Incorrect sample URLs when no "server" is included in the OpenAPI spec

[jeroenheijmans]

My OpenAPI json spec generated by a .NET Core API, is presumably handled incorrectly by Redoc. My OpenAPI spec looks like this:

{
  "openapi": "3.0.1",
  "info": {
    "title": "Foo Api"
  },
  "paths": {
    "/WeatherForecast": {
      "get": {
        "tags": [
          "WeatherForecast"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  },
                  "nullable": true
                }
              },
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  },
                  "nullable": true
                }
              },
              "text/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  },
                  "nullable": true
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "WeatherForecast": {
        "type": "object",
        "properties": {
          "date": {
            "type": "string",
            "format": "date-time"
          },
          "temperatureC": {
            "type": "integer",
            "format": "int32"
          },
          "temperatureF": {
            "type": "integer",
            "format": "int32",
            "readOnly": true
          },
          "summary": {
            "type": "string",
            "nullable": true
          }
        },
        "nullable": true
      }
    }
  }
}

It gets loaded along these lines:

<redoc spec-url='swagger/v1/swagger.json'></redoc>

(That's how I tested with the standalone version, it is also how my .NET Core project would load it.)

I used the above with the 2.0.0-rc14 version (that is currently provided in the .NET Core wrapper package) as well as with the rc20 version (by using the redoc standalone html file from the README) and both reproduce the following issu.

The sample URLs generated by Redoc on the right hand side panel will incorrectly(?) include swagger/v1/ in the URLs and generate e.g.:

GET /WeatherForecast
https://localhost:44371/swagger/v1/WeatherForecast

I reported an issue in ASP.NET Core's package that wraps Redoc, but its author remarked that the issue is probably upstream, in Redoc. They mention:

If you look at the raw swagger.json returned by Swashbuckle, you'll see that the server property is actually omitted and therefore should be defaulted to / (also as per the spec). So, to construct the sample request URL, the redoc UI should simply append /products to /. However, it appears to be appending it to the path of the current page instead.

I believe the swagger-ui honors the spec. correctly whereas redoc does not.