Set "default" on generated schemas

[GREsau]

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Is it possible to get it to output default values for the generated schema, as provide by Default/SmartDefault?

JSON Schema "default" keyword reference: https://json-schema.org/draft/2019-09/json-schema-validation.html#rfc.section.9.2

Example 1

#[derive(Debug, Default, Deserialize, Serialize, JsonSchema)]
#[serde(default)]
pub struct MyStruct {
    pub my_int: i32,
    pub my_bool: bool,
}

The generated schema for MyStruct should be:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "MyStruct",
  "type": "object",
  "properties": {
    "my_bool": {
      "type": "boolean",
      "default": false
    },
    "my_int": {
      "type": "integer",
      "format": "int32",
      "default": 0
    }
  }
}

Note that we set default on the properties, not on the top-level schema for MyStruct.

Example 2

It gets more complicated when we use #[serde(default)] on fields as well as the struct, e.g.

fn ten_and_true() -> MyStruct2 {
    MyStruct2 {
        my_int: 10,
        my_bool: true,
    }
}

fn six() -> i32 {
    6
}

#[derive(Default, Deserialize, Serialize, JsonSchema, Debug)]
#[serde(default = "ten_and_true")]
pub struct MyStruct2 {
    #[serde(default = "six")]
    pub my_int: i32,
    pub my_bool: bool,
}

The generated schema for MyStruct2 should be:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "MyStruct2",
  "type": "object",
  "properties": {
    "my_bool": {
      "type": "boolean",
      "default": true
    },
    "my_int": {
      "type": "integer",
      "format": "int32",
      "default": 6
    }
  }
}

Example 3

fn ten_and_true() -> MyStruct2 {
    MyStruct2 {
        my_int: 10,
        my_bool: true,
    }
}

fn six() -> i32 {
    6
}

#[derive(Default, Deserialize, Serialize, JsonSchema, Debug)]
#[serde(default)]
pub struct MyStruct {
    pub my_int: i32,
    pub my_bool: bool,
    pub my_struct2: MyStruct2,
}

#[derive(Default, Deserialize, Serialize, JsonSchema, Debug)]
#[serde(default = "ten_and_true")]
pub struct MyStruct2 {
    #[serde(default = "six")]
    pub my_int: i32,
    pub my_bool: bool,
}

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "MyStruct",
  "type": "object",
  "properties": {
    "my_bool": {
      "type": "boolean",
      "default": false
    },
    "my_int": {
      "type": "integer",
      "format": "int32",
      "default": 0
    },
    "my_struct2": {
      "allOf": [{"$ref": "#/definitions/MyStruct2"}],
      "default": {
        "my_bool": false,
        "my_int": 0
      }
    }
  },
  "definitions": {
    "MyStruct2": {
      "type": "object",
      "properties": {
        "my_bool": {
          "type": "boolean",
          "default": true
        },
        "my_int": {
          "type": "integer",
          "format": "int32",
          "default": 6
        }
      }
    }
  }
}

Note that the default for the my_struct2 property has different property defaults (false/0) than the defaults in the MyStruct2 definition (true/6). This is because:

• Deserializing {} to MyStruct results in MyStruct { my_int: 0, my_bool: false, my_struct2: MyStruct2 { my_int: 0, my_bool: false } }
• While deserializing {"my_struct2": {}} results in MyStruct { my_int: 0, my_bool: false, my_struct2: MyStruct2 { my_int: 6, my_bool: true } }

[GREsau]

Implemented in v0.6, now published to crates.io