling 3041924 on avillar:fix-nested-arrays into f45bd9b on RDFLib:main.