Excluding `null` to match `skip_serializing_if = "Option::is_none"`

[lgarron]

I have some code like this:

pub(crate) struct PostVersionInfo {
    // …
    #[serde(skip_serializing_if = "Option::is_none")]
    magnitude: Option<VersionBumpMagnitudeType>,
}

This outputs a schema containing:

{
    // …
    "magnitude": {
      "anyOf": [
        {
          "$ref": "#/$defs/VersionBumpMagnitudeType"
        },
        {
          "type": "null"
        }
      ]
    }
}

This is not valid, as null is specifically not a possibility (and validation should fail if null is specified as the value).

It seems there are a few related issues about this, but I can't quite figure out if this is supposed to be supported. It would be nice if this either:

• happened automatically when skip_serializing_if = "Option::is_none" is specified, or
• had a simple attribute to exclude null as a valid field value in the output JSON.

[michaeltlombardi]

This used to be possible in pre-v1 versions of schemars with the SchemaSettings struct, for example:

let generator = SchemaSettings::draft2020_12().with(|s| {
    // More properly, the data should not be included in the object, instead of allowing
    // or expecting null values
    s.option_add_null_type = false;
}).into_generator()

I haven't yet found the correct way to recover this functionality in the v1 and later releases.

[lgarron]

I haven't yet found the correct way to recover this functionality in the v1 and later releases.

Ah, alas. 😭

If it will take time to figure out a proper solution, I'd appreciate any sort of temporary solution, e.g. an immediately-deprecated attribute just for this.

[michaeltlombardi]

My current plan is to write a transformer to handle it until there's a built-in way. Once I get that working I can share my implementation as a workaround.