[BUG] [typescript-fetch] Regression While Exploding Non-Primitive Types in Request Parameters

[timgrohmann]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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)

Example Spec:

[...]
paths:
  /test-api:
    get:
      operationId: testApi
      parameters:
        - name: dateParameter
          in: query
          schema:
            type: string
            format: date
          required: true
[...]

Description

#22246 introduced a new behaviour regarding query parameter expansion. This breaks the current behaviour with non-primitive types, i.e. Date and DateTime.

The above spec generates:

if (requestParameters['dateParameter'] != null) {
    queryParameters['dateParameter'] = requestParameters['dateParameter'];
}

whereas v7.16.0 would have generated:

if (requestParameters['dateParameter'] != null) {
    queryParameters['dateParameter'] = (requestParameters['dateParameter'] as any).toISOString().substring(0,10);
}

Adding explode: false to the request parameter restores the old behaviour, but having to set explode to false for non-array types does not match my understanding of the spec. Furthermore, exploding arrays of Date/DateTime objects would not work either.

openapi-generator version

v7.17.0, it works in v7.16.0. This is a regression.

Steps to reproduce

Run the typescript-fetch generator against the provided spec with default configuration.

Related issues/PRs

• [typescript-fetch] Fix explode query parameters  #22246

Suggest a fix

I would suggest applying the Date/DateTime to String conversion regardless of explode being set or not.
I will (hopefully) provide a PR later today to address this issue.