Missing "items" elements in schema of class extending ArrayList

[didjoman]

Describe the bug

If a controller returns the interface of a class that also extends an "ArrayList", then the generated Schema of the class (being of type array) misses the "items" property. Furthermore, the class of the item doesn't have a generated schema.

How to reproduce

(Using Java 11, SpringBoot 2.7.2, springdoc-openapi-webmvc-core 1.6.10 based on Swagger-core 2.2.2)
git clone https://github.com/didjoman/springdoc-extension-of-arraylist-issue
Run the application (spring boot).
Run curl --location --request GET 'http://localhost:8080/doc' --header 'Content-Type: application/json'

Expected behavior

The Schema of the "Books" should contain the property "item", with a $ref towards "Book". And there should be a Schema for the "Book" class.
We should obtain a schema like:

{
    "openapi": "3.0.1",
    "info": {
        "title": "OpenAPI definition",
        "version": "v0"
    },
    "servers": [
        {
            "url": "http://localh",
            "description": "Generated server url"
        }
    ],
    "paths": {
        "/test": {
            "get": {
                "tags": [
                    "basic-controller"
                ],
                "summary": "get",
                "description": "Provides a list of books.",
                "operationId": "get",
                "responses": {
                    "200": {
                        "description": "OK",
                        "content": {
                            "*/*": {
                                "schema": {
                                    "oneOf": [
                                        {
                                            "$ref": "#/components/schemas/Books"
                                        }
                                    ]
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "Books": {
                "type": "array",
                "description": "Represents a list of Books.",
                "allOf": [
                    {
                        "$ref": "#/components/schemas/Knowledge"
                    },
                    {
                        "type": "object",
                        "properties": {
                            "empty": {
                                "type": "boolean"
                            }
                        }
                    }
                ],
				"items": {
                    "$ref": "#/components/schemas/Book"
                }
            },
            "Knowledge": {
                "type": "object",
                "description": "Represents the knowledge."
            },
			"Book": {
                "type": "object",
                "properties": {
                    "title": {
                        "type": "string"
                    }
                },
                "description": "Represents a Book."
            }
        }
    }
}

Actual behavior

Today, only the "Books" schema is described, without the "items" property. And the schema for the "Book" class is missing.

{
    "openapi": "3.0.1",
    "info": {
        "title": "OpenAPI definition",
        "version": "v0"
    },
    "servers": [
        {
            "url": "http://localh",
            "description": "Generated server url"
        }
    ],
    "paths": {
        "/test": {
            "get": {
                "tags": [
                    "basic-controller"
                ],
                "summary": "get",
                "description": "Provides a list of books.",
                "operationId": "get",
                "responses": {
                    "200": {
                        "description": "OK",
                        "content": {
                            "*/*": {
                                "schema": {
                                    "oneOf": [
                                        {
                                            "$ref": "#/components/schemas/Books"
                                        }
                                    ]
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "Books": {
                "type": "array",
                "description": "Represents a list of Books.",
                "allOf": [
                    {
                        "$ref": "#/components/schemas/Knowledge"
                    },
                    {
                        "type": "object",
                        "properties": {
                            "empty": {
                                "type": "boolean"
                            }
                        }
                    }
                ]
            },
            "Knowledge": {
                "type": "object",
                "description": "Represents the knowledge."
            }
        }
    }
}

Additional context

It looks like if the controller returns a type "Books" instead of "Knowledge", the doc contains the "items" property and the missing "Book" schema.

[bnasslahsen]

@didjoman,

This is an issue in the swagger-core and here is the code to check it:

	ResolvedSchema resolvedSchema  = ModelConverters.getInstance()
				.resolveAsResolvedSchema(
						new AnnotatedType(Knowledge.class).resolveAsRef(true));
		
		// Then check resolvedSchema.referencedSchemas.get("Books")