Panic on empty discriminator mapping about json-typedef-codegen HOT 2 OPEN

Hi, thanks for taking the time to report this bug report!

This is indeed a bug. The schema you provided is in fact not a valid JSON Type Definition schema -- the schema at /properties/bar/mapping/foo is of the empty form, but mapping schemas must be of the properties form -- but jtd-codegen should be providing a clear error message to this effect, and certainly shouldn't be panicking.

A bit more details on what schemas can appear inside mappings is covered here: https://jsontypedef.com/docs/jtd-in-5-minutes/

You can only use properties / optionalProperties / additionalProperties in the schemas you put directly in mapping. You can’t use any other kind of schema, otherwise things would become ambiguous.

Admittedly, that language is a bit loose, and I understand how you would think that using no keywords at all would be kosher. The RFC is a bit more explicit: https://tools.ietf.org/html/rfc8927#section-2

   ; discriminator describes the "discriminator" schema form.
   ;
   ; There are additional constraints on this form that cannot be
   ; expressed in CDDL. Section 2.2.8 describes these additional
   ; constraints in detail.
   discriminator = (
     discriminator: tstr,
     ; Note well: this rule is defined in terms of the "properties"
     ; CDDL rule, not the "schema" CDDL rule.
     mapping: { * tstr => { properties } }
     shared,
   )

But again: jtd-codegen should not be leaving you out to dry like this.

In the immediate term, I suspect you'll have success if you alter your schema to be a valid JTD schema. For instance, just adding "properties": {} to foo would make your schema valid. This schema seems to work, at least for me:

{
    "properties": {
        "tag": {
            "enum": [
                "foo"
            ]
        },
        "bar": {
            "discriminator": "tag",
            "mapping": {
                "foo": {
                    "properties": {}
                }
            }
        }
    }
}

In the longer term, the jtd-codegen bug here is that the tool should validate a schema's correctness before attempting to generate code from it, and produce an error message rather than generate code (and ultimately crash).

from json-typedef-codegen.

Thank you for the prompt reply, and for taking the time to explain!

from json-typedef-codegen.