Specifying default value for an object should use object's existing default field values

[jamesthurley]

Let's say I have the following object definition in my schema:

"SeparatorConfig": {
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "lineThickness": {
      "type": "integer",
      "default": 1
    },
    "lineColor": {
      "type": [
        "string",
        "null"
      ],
      "default": "#B2000000"
    }
  }
},

So SeparatorConfig has two properties, both of which have default values.

Elsewhere in another object I have a field of type SeparatorConfig, and I'd like to make the entire field optional such that it defaults to an object with the correct default field values as defined above.

I could in theory do the following:

"separator": {
  "$ref": "#/definitions/SeparatorConfig",
  "default": {}
},

However the resulting generated code which produces this default value is:

super::SeparatorConfig {
  line_color: Default::default(),
  line_thickness: Default::default(),
}

Which produces:

{
  "line_color": null,
  "line_thickness": 0
}

Rather than the desired default:

{
  "line_color": "#B2000000",
  "line_thickness": 1
}

A better implementation for creating the default SeparatorConfig struct would be to use the existing builders you already generate:

builder::SeparatorConfig::default().try_into().expect("default should be valid")

We would also have to use the builder functions for defaults which specify only some properties:

"separator": {
  "$ref": "#/definitions/SeparatorConfig",
  "default": { "lineThickness": 5 }
},

Could produce:

builder::SeparatorConfig::default()
  .line_thickness(5_i64)
  .try_into()
  .expect("default should be valid")

rather than the current:

super::SeparatorConfig {
  line_color: Default::default(),
  line_thickness: 5_i64,
}

Overall this would make specifying default values for objects throughout a schema significantly easier.

The current alternatives are to either specify all the default field values at every level, duplicating a lot of default values (error prone), or not specifying defaults in the schema and manually constructing default structs in code when properties are None (cumbersome).

[ahl]

Great issue; agreed on points you're making.