Incorrect OpenAPI generation

[johnkors]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

The OpenAPI generator does not generate item-types when multiple arrays have the same type:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddOpenApi();
var app = builder.Build();

app.MapOpenApi();

app.MapGet("/", () => TypedResults.Ok(new SomeType(
  SubtypesOne: [new SomeSubType(1, "First"), new SomeSubType(2, "Second")],
  SubTypesTwo: [new SomeSubType(3, "Third")])
));

app.Run();

public record SomeType(SomeSubType[] SubtypesOne, SomeSubType[] SubTypesTwo);

public record SomeSubType(int Id, string Name);

Even though SubtypesOne and SubtypesTwo are of the same type SomeSubtype[], only the first member gets a valid type generated in the spec json:

            "SomeType": {
                "required": [
                    "subtypesOne",
                    "subTypesTwo"
                ],
                "type": "object",
                "properties": {
                    "subtypesOne": {
                        "type": "array",
                        "items": {
                            "$ref": "#/components/schemas/SomeSubType"
                        }
                    },
                    "subTypesTwo": {
                        "type": "array",
                        "items": {}
                    }
                }
            }

Expected Behavior

I would have expected both subTypesOne and subTypesTwo to emit identical $ref entries for both arrays.

                    "subTypesTwo": {
                        "type": "array",
-                        "items": {}
+                        "items": {
+                            "$ref": "#/components/schemas/SomeSubType"
+                        }
                    }

Steps To Reproduce

Repro:
https://github.com/johnkors/aspnetcore-openapi-repro-bug/

Run the project, and open http://localhost:5121/openapi/v1.json

Exceptions (if any)

No response

.NET Version

9.0.303

Anything else?

Running on .NET 9 and referencing Microsoft.AspNetCore.OpenApi/9.0.8.

Runtime: Microsoft.NETCore.App 9.0.7

[MihuBot]

I'm a bot. Here are possible related and/or duplicate issues (I may be wrong):

• OpenApi: Multiple array properties of the same type do not get the correct type reference #63353
• OpenAPI generation *still* doesn't work with the simplest model with multiple collections in .net 9 #62079
• [OpenApi] $ref not generated for identical lists in same class #63096
• OpenAPI with two collections of same type generates weird internal ref #60931
• Open Api fails to generate correct schema type for some properties #61407

[johnkors]

Seems like it won't get fixed in .NET 9 and will be in .NET 10. No backporting.

#62079

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