Better rendering for HashMaps w/ OpenAPI

[disconsented]

Is your feature request related to a problem? Please describe.
I've been trying to understand why the ToSchema doesn't render as expected, I've worked out that this is due to structs with HashMap<String, T> being expanded into a generic object type like below.

{
  "openapi": "3.1.0",
  "info": {
    "title": "inkwell api",
    "version": "0.0.1"
  },
  "paths": {},
  "components": {
    "schemas": {
      "document.Document": {
        "type": "object",
        "required": [
          "id",
          "order",
          "colour",
          "title",
          "category",
          "tags",
          "template",
          "fields"
        ],
        "properties": {
          "category": {
            "type": "string"
          },
          "colour": {
            "$ref": "#/components/schemas/block.Colour"
          },
          "fields": {
            "type": "object",
            "additionalProperties": true
          },
          "id": {
            "type": "string"
          },
          "order": {
            "$ref": "#/components/schemas/block.Numerical"
          },
          "tags": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/block.Phrase"
            }
          },
          "template": {
            "type": "string"
          },
          "title": {
            "type": "string"
          }
        }
      }
    }
  }
}

For anyone else who stumbles across the issue before it's resolved, I've worked around it by manually inserting the reference:

    if let RefOr::Type(Schema::Object(schema)) = doc
        .components
        .schemas
        .0
        .get_mut("document.Document")
        .expect("missing Document, has the schema changed?")
    {
        if let RefOr::Type(Schema::Object(fields)) = schema.properties.get_mut("fields").unwrap(){
            fields.additional_properties = Some(Box::new(AdditionalProperties::RefOr(RefOr::Ref(
                schema::Ref::new("#/components/schemas/block.BlockData"),
            ))));
        }
    }

Describe the solution you'd like
OpenAPI does support this kind of type (https://swagger.io/docs/specification/v3_0/data-models/dictionaries/), so it'd be good if we can reference other types here.

Going from:

Object {
    schema_type: Basic(
        Object,
    ),
    name: None,
    format: None,
    description: None,
    default_value: None,
    enum_values: [],
    required: {},
    properties: {},
    additional_properties: Some(
        FreeForm(
            true,
        ),
    ),
    deprecated: None,
    examples: [],
    write_only: None,
    read_only: None,
    xml: None,
    multiple_of: None,
    maximum: None,
    minimum: None,
    exclusive_maximum: None,
    exclusive_minimum: None,
    max_length: None,
    min_length: None,
    pattern: None,
    max_properties: None,
    min_properties: None,
    extensions: {},
    content_encoding: "",
    content_media_type: "",
}

To:

 Object {
    schema_type: Basic(
        Object,
    ),
    name: None,
    format: None,
    description: None,
    default_value: None,
    enum_values: [],
    required: {},
    properties: {},
    additional_properties: Some(
        RefOr(
            Ref(
                Ref {
                    ref_location: "#/components/schemas/SomethingElse",
                    description: "",
                    summary: "",
                },
            ),
        ),
    ),
    deprecated: None,
    examples: [],
    write_only: None,
    read_only: None,
    xml: None,
    multiple_of: None,
    maximum: None,
    minimum: None,
    exclusive_maximum: None,
    exclusive_minimum: None,
    max_length: None,
    min_length: None,
    pattern: None,
    max_properties: None,
    min_properties: None,
    extensions: {},
    content_encoding: "",
    content_media_type: "",
}

[chmln]

Yeah it looks like the ToSchema of the Value type is not used in the construction at all.

I was also able to work around it by creating a newtype around HashMap, but this should not be hard to fix for all hashmaps:

#[repr(transparent)]
pub struct MyMap<K: Hash + PartialEq + Eq, V>(pub HashMap<K, V>);

impl<K: Hash + PartialEq + Eq, V: ToSchema> ToSchema for MyMap<K, V> {
    fn to_schema(
        components: &mut salvo::oapi::Components,
    ) -> salvo::oapi::RefOr<salvo::oapi::schema::Schema> {
        let val = V::to_schema(components);
        salvo::oapi::schema::Schema::object(Object::new().additional_properties(val)).into()
    }
}