Support Int128 and UInt128 in API binding, ApiExplorer, etc.

[DamianEdwards]

.NET 7 introduces the new Int128 and UInt128 structs to represent 128-bit numbers. Attempting to use these new structs in parameters of or responses from minimal APIs or MVC APIs results in broken behavior though, as the type inference logic and serialization doesn't recognize these types.

For example, the following minimal API ends up being described as accepting a string parameter and returning a complex type Int128 with no members (see auto-generated swagger document further below):

app.MapGet("/numbers/{number}", (Int128 number) => new NumbersResult(number, (long)number))
    .WithName("Numbers");

record NumbersResult (Int128 Number, long AsLong);

{
    "openapi": "3.0.1",
    "info": {
        "title": "WebApplication6",
        "version": "1.0"
    },
    "paths": {
        "/numbers/{number}": {
            "get": {
                "tags": [
                    "WebApplication6"
                ],
                "operationId": "Numbers",
                "parameters": [
                    {
                        "name": "number",
                        "in": "path",
                        "required": true,
                        "schema": {
                            "type": "string"
                        }
                    }
                ],
                "responses": {
                    "200": {
                        "description": "Success",
                        "content": {
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/NumbersResult"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "Int128": {
                "type": "object",
                "additionalProperties": false
            },
            "NumbersResult": {
                "type": "object",
                "properties": {
                    "number": {
                        "$ref": "#/components/schemas/Int128"
                    },
                    "asLong": {
                        "type": "integer",
                        "format": "int64"
                    }
                },
                "additionalProperties": false
            }
        }
    }
}

[danmoseley]

Just curious do we know of real scenarios for this or is it just completeness (like supporting Half, etc)

[captainsafia]

Triage: @DamianEdwards will validate if this is still an issue given that it seems like the appropriate TryParse overloads do exist in the BCL.

[DamianEdwards]

So parameters are parsed correctly, but the schema of Int128 is inferred incorrectly (both as parameters and response type). A query parameter of type Int128 is described as a string, and an Int128 member on a schema definition is described as a complex type ("object") with no additional properties. This likely means the change needs to be made in SwashBuckle rather than ASP.NET Core.

[captainsafia]

Filed domaindrivendev/Swashbuckle.AspNetCore#2611 to follow-up on the schema-related changes in Swashbuckle.