in yaml, a ~ key should allow to assing a value to the parent key

[rmanibus]

In Yaml spec, if one property is the prefix of another, a value can be attributed to the parent one using ~ as a null key to represent any YAML property that is a prefix of another one.

The following test is failing:

    public void testTildeIsDeserializedAsNullKey() throws Exception
    {
        final String YAML =
                "quarkus:\n" +
                        "  log:\n" +
                        "    sentry:\n" +
                        "      ~: true\n" +
                        "      dsn: 'some string'";

        JsonNode node = MAPPER.readValue(YAML, JsonNode.class);
        assertTrue(node.get("quarkus").get("log").get("sentry").booleanValue());
    }

instead, the following statement is true:

assertTrue(node.get("quarkus").get("log").get("sentry").get("~").booleanValue())

quarkus.log.sentry."~" is true instead of quarkus.log.sentry

Relevant conversation:

https://quarkusio.zulipchat.com/#narrow/stream/187038-dev/topic/yaml.20property.20conflict

Relevant spec:

https://quarkus.io/guides/config-yaml#configuration-property-conflicts

https://yaml.org/spec/1.2.2/

[rmanibus]

To clarify, this is causing issues with the Spotless formatter, it is basically transforming any ~ key in the "~" string

[cowtowncoder]

Quick question: how would you represent such document without ~ marker? Wouldn't there be problem with dsn key conflicting -- that is, there being both:

• quarkus.log.sentry = true
• quarkus.log.sentry.dsn = "some string"

which is impossible structurally?

Put another way; how would equivalent, non-tilde-using document look like?

[rmanibus]

I think you cannot, that's the whole point of the ~ key, it allows you to assign a value to a key that also has children

[cowtowncoder]

So could you not access quarkus.log.sentry.dsn in such case? Or is that simply dropped in such a case?

If there is no equivalent document, I don't think Jackson data model can represent this.
And if not, this is something that cannot really be supported -- it might actually be best to just throw an exception if so.

But I guess I am also not clear on point of using such marker.
I think I am missing something obvious.

EDIT: note, too, that link was to YAML 1.2 spec: Jackson 2.x uses SnakeYAML which supports YAML 1.1 only (https://bitbucket.org/snakeyaml/snakeyaml).
I don't know if tilde handling is part of 1.1 already.

[cowtowncoder]

Ohhh. Maybe it's effectively "empty" key? So something like JSON would have:

{ "quarkus": {
      "log": {
         "sentry": {
            "": true,
            "dsn": "some string"
         }
      }
   }
}

... although that would not be hidden by Jackson either; would need to be access with empty String as key.

EDIT: close, it is actually null key (similar to how "~" as value is same as null).

This is not something Jackson can represent since its data model does require all JsonToken.FIELD_NAME tokens to have String value. We could conceivably map it to empty String, becoming property with "" key. Not sure that'd be any better than leaving ~ as-is.

[cowtowncoder]

Based on all of above, I am pretty sure we cannot, in general make this work:

assertTrue(node.get("quarkus").get("log").get("sentry").booleanValue());

since "sentry" must be an Object value (with 2 logical properties; one with String key, other with null). I guess I don't know how YAML libraries generally would expose it either.

So the question would be whether to map ~ key to something else; and if so, to what?

[rmanibus]

The point of using this marker is to allow the use of yaml in configuration systems that have not initially been thought of with yaml in mind

[cowtowncoder]

Yeah the problem is that it does really map to JsonNode model (nor can I see an easy way to model it). In your case, either "null" key would need to replace value of sentry (so "sentry.dsn" would be lost), or we'd need a surrogate for "null" key.
For latter, empty String seems close enough -- but I am not sure TBH whether it'd be any more convenient to access than "~" key.

Put another way: what is being specifically asked is not doable. But I am open to ideas of alternative improvements.