Unused default functions may be generated

[ahl]

Consider this schema:

{
  "$defs": {
    "MaxPathConfig": {
      "type": "integer",
      "minimum": 1
    },
    "Thing": {
      "type": "object",
      "properties": {
        "max_path": {
          "default": 1,
          "allOf": [
            {
              "$ref": "#/$defs/MaxPathConfig"
            }
          ]
        }
      }
    }
  }
}

This generates this code for Thing:

#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug)]
pub struct Thing {
    #[serde(default = "defaults::thing_max_path")]
    pub max_path: MaxPathConfig,
}

Looks good! However, here's the default mod:

#[doc = r" Generation of default values for serde."]
pub mod defaults {
    pub(super) fn default_nzu64<T, const V: u64>() -> T
    where
        T: ::std::convert::TryFrom<::std::num::NonZeroU64>,
        <T as ::std::convert::TryFrom<::std::num::NonZeroU64>>::Error: ::std::fmt::Debug,
    {
        T::try_from(::std::num::NonZeroU64::try_from(V).unwrap()).unwrap()
    }
    pub(super) fn thing_max_path() -> super::MaxPathConfig {
        super::MaxPathConfig(::std::num::NonZeroU64::new(1).unwrap())
    }
}

Note that while thing_max_path is used, default_nzu64 is not and results in an unused code lint in generated code.