Incorrect OpenAPI document generation with recursive object that contains a list

[marcominerva]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

In a .NET 9.0.1 Minimal API project with Microsoft.AspNetCore.OpenApi, I have the following endpoint, returning a recursive object that also contains a list:

app.MapGet("/api/categories", () =>
{
    return TypedResults.Ok(new Category { Name = "My Category" });
});

public class Category
{
    public required string Name { get; set; }

    public Category? Parent { get; set; }

    public IEnumerable<Tag> Tags { get; set; } = [];
}

public class Tag
{
    public required string Name { get; set; }
}

With this code, the OpenAPI definition is wrong:

"components": {
    "schemas": {
      "Category": {
        "required": [
          "name"
        ],
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          },
          "parent": {
            "$ref": "#/components/schemas/Category"
          },
          "tags": {
            "$ref": "#/components/schemas/#/properties/parent/properties/tags"
          }
        }
      }
    }
}

If I remove the Parent property from Category, the document is correctly generated:

"components": {
	"schemas": {
	  "Category": {
		"required": [
		  "name"
		],
		"type": "object",
		"properties": {
		  "name": {
			"type": "string"
		  },
		  "tags": {
			"type": "array",
			"items": {
			  "$ref": "#/components/schemas/Tag"
			}
		  }
		}
	  },
	  "Tag": {
		"required": [
		  "name"
		],
		"type": "object",
		"properties": {
		  "name": {
			"type": "string"
		  }
		}
	  }
	}
}

Note that the issue happens even when using a primitive type for the collection (for example string).

Expected Behavior

No response

Steps To Reproduce

Minimal repro at https://github.com/marcominerva/RecursiveObjectIssue.

Exceptions (if any)

No response

.NET Version

9.0.102

Anything else?

No response

[nanny07]

I found out that if you invert the position of the two properties, putting the "Tags" first and then "Parent", it all works as expected

"components": {
    "schemas": {
      "Category": {
        "required": [
          "name"
        ],
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          },
          "tags": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/Tag"
            }
          },
          "parent": {
            "$ref": "#/components/schemas/Category"
          }
        }
      },
      "Tag": {
        "required": [
          "name"
        ],
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          }
        }
      }
    }
  },
  "tags": [
    {
      "name": "RecursiveObjectIssue"
    }
  ]

[mikekistler]

This looks like it might be a dup of #59976

[marcominerva]

The issue still happens with .NET 9.0.2

[captainsafia]

Thanks for filing this issue, @marcominerva!

You've already dupped it to #60381 where I've left a comment but figured I'd make a reference to that comment here.

#60381 (comment)

Similar to the above, I've included a test for this in the branch associated with the backport. For now, closing this one as a dupe of the referenced issue.