[BUG] [typescript-fetch] Unique item arrays (i.e. sets) containing primitive types aren't initialized properly

[davidomid]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Take the following snippet from an OpenAPI spec:

"ExampleModel": {
    "required": [
        "uniqueStringsSet"
    ],
    "type": "object",
    "properties": {
        "uniqueStringsSet": {
            "uniqueItems": true,
            "type": "array",
            "items": {
                "type": "string"
            }
        }
    },
    "additionalProperties": false
}

When typescript-fetch generates the TypeScript for ExampleModel, multiple things happen at the same time:

• The uniqueStringSet property is correctly declared as type Set<string>.
• The ExampleModelFromJSONTyped function is incorrectly generated. In this function, the uniqueStringSet property is just assigned the value of json['uniqueStringsSet'] (which is an array), instead of first setting it to new Set(json['uniqueStringsSet']).

The end result is the following:

• The client thinks the property is of type Set<string> (correct).
• The actual type is Array (incorrect).
• If you try to access a property such as size on the value, the result will be undefined (as that doesn't exist on an array), which is a runtime bug.
• If you try to access an array property such as length, the TypeScript compiler will complain, as it expects you to use size instead (length doesn't exist on Set), which is a compile-time bug.

There doesn't appear to be a workaround for this, except for manually setting the value of uniqueStringSet after the ExampleModel object has been created. This suggested workaround doesn't work for typescript-fetch.

openapi-generator version

7.8.0, although the bug appears to be in previous versions too.

OpenAPI declaration file content or url

N/A, please see example above.

Generation Details

You can reproduce this with the default client generation settings. For example, I run this command to generate my client:

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate \
    -i [MY OpenAPI SPEC URI HERE] \
    -g typescript-fetch \
    -o /local/generated

Steps to reproduce

Generate a typescript-fetch client from an OpenAPI spec containing the above structure.

For my own API spec, I declared the following class in my C# .NET API:

public class ExampleModel
{
    [Required]
    public ISet<string> UniqueStringsSet { get; set; }
}

Related issues/PRs

This looks like a similar issue for typescript-rxjs, but it was opened 2 and a half years ago and not resolved. The provided workaround doesn't seem to work for typescript-fetch (explained here):

• [BUG] typescript-rxjs generate types for fields with uniqueItems property as Sets #11508

Not 100% sure if these other issues are related, but they might be:

• [BUG][typescript-fetch] Set of Primitives not serialized as Array #10770
• [Feature] [TYPESCRIPT] Generator parses to Array instead of Set #8258
• [BUG][typescript-fetch] A request body of type Set fails at runtime #18986
• [BUG] [typescript-axios] Set and Array type parameters are not generated #12649

Suggest a fix

Draft PR here (WIP): #19521

Essentially the bug seems to be caused by isPrimitiveType being true for an array when it contains primitive types. This therefore means the templating is bypassed for the new Set() logic.