Empty Dictionary fails to encode

[grahamburgsma]

Description

Returning an empty dictionary as the response body fails to encode.

Error thrown:
EncodingError: invalidValue jsonPayload(additionalProperties: [:]) - at : Top-level jsonPayload did not encode any values.

Reproduction

openapi: '3.1.0'

paths:
  /test:
    get:
      operationId: testEmpty
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                  type: array
                  items:
                    type: string

func testEmpty(_ input: Operations.testEmpty.Input) async throws -> Operations.testEmpty.Output {
    return .ok(.init(body: .json(.init(additionalProperties: [:]))))
}

Package version(s)

OpenAPIKit 3.1.2
swift-openapi-generator 1.2.0
swift-openapi-runtime 1.3.2
swift-openapi-vapor 1.0.0
swift-openapi-context 1.0.0

Expected behavior

The response should be encoded as:

{}

Environment

swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx14.0

[czechboy0]

Seems to be coming from the underlying Foundation.JSONEncoder, so might need to be filed on Foundation unless we identify that the generated code is doing something wrong.

[grahamburgsma]

@czechboy0 I don't believe so, the following works fine:

let empty = [String: [String]]()
let data = try! JSONEncoder().encode(empty)
print(String(decoding: data, as: UTF8.self)) // prints {}

Could be related to something going on here?

[grahamburgsma]

Actually I wonder if I've done something wrong in my spec definition as instead of transforming into a dictionary ([String: [String]]) it generates a struct with an additionalProperties property on it which can't be right.

What is the correct way to have a Swift Dictionary type generated?

[czechboy0]

A freeform JSON-based object? That'd be just:

type: object

If you'd like a dictionary of a specific type, for example integers, then:

type: object
additionalProperties:
  type: integer

[grahamburgsma]

@czechboy0 That doesn't generate a dictionary property though, it gets put inside a wrapper struct which would make working with those types very clumsy. I must be doing something wrong, but this is what I'm seeing.

For example this:

Test:
  type: object
  properties:
    dict:
      type: object
      additionalProperties:
        type: integer

Gets generated into this (simplified):

struct Test {
    struct dictPayload {
        var additionalProperties: [String: Swift.Int]
    }

    var dict: Components.Schemas.Test.dictPayload?
}

Rather than what I would expect (and what all other OpenAPI generators seem to do):

struct Test {
    var dict: [String: Swift.Int]?
}

[czechboy0]

This is expected behavior. If you defined a property in addition to the additionalProperties in the schema for dict, we need a type to define it on. This is to ensure that adding a property doesn't fundamentally change the generated type (from a dictionary to a struct), so it's always a nested type here.

[czechboy0]

@grahamburgsma Does this address your issue or do you believe that there is something we need to change in the generator?

[grahamburgsma]

@czechboy0 I understand why it generates the code as it does now, thanks for explaining that.

The original issue as described still exists though. An empty dictionary response fails to encode.

[czechboy0]

Gotcha, here's a fix, @grahamburgsma: apple/swift-openapi-runtime#103