Using riot with `N-Quads` input with named graphs and `N-Triples`/`Turtle` output silently drops part of the input

[aucampia]

Version

4.8.0

What happened?

Given this N-Quads input (saved as test/data/variants/diverse_quads.nq) that contains triples with graphs labels [ref] (i.e. contains named graphs[ref]):

<http://example.com/subject> <http://example.com/predicate> "日本語の表記体系"@jpx <example:graph> .
<urn:example:subject> <example:predicate> <example:subject> <example:graph> .
<example:subject> <example:predicate> <example:object> <example:graph> .
<example:subject> <example:predicate> "12"^^<http://www.w3.org/2001/XMLSchema#integer> <example:graph> .
<example:subject> <example:predicate> <example:object> <urn:example:graph> .
<example:subject> <http://example.com/predicate> <http://example.com/object> <urn:example:graph> .
<example:subject> <http://example.com/predicate> "XSD string" <urn:example:graph> .
<example:subject> <example:predicate> <example:object> .
<http://example.com/subject> <http://example.com/predicate> "typeless" .
<urn:example:subject> <urn:example:predicate> <urn:example:object> .

When processing it with riot --syntax=nquads --formatted=ntriples, riot generates output and no error, but the output only contains the triples from the default graph.

$ jbang run --main riotcmd.riot --deps='org.slf4j:slf4j-simple:1.7+' 'org.apache.jena:jena-cmds:4.8.0' --syntax=nquads --formatted=ntriples test/data/variants/diverse_quads.nq; echo status=$?
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
<http://example.com/subject> <http://example.com/predicate> "typeless" .
<example:subject> <example:predicate> <example:object> .
<urn:example:subject> <urn:example:predicate> <urn:example:object> .
status=0

I would expect it to at least exit with an error status code, and also preferably print an error message.

Relevant output and stacktrace

No response

Are you interested in making a pull request?

Maybe

[afs]

This can be changed as a feature request. To preserve streaming, it would be a once per run log message.

Jena treats quads in a triples context as triples from the default graph.

Some people expect the union-merge but named graphs might be being used for intentional separation.
The application has to indicates that the named graphs can be considered part of a union-all graph.
An option to riot to do the quads to triples conversion, controlled by a new argument, is possible.

[afs]

Please review #1876

[afs]

Also - added --merge

This is all about the command line tool and how it configures the operations.