Add support for booleans and floats in OpenAPI Schema const

[flxdot]

We encountered the problem that the Pydantic Schemas for the OpenAPI spec, do not support the const keyword if it is of type boolean.

Why do I think it should be supported?

The OpenAPI Specification explicitly marks the const keyword as unsupported. Nevertheless it should not result in exceptions if the keyword is present.

I furthermore did not find any evidence in JSON Schema that would limit the types valid for the const keyword to be string or integer only.

Thus I suggest allowing boolean as well as floats as constant values.

Example

The following is minimal example in FastAPI that would produce such a schema:

from typing import Literal

import uvicorn
from fastapi import FastAPI
from pydantic import BaseModel, Field


class ResponseWithConstantBool(BaseModel):

    message: str = Field(...)
    is_welcome: Literal[True] = Field(True)


app = FastAPI()


@app.get("/", response_model=ResponseWithConstantBool)
async def root():
    return {"message": "Hello World"}


if __name__ == "__main__":
    uvicorn.run(app)

Generated OpenAPI Specification

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/": {
      "get": {
        "summary": "Root",
        "operationId": "root__get",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/ResponseWithConstantBool"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "ResponseWithConstantBool": {
        "properties": {
          "message": {
            "type": "string",
            "title": "Message"
          },
          "is_welcome": {
            "type": "boolean",
            "enum": [true],
            "const": true,
            "title": "Is Welcome",
            "default": true
          }
        },
        "type": "object",
        "required": [
          "message"
        ],
        "title": "ResponseWithConstantBool"
      }
    }
  }
}

[dbanty]

I believe OpenAPI 3.1 is what added support for const, but you're right, there's no reason it shouldn't support all the primitives. Thanks for the PR!