[BUG] ELM: C# 8 nullable feature creates uncompilable (Maybe OneOf<PContactInfo>)

[mattiasw2]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
  No, it is the complete swagger.json
• Have you validated the input using an OpenAPI validator (example)?
  Yes
• What's the version of OpenAPI Generator used?
  4.2.0
• Have you search for related issues/PRs?
  Yes.
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

As of C# 8, nullable references types have an anotation '?', and unless it is there, the reference cannot be null.

https://docs.microsoft.com/en-us/dotnet/csharp/tutorials/nullable-reference-types

I have a plain DTO like this,

    public class AccResponse
    {
        // ReSharper disable once NotNullMemberIsNotInitialized
        [NotNull] [Required] public BaseResponse Common { get; set; } = new BaseResponse();
        // public string Id { get; set; }
        [Required] public string Name { get; set; } = "";
        public bool AllowGuest { get; set; }
        public PContactInfo? TechContactInfo { get; set; }
        public PContactInfo? AdminContactInfo { get; set; }
        public bool Blocked { get; set; }
        public bool Disabled { get; set; }
        public int MaximumAllowedNamedUsers { get; set; }
        public string? CreateUserEmailMessage { get; set; }
        public string? CreateUserEmailMessageSubject { get; set; }
    }

and the problem is

    public PContactInfo? TechContactInfo { get; set; }

It is actually exactly the same as

    public PContactInfo TechContactInfo { get; set; }

in C# 7 and earlier, i.e. since there is no [Required], that field can be null.

openapi-generator version

4.2.0

OpenAPI declaration file content or url

Command line used for generation

java -jar openapi-generator-cli-4.2.0.jar generate -g elm -i swagger.json -o src/Swagger/

Steps to reproduce

Just generate and look at the code. There is a warning for another problem,

swagger.zip

[main] INFO o.o.codegen.DefaultGenerator - Model ExcelFormattingBase not generated since it's a free-form object

but you can ignore that. I can simplify those objects.

Suggest a fix

Just make it be treated as if neither ? or [Required] is not there.

[auto-labeler]

👍 Thanks for opening this issue!
🏷 I have applied any labels matching special text in your issue.

The team will review the labels and make any necessary changes.

[mattiasw2]

Notice that string? are correctly handled:

type alias AccResponse =
    { common : BaseResponse
    , name : String
    , allowGuest : Maybe (Bool)
    , techContactInfo : (Maybe OneOf<PContactInfo>)
    , adminContactInfo : (Maybe OneOf<PContactInfo>)
    , blocked : Maybe (Bool)
    , disabled : Maybe (Bool)
    , maximumAllowedNamedUsers : Maybe (Int)
    , createUserEmailMessage : (Maybe String)
    , createUserEmailMessageSubject : (Maybe String)
    }

[mattiasw2]

The nullable mark ? is the problem. I removed it, and the swagger.json file lost the following. So, for now, I will just make sure I do not use that annotation in my DTO classes.

$ git diff swagger.json
diff --git a/sss6elm/swagger.json b/sss6elm/swagger.json
index b5e8f70..2dc258b 100644
--- a/sss6elm/swagger.json
+++ b/sss6elm/swagger.json
@@ -2786,33 +2786,13 @@

           "techContactInfo": {

-            "nullable": true,
-
-            "oneOf": [
-
-              {
-
-                "$ref": "#/components/schemas/PContactInfo"
-
-              }
-
-            ]
+            "$ref": "#/components/schemas/PContactInfo"

           },

[eriktim]

Thanks for your report @mattiasw2. oneOf is currently not yet supported, see #4434. However, I checked it and it does not work when the oneOf is inline in that PR. You would have to create a new schema in components for it.

Two questions:

• Why do you actually need a oneOf here. You only have one case;
• Is there a reason you use nullable instead of required here?

For now using nullable and $ref should work.

[mattiasw2]

The OneOf is generated by NSwag. I added this question there.

RicoSuter/NSwag#2435

[mattiasw2]

When I look at the specification of OneOf at https://swagger.io/docs/specification/data-models/oneof-anyof-allof-not/ it seems to me that adding a OneOf with just one option is useless. I think in this case, you can just remove the OneOf and replace the expression by the single $ref inside.

[eriktim]

Yes exactly. That's why I wonder why it is generated like take. Nevertheless it should work though. It should create a custom type with only one variant.

[mattiasw2]

I think Rico from Nswag has says it should look like this, but I am not sure.

Currently, your generated code will be non-compilable, since the name of the type name includes & and ;

OneOf<PContactInfo>

[pekunicki]

Hi All, @mattiasw2 did you maybe find some workaround for that?
This oneOf for one nullable referenced object is slightly confusing.

[mattiasw2]

@pekunicki I choose to not use the C# 8 nullable feature in my API. The reason I created this ticket is that Typescript handled it, and in the long-term I want ELM to support it too, since for a language like ELM, not-nullable is really important and useful.

[pekunicki]

@mattiasw2 thanks, It seems like a more complex discussion, i.e. whether referenced objects can have nullable prop on the same level. See #5180