`additionalProperties` schema is not parsed correctly

[fpoppinga]

Describe the bug
When parsing an OpenAPI spec which contains a schema for the additionalProperties field, the schema does not end up in the parsed OpenApiDocument.

To Reproduce
Steps to reproduce the current behavior:

consider the following minimal spec (example.yml):

openapi: 3.0.0
info:
  title: Sample API
  version: 0.1.9
paths:
  /users:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                  schema:
                    type: object
                    properties:
                      data:
                        type: string

And the code:

using Microsoft.OpenApi.Models;
using Microsoft.OpenApi.Readers;

var document = new OpenApiStreamReader().Read(File.OpenRead("example.yml"), out var diagnostics);

var additionalProperties = document.Paths["/users"].Operations[OperationType.Get].Responses[
    "200"
].Content["application/json"]
    .Schema
    .AdditionalProperties;

Console.WriteLine(value: additionalProperties.Properties.Count); // prints "0"

This makes it impossible, to generate code based on the type of the additional properties (cf. #microsoft/kiota/62 )

Expected behavior

I would expect the additionalProperties schema to be parsed and contain the schema of type "object" with the properties dictionary containing a field data of type string.

Additional context

I think the parsing is in principle implemented in OpenApiSchemaDeserializer.cs#L161. However, somewhere there must be a bug.

[baywet]

Thanks for reporting this!
Is this something you'd be willing to look into further and submit a pull request for?

[fpoppinga]

I will see if I can have a look this weekend ;-)

[MaggieKimani1]

@fpoppinga the yaml file provided seems incorrect. The additionalProperties field is already defined as an OpenApiSchema object so it shouldn't have a schema field nested within it. Instead the schema should be defined directly within the additionalProperties field. Try using this instead and you'll see the object being populated:

openapi: 3.0.0
info:
  title: Sample API
  version: 0.1.9
paths:
  /users:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                    type: object
                    properties:
                      data:
                        type: string

[MaggieKimani1]

Closing this issue as its been addressed. Feel free to reopen if the response isn't satisfactory.